Thermostat Replacement - Published in the BMWCC Magazine

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Mike Fishwick
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Thermostat Replacement - Published in the BMWCC Magazine

Post by Mike Fishwick »

M52TU THERMOSTAT REPLACEMENT Mike Fishwick

When the M52TU double-VANOS version of the established M52 engine was introduced in September 1998, it featured a cooling system thermostat which was electrically controlled. These thermostats are now widely used, as they enable the engine management system to maintain coolant temperature within very close limits, thereby optimising operating conditions and so reducing exhaust emissions.

The thermostat operates against a return spring, compressed between the thermostat valve and its plastic housing, which also incorporates the cooling system inlet and outlet passages. The lugs retaining the thermostat to the housing are therefore under considerable pressure from the return spring.

Even though the prototype thermostats must have been subjected to a considerable number of test cycles, within a year owners began to experience failures on such a scale that BMW finally realised a widespread problem existed.

Although – surprisingly – no general recall was issued, a Service Instruction dated May 2000 formalised the problem, which could manifest itself by the engine under or overheating. Overheating sometimes illuminated the ‘Check Engine’ warning lamp, with appropriate fault codes (168 or 222) being logged in the management system’s memory.

My Z3 has one of the early M52TU engines, having been built in October 1998, and after 63,000 miles it suddenly began to exhibit a suspiciously long warm-up period. I had already decided to replace the thermostat on a preventative basis before the summer holidays, and had therefore made the necessary preparations.

Although many owners may feel daunted by the prospect of tearing their BMW to pieces, it is not rocket science, and most BMWs are in fact easy to work on, coming apart easily and in large pieces.

A special tool was manufactured to hold the fan pulley while unfastening the nut securing the viscous fan coupling. This took the form of a piece of steel plate, shaped to fit around the coupling nut while secured to the pulley by two opposite bolts, with a long handle welded to it. The coupling nut is quite large, a suitably thin 32 mm (or 1¼” AF) spanner being required.

Another tool makes removal and replacement of the alternator belt much easier, by locking the tensioner pulley in its withdrawn position. This takes the form of a 6 mm pin (a bolt will do) about 60 mm long, but for added convenience I welded it to a 110 mm handle, made of 20 mm square tube.

Apart from the thermostat and its cover joint, the only parts required were a new radiator drain plug with ‘O’ ring, and the cylinder block drain plug sealing washer.

On cars over ten years old it would be good practice to also replace the ‘O’ ring seals inside the quick-release couplings which connect the radiator hoses to the thermostat housing. These are not listed by BMW, but are available from most hydraulic equipment specialists.

This is also a good opportunity to carefully examine all hoses in the cooling system – including the heater – and replace any swollen or damaged items. In particular, check the hose between the expansion tank and the block, as on some older cars this is known to be rather short, and can be affected by engine movement.

The first step is to completely drain the cooling system, by removal of the radiator and cylinder block drain plugs. Needless to say, this is an excellent opportunity to flush the cooling system and change the antifreeze! Remember to drain the heater by selecting its hottest setting and turning the ignition on, in order to open the heater discharge solenoid valve. The drain plugs can then be replaced, using new sealing rings, and tightened to 25 NM (block) and 8 NM (radiator).

While the front wheels are jacked up, the air conditioning drive belt – if fitted – and the alternator drive belt are removed, after compressing their tensioner pulleys using a T50 Torx key. With the tensioner for the alternator belt locked in the fully-compressed position, pass the belt over the fan by feeding it around each blade in turn. Mark both belts for replacement in their original direction of rotation.

These Poly-Vee belts normally have a life of at least 100,000 miles, but whenever removed they should always be carefully checked for cracks or damage.

Working from the top, withdraw the expanding rivets securing the top of the fan shroud, and remove the hose clips at the radiator connections. Withdraw the wire clips locking the radiator hose connectors to the thermostat housing, and the expansion pipe to the header tank. These connectors are a tight fit, and some gentle persuasion may be required to release them. It may be preferred to leave the bottom hose connected to the thermostat housing, and pushed out of the way until the fan has been removed.

The hoses can now be removed, then the cowl moved backwards against the fan, and secured with tape. The radiator securing clips can be released (unlock by inserting a small screwdriver into the clip, and lever forwards) and the radiator lifted clear. Remember to disconnect the air conditioning condenser fan auxiliary switch, if fitted. The cowl can now be removed.

