Overheating or thermister problem?

chrig · Post by **chrig** » Fri 09 Mar, 2007 23:14

Was driving around town today and whilst stuck in a couple of queues I noticed the temperature guage raising pretty quickly, something with which I've never had a problem before. And I mean quick, within 1 minute at the traffic lights it had raised to the 75% mark, but just as quickly settled down to the 50% mark when I got moving again (this is where it usually idles).

But just to clarify, there is definitely a problem here as 5 minutes later, when stuck in some more serious traffic it raised right up to the red within a couple of minutes. Pulled over and switched off - there was no major evidence of overheating, the bonnet wasn't even warm to the touch. Leaving it off for a couple of minutes, on restart it was back to 50%

So do I have a serious problem here? What would cause the engine temp to climb? Conversely, how would I identify if it's a fauly reading?

TIA

muppet · Post by **muppet** » Fri 09 Mar, 2007 23:17

would be very serious if you blew a Gasket, could be a jammed thermostat, but I would get it to spannerman in a hurry .

mich · Post by **mich** » Sat 10 Mar, 2007 03:16

A thermostat usually fails safe, i.e. you will run cold and not heat up, could be a cooling system blockage, have you lost any water from the radiator? But if the engine does not appear hot then , it could be the sender unit and/or gauge, you can remove and check the thermostat your self but it does not sound as if that is the fault.

Ian_C · Post by **Ian_C** » Sat 10 Mar, 2007 07:46

Sounds like the temp reading is accurate to me since the needle goes down when you start moving. You could check a couple of things here:

1. Coolant level - if you've got a leak then there might not be much left. IMHO this would give the symptoms you've got since most of your cooling would be coming from airflow over the radiator during forward motion.

2. Fan not working - possible; does it cut in as the temp rises?

I'm almost convinced that you're down on coolant and that you have a leak. I'd suggest topping it up and hunting for leaks.

Good luck

muppet · Post by **muppet** » Sat 10 Mar, 2007 09:12

myredzed wrote:

2. Fan not working - possible; does it cut in as the temp rises?

:

Come to think on it the symtoms do sound like my old CBR 600 , the fan on that did not work had I had to constantly filter through traffic to stop it overheating

benelvin · Post by **benelvin** » Sat 10 Mar, 2007 09:24

In my old metro I could solve that problem by putting the heater and internal fan on full blast

chrig · Post by **chrig** » Sat 10 Mar, 2007 10:27

Tried that Benelvin

Didn't work though!

Yup, it's due a coolant change so I'll try that first - thanks for the advice.

Guest · Post by **Guest** » Sat 10 Mar, 2007 15:15

You could take the engine's temperature, by carefully unscrewing the header tank cap and sticking a thermometer in the water. This would bypass the temperature sensor completely.

Changing the coolant will not make any difference, unless it is (very unusual) full of sludge - you should be thinking about:

(a) Is the viscous fan coupling working - the fan sounds like like a fire siren when it cuts in. Also - is the drive belt loose/greasy/worn?

(b) Is the thermostat working correctly? On cars built from Sept 98 to April 2000 failures are commonplace, and can result in high temperature. This often logs fault codes in the ECU memory.

(c) Is the water pump impeller slipping? While not common, the plastic impeller can come loose on the steel shaft, the effect being more marked at idle speed rather than at higher speeds.

Assuming that the coolant level is OK, and the radiator not full of dead leaves, I would suspect the thermostat.

mich · Post by **mich** » Sun 11 Mar, 2007 01:27

As always, a font of wisdom Mike, I always learn something from your posts, does this thermostat fail closed?

Dave C · Post by **Dave C** » Sun 11 Mar, 2007 07:28

It is possible that the thermostat could have failed not opening fully this would cause the rapid heating at idle as the pump would not generate enough pressure to circulate the system. Another possibility is that the fan is not up to scratch, the viscous coupling may be faulty.
It will need looking at before any damage occurs to the cooling system or engine.
Hope you get it sorted without too much trouble.

Guest · Post by **Guest** » Sun 11 Mar, 2007 11:37

According to the BMW Serice Information, the thermostat can fail in the open or closed position. If closed, the temperature gauge will go high, and sometimes fluctuate of the themrostat is moving around.

chrig · Post by **chrig** » Sun 11 Mar, 2007 20:37

Thanks Mike - on investigating yesterday, I found that the coolant level was way too low. I drained the system and put new coolant in and, thankfully, it seems fine now.

saltcoatsbhoy · Post by **saltcoatsbhoy** » Sun 11 Mar, 2007 22:18

Don't want to be a prophet of doom but the same thing happened to me last August. Did the same as you to rectify the fault. When I took the car in to get brake fluid and coolant changed a month or two later spannerman detected anti freeze dripping at the bottom of the radiator. I believe you can test the integrity of the radiator with a pressure test. In my case a new rad was required.

Guest · Post by **Guest** » Mon 12 Mar, 2007 10:32

Don't be too pleased that you have found something! Kepp checking the level, as an overheating engine will expand the coolant and expel it. Keep an eye on the temperature gauge.

chrig · Post by **chrig** » Mon 12 Mar, 2007 16:26

Thanks Mike - I checked my coolant levels today and noticed it had dropped by around 250ml. However, no problems temp wise, it's sitting at a pretty steady 50% even at short periods of stand-still (haven't had a chance to check on a longer interval). Also no sign of leakage that I can tell so hopefully it was just settling (though I had also just had the engine running so some may still have been in the sytem

).

By the way, next on my service list is brake fluid change and a clutch bleed - don't suppose you have any info on them squirreled away?

Have been searching all day but none of it's DIY related! And the TIS CD is a bit rubbish IMO!

muppet · Post by **muppet** » Mon 12 Mar, 2007 16:29

try and find the leak , happened to me years ago and it was the head gasket that had blown .

chrig · Post by **chrig** » Mon 12 Mar, 2007 19:13

Hopefully won't be head gasket Muppet - no other warning signs that point to that (milky oil, heaters gone cold, white smoke etc).

chrig · Post by **chrig** » Tue 13 Mar, 2007 16:40

Hmm, definitely loosing coolant here, it keeps settling a couple of cm's from the bottom of the reservoir though. If it would just stop bloody raining I could investigage

SpunkyM · Post by **SpunkyM** » Wed 14 Mar, 2007 13:25

You need to wait until the engine is upto normal running temperature before checking for the leak really (make sure the fan has come on). It's typical that only then does the cooling system get pressurised enough to squeeze the water out of somewhere.

Dave C · Post by **Dave C** » Wed 14 Mar, 2007 18:47

SpunkyM wrote:You need to wait until the engine is upto normal running temperature before checking for the leak really (make sure the fan has come on). It's typical that only then does the cooling system get pressurised enough to squeeze the water out of somewhere.

Be careful not to remove the cap whilst hot or the coolant could boil, which would severly scald you!!!

If it is settling at a level whilst still in the coolant reservoir, the leak will most probably be at that height, maybe the reservoir itself has a leak or a poor seal on a hose somewhere.

Hope it gets sorted without too much hassle

zroadster.net

Overheating or thermister problem?

Overheating or thermister problem?

Temperature

Thermostat

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