With the radiator removed it can be thoroughly cleaned, and the cables which pass around it checked for abrasion damage etc. Removal also enables the front of the engine to be properly cleaned, and after an hour or so spent rubbing with steel wool it will positively gleam. It will not make it go any better, but it looks nice!

While holding the viscous fan coupling nut (32 mm or 1¼” AF spanner) remove three of the M6 bolts securing the fan pulley, and – using longer bolts – secure the holding tool in position, using two opposite bolt holes. Now unfasten the coupling nut, remembering that it has a left-hand thread.

With the fan out of the way, depress the wire securing clip of the thermostat electrical connector, and unplug it. Remove the bottom radiator hose, if it was not previously uncoupled from the thermostat. Now slack off the front nut on the stud at the engine lifting eye (which Heather uses to secure the washing line when we are camping!) and remove the bolts around the thermostat housing – three M6 and one M8. After tilting the lifting eye as far as it will go, the thermostat housing can be swivelled and removed.

In my case, both thermostat mounting lugs had fractured, allowing it to expand under the influence of the return spring. I was lucky, as it had not completely closed the return from the radiator, so permitting a reduced flow into the engine at all times. Although in summer this would have caused a slow warm-up followed by overheating, during winter conditions it simply extended the warm-up period.

Replacement was, as they say, the reverse of the removal procedure, with no unpleasant surprises. Fit the radiator bottom hose to the thermostat housing before fitting the fan – after inserting the locking clip, firmly push the connector over the thermostat housing until it clicks into position.

The water pump pulley is again held by the special tool in order that the viscous fan coupling nut can be tightened to 40 NM (30 lb-ft) which is about the threshold of pain for one hand at radius of 12 inches.
The radiator can now be carefully replaced, then its securing clips engaged and fully tightened with a small screwdriver by gently levering backwards. Fit the bottom hose and (if fitted) the air conditioning condenser fan switch connector. Remember to place the fan cowl over the fan before replacing the radiator!

With the tensioner pulley locked in its retracted position, the alternator drive belt can be positioned, after which the tensioner can be slowly released. The air conditioning compressor belt does not have a locking device, but is easy to replace.

Although the drive belts can be fitted before replacing the cowl and radiator, fitting them afterwards provides good practice for any future roadside emergency. Do not wait for it to happen – practice in your garage! Needless to say, a spare belt, with the Torx key and locking pin are worth carrying, but preventative replacement is the best option.
When refilling the coolant system switch the ignition on, with the heater set to its hottest position, in order to purge the heater system. For every litre of antifreeze used, fill the container with water (preferably de-ionised) to give the ideal 50% mixture. This will maximise the anti-corrosion content to last for the next four years or so.

Although in M52TU form the engine does not have any bleed screws, there is one on the expansion tank – a large circular plug, marked with a deep cross. Remove this while filling the cooling system, and replace it before starting. With the filler cap removed and engine idling, remove the bleed screw, and replace it when water begins to flow. Briefly run the engine three or four times to about 4,500 rpm, then switch off, check the level, and replace the cap.

Run the engine for a few more minutes, then check the coolant level. Repeat this check a couple of times until normal operating temperature is reached, then stop the engine and allow it to cool down before finally checking the level. Remember to also check the hose clips, drain plugs, and thermostat bolts for tightness, and examine all connections and joint faces for any sign of coolant leakage before road testing.

The engine was now back to its usual half mile warm-up period, instead of about five miles – a great improvement, which was followed by an oil and filter change to remove the inevitable build-up of moisture and unburnt fuel caused by prolonged cool running.

This is an interesting task, which is within the capabilities of most practical owners. It is always satisfying to find the definite cause of a problem, and for those who have the interest such work helps to improve the man-machine relationship beyond that attained by simply driving the car.
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ZZZEMMCO
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Mike.s "How To"

Post by ZZZEMMCO »

:rtm: Great Article and piccies Mike, even a :dunce: like me could follow it.
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Bestgear
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Post by Bestgear »

Good write up... took longer to read than to actually do it!!

I would stress that the plastic bleed screws are really fraglie and break if horsed up too tight. They are only £2 each if you need a new one.

Did any opf the Z3's have a plastic impellor on the water pump? They were known to break up and send lots of debris through the cooling tracts... If you are swapping the thermostat, changing a pump is only £27 and another 10 mins work...

David
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AndyBass
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Post by AndyBass »

Mike, the thermostat on my M52TU 2.8 failed at 17,000 miles! The car is a 1999 build. Both lugs had broken off and the car was not getting up to temperature at all, not even coming out of the blue zone. I was able to change the thermostat without removing the fan and assorted paraphernalia but just taking the radiator off and easing the thermostat through the fan blades without any force.
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Well Done!

Post by Guest »

Well done, Andy - you must have the touch of a midwife!
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AndyBass
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Post by AndyBass »

Actually Im not a midwife, but I'll gladly take a look for you missus, ooohhh errrrr.l
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Glasgow2.8
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I think my '99 has the same problem, really

Post by Glasgow2.8 »

long time to heat up and heater output is quite poor.

I'll look at AndyB's method of radiatior off.... might be easier for me!



Andy, thanks for the credit, Andy

:?:
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Bestgear
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Post by Bestgear »

Guys, removing the fan is a two second job - get a long 32mm spanner or even a £8 halfords fan spanner and hit the end sharpish with a hammer... it will come off easy peasy....

Do remember tho that the thread is left handed, so dont go trying to tighten it!!

D
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S1 AVV
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Post by S1 AVV »

bugger, had my insp 2 carried out 2 months ago. the zed had done 52000 miles. The dealers kindly picked up on the problem. 1 thermostat @ £35 and time @£25. Was shocked at the speed of the warm up, as i had thought it was normal before :shock:
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c_w
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Post by c_w »

I'm going to replace my Thermostat this weekend hopefully, if the dealer has one in stock.

The description lifted from the magazine is unnecessarily lengthy as my brother changed the thermostat on his 99 Z3 2.8 in 20minutes buy undoing the fan and removing then replacing the thermostat and topping up any lost coolant. :? If it wasn't for lack of access to the front of the engine the fan could stay on.

Whilst the thermostat is out I think I'll change the coolant and flush it out too, but I'm not sure why the description of the job above goes in to details of removing belts/radiator and other ancillaries and HAVING to drain the coolant completely??? Do they work for Haynes? :lol: :lol:
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Bestgear
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Post by Bestgear »

...Agreed... a thermostat swap only is quick... and a full flush is no bad thing too...

No way would you need to remove the radiator... just get the fan off and its straightforward.

To be honest, you should not even need a manual if you have any basic mechanical ability.

If you do swap the water pump too, then obviously both AC and drive belots need to be removed (and replaced?? check them while they are off...) The BMW belts are teh easiest belts I have ever had to remove/replace.. the tensioners are excellent.

Only advice to add is dont over tighten the plastci bleed screws as they do break easily...

D
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Radiator Too?

Post by Guest »

Although - as CW correctly states - the thermostat can be removed without removing the radiator, unless you are working for a dealer etc, where time is money and skinned knuckles arre unimportant, I would always remove the radiator first, and also the fan - both items are so easy to remove there is little point in working around them.

The coolant has to be drained (unless you like working on an engine covered in antifreeze) so you may as well spend 5 minutes removing the radiator first. It makes fan and thermostat removal a lot easier, permits the front of the engine to be cleaned up easily, and generally makes the job easier, cleaner, and more pleasurable. What is the point in saving a few minutes at such a cost?

No - I do not work for Haynes (or Clymer - ugh!) who usually suggest a visit to the dealer at the first mention of an special tool. I just prefer to work on my car easily, in good conditions, and enjoying myself in the process! Perhaps my article was over-long for some folk, but it is necessary to remember that not everyone has the obvious dexterity (or shortage of time?) of CW's brother.
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c_w
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Re: Radiator Too?

Post by c_w »

Mike Fishwick wrote:Although - as CW correctly states - the thermostat can be removed without removing the radiator, unless you are working for a dealer etc, where time is money and skinned knuckles arre unimportant, I would always remove the radiator first, and also the fan - both items are so easy to remove there is little point in working around them.

The coolant has to be drained (unless you like working on an engine covered in antifreeze) so you may as well spend 5 minutes removing the radiator first. It makes fan and thermostat removal a lot easier, permits the front of the engine to be cleaned up easily, and generally makes the job easier, cleaner, and more pleasurable. What is the point in saving a few minutes at such a cost?

No - I do not work for Haynes (or Clymer - ugh!) who usually suggest a visit to the dealer at the first mention of an special tool. I just prefer to work on my car easily, in good conditions, and enjoying myself in the process! Perhaps my article was over-long for some folk, but it is necessary to remember that not everyone has the obvious dexterity (or shortage of time?) of CW's brother.
Sorry it wasn't meant to be a dig :oops:, just that he said it seemed an easy enough job to do with out having to remove much.
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c_w
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Post by c_w »

I'd thought I'd add my findings now that I have changed my thermostat yesterday.

They are £35+vat from BMW Dealer who tend to keep them in stock. Too expensive in my opinion as they should be subsidised considering they are a poor design and prone to failing; just 2 silly brittle plastic tabs hold the thermostat to the housing under the spring's pressure. Sure enough when I took my old one out the tabs had broken (so 2 pieces of plastic will be floating around the engine somewhere...).

I drained the coolant as Mike suggests, though I didn't undo the radiator drain plug - just the engine block drain plug as I flushed the radiator out with a hosepipe by directing water in the top hose and flushing it round. Whilst the thermostat was out I flushed out the block and also the expansion tank.

The hardest bit for me was removing the viscous fan (or rather locking the pulley to get it undone), in the end I used a wedge in the pulley and using a 32mm spanner hit it with a hammer to loosen it.

The car now warms up much quicker and sits in the centre all the time, whereas these past few days it would drop on the motorway and over cool. The heater is now much much better (though I thought it was good before!!).
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No Dig from CW!

Post by Guest »

Dear CW -

No dig was seen in your comments - just fair comment! It's always quicker to do any job if you can see a way to avoid doing it fully, whihc in many cases is fine - it just depends on one's dexterity, the car's usage history etc.

After having to disconnect the hoses, I still prefer to whipe the radiator out and so gain a lot of extra space to work in - it only takes 2 minutes max, and also avoids any riskn of damage by flying fan spanners etc!

Best wishes,

Mioke F
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Post by estocks »

I'm going to try this but don't want antifreeze over the drive.
1/ Will I need a jack or axle stands or a large bucket to drain the coolant?
2/ Where are the drain plugs and will I need to replace a seal/plug?
3/ Where can the special tools needed be purchased economically?
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Questions

Post by Guest »

1. Just a bucket or deep tray. Axle stands are not necessary, but some kind of ramp is useful - like a concrete block or bits of wood etc. Use your initiative, buy some 2" X 8" timber and make them.

2. The drain plugs are half way along on the side of the block, and on the base of the radiator at the near side.

3. You cannot buy the special tools, but they are easy enough to make. Many people say that the fan nut can be 'shocked' loose with a sharp blow on the end of the spanner - but replace the belt afterwards! The tensioner can be held back with a T50 Torx key, and locked with a long M5 bolt.
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Post by estocks »

It seems there is a new design, where the plastic clips are replaced with metal. PN is 11537511083.

Does the car have to be levelor angled when draining or filling the antifreeze? :dunce:
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Post by estocks »

It seems there is a new design, where the plastic clips are replaced with metal. PN is 11537511083.
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:?: Does the car have to be level or angled when draining or filling the antifreeze? :dunce:

How much fluid does the radiator hold, so I can know how much it should hold without air bubbles?
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Old Model

Post by Guest »

The thermostat shown above is for a pre-Sept 98 engine, which does not have the advantage(?) of electric control.

The post-Sept 98 M52TU engine uses the electrically-controlled thermostat, whic is supplied with an integral black plastic housing.

I imagine that those who can change a thermostat without removal of the fan have the earlier type of thermostat, which is retained by its cover, secured by two bolts.
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Post by wildbillybeemer2 »

Saturday, sunshine came out.

- Drained Radiator
- Figured out how to remove riverty things
- Pulled out rad
- Spotted the 3 allen key holes on the fan, removed and pulled off
- Remove thermostat nice and easy
- Plug new one in
- Put it all back in
- Fill up Rad
- Tighten radiator cap with socket set as screw head was threaded
- Say "sheeeet" as the cap snaps off to prevent over-tightening (this really should be hand tight me now thinks..

Apart from that, job done, problem gone, all GOOD!!

I didn't use or make any special tool, I just had a friend to help and I admit a tiny amount of coolant did touch on one of the belts but I had a hose ready to wash it all away.

Got to say looking at Mike's pics, did you do this on a brand new engine??? :) lovely and clean.

Also have to agree, trying to change thermostat through the fan or with the radiator on is near on pointless, I got the new coolant from BMW themselves for £22 for 3 bottles and now have enough spare to refill the rad anyway.

Thanks for the tips and remember not to overtigthen that radiator cap like I did, not sure it will be possible to unscrew again... anyone know?
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Cap

Post by Guest »

I'm puzzled - how did you tighten the radiator cap with a socket set?

Oh - my engine had done about 45000 miles when I changed the thermostat, but I'm a compulsive metal polisher!
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Re: Cap

Post by wildbillybeemer2 »

Mike Fishwick wrote:I'm puzzled - how did you tighten the radiator cap with a socket set?

Oh - my engine had done about 45000 miles when I changed the thermostat, but I'm a compulsive metal polisher!
The cap on the bottom? well basically the blue plastic part was so worn I couldn't use a screw driver to undo it so I used a socket set.

Naturally later on I was so pleased that I'd finished the job with no disasters that without thinking it through I used the same method to put it back on, what I should have done was hand tighetn it all the way and then give it a gentle little 1/4 turn with the socket but kinda went for a full turn and 'snap' off it came.....

Looking at it now I'm guessing it's designed with the plastic on the end to prevent over-tightening...
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Post by wildbillybeemer2 »

*maybe I should have put bottom radiator plug bit*
*not the actual radiator cap lol*
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Plastic

Post by Guest »

The correct description is 'Drain Plug.'

I would reckon on tightening it by hand, then a quarter turn.
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aceman
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Post by aceman »

Well finally got round to replacing the thermostat on mine today after I had noticed it not getting upto temp now we are getting more cold mornings. It was a classic failure just like in Mike's pictures with the plastic posts broken. Also replaced the water pump for a metal impeller one and the drive belts as the originals were badly perished. I needn't of done the water pump but thought in for a penny in for a pound and replaced it as a preventative measure, I must say though that the one I removed appeared to be in very good condition with no play in the bearings and no cracks in the plastic impeller. The only problem I had was removing the fan at the start as I didn't have a "fan tool" so thought I would try to shock it off with belts taking the strain as suggested by some people but it wasn't to be so I had to manufacture my own tool which did the trick but added a couple of hours to the job as I had to go and source some 1/4" flat steel.

All in all a very productive day and I am more at one with my Z than I was yesterday. Many thanks to Mike for this guide as it helped me tremendously so well done that man ! :D
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Post by And_101 »

Just replaced my thermostat today.

No need to faff about with special tools to remove the fan - on mine there were 3 allen screws holding the plastic fan to the viscous hub - simply remove those, the fan blades come off and easy access to the thermostat.
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Post by Ian_C »

And_101 wrote:Just replaced my thermostat today.

No need to faff about with special tools to remove the fan - on mine there were 3 allen screws holding the plastic fan to the viscous hub - simply remove those, the fan blades come off and easy access to the thermostat.
You must have small hands then! I couldn't get my hands & allen key into the space between the fan and the radiator when I changed my fan. For those of you with magnificent manual dexterity here's a ref pic of where the allen screws go on the fan (apologies for the inclusion of the horror pic of the old fan :shock: ):

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Post by And_101 »

myredzed wrote:
And_101 wrote:Just replaced my thermostat today.

No need to faff about with special tools to remove the fan - on mine there were 3 allen screws holding the plastic fan to the viscous hub - simply remove those, the fan blades come off and easy access to the thermostat.
You must have small hands then! I couldn't get my hands & allen key into the space between the fan and the radiator when I changed my fan. For those of you with magnificent manual dexterity here's a ref pic of where the allen screws go on the fan (apologies for the inclusion of the horror pic of the old fan :shock: ):
I should have added that I removed the radiator first - that was easy, and it did mean not having to risk undoing the drain plug, since it was then a doddle to flush the radiator out..
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