Overheating

[carritts]

I have an annoying overheating problem. Often, the car warms up from cold very quickly and goes straight into the red zone after approximately 5 minutes. It then stays there for the next 10/15 minutes before dropping down to normal temperature and not budging,. It doesn't do this again in the same day; despite being sat for several hours. I've done the obvious and changed the thermostat (twice). I was advised that it could be the water pump. Apparently, some have a plastic impeller that can slip on its shaft. This sounds feasible. Has anyone else had this issue? It's a big job to change, so I don't want to do it unless someone has had the same experience? Thanks.

[Magnet]

Hello Sean, 

Sorry to hear of your issue. Cutting to the chase, I’ve never know a water pump to be the cause of overheating ( without prior protest via. noise) even during the time I had hair - and that was a long time ago! 

Thermostats? Make Sean? 

Actual monitored running temperature checked? 

Kind regards,

Gareth.

[carritts]

Thanks for the response. I can't recall the makes, but to have exactly the same issue with both thermostats indicates it's not a thermostat issue. Also, given that the temperature reading is stable after the initial overheat and that the issue is intermittent,  I'm very doubtful that it is a sender or gauge issue. The only plausible cause is as I've stated and this was suggested by a local mechanic.  I was really looking for someone with a similar experience and a solution?

Thanks again. 

[Magnet]

Hello Sean,

It seems either no one on here has experienced similar issues to yours as a result of a faulty water pump, or might have, but has not bothered to respond.

With the elapse of time, I guess you will now have to follow your mechanic’s diagnosis and renew the pump. 

Sometimes advice is asked for as a confirmation of an already held viewpoint, and alternative advice simply complicates the situation. 

Kind regards,

Gareth. 

[carritts]

Thanks Gareth, I've checked the pump out by disconnecting the return feed and monitoring flow. It looks good as there is flow and flow increases with revs. I am now at a complete loss. Bugger.

 

[Magnet]

Hello Sean,

Good news that you have been able to discount the water pump as the possible culprit - particularly for your wallet! So mechanic’s diagnosis is unlikely to be correct then.

‘Now at a loss....’ My suggestion for going forward may be as good as your mechanic’s ! but.....:- 

I would not discount the thermostat/s, since the symptoms could be explained by such a faulty component. 

OK., two thermostats tried, so two cannot be faulty. Well you would think so, but dependent on the (aftermarket?) source, that bit of logic may be highly questionable. 

In the absence of anyone coming up with any better idea, I would spend my money on a main dealer one, or perhaps Bosch if they do one, but (in caps) test it before fitting. You will need some cotton thread and a thermometer - just let us know if you are unsure about how to test the good-make new one. 

Does the car use any coolant? 

Kind regards, 

Gareth, 

[carritts]

Thanks Gareth, I'll ponder some more as a thermostat change is a pain, but I'll check the removed thermostat. I don't lose any coolant.  Cheers 

[carritts]

Thermostat is good. I've decided to change the sender as it's cheap and looks pretty straightforward to fit. I'll keep you posted.

[Magnet]

‘Thermostat is good..’ How did you test it Sean? 

Kind regards,

Gareth. 

[carritts]

Gareth, I tested it in boiling water. It opened fully and closed again. Not massively scientific,  but good enough. 

[Magnet]

Sort of scientific enough Sean, but not a good a test as it could be. 

Better test in my opinion:- 

Place the thermostat in a saucepan of water and heat until it opens. When it’s open, tuck a single length of cotton about 18 inches long under the seat of the thermostat - where it opens- and ensure it stays there until the thermostat closes - obviously water cooling down. 

Go and have a cup of tea while the thermostat returns quietly to room temperature. Ideally leave it for a few hours if you can. 

You can now dangle the thermostat by its string, so start to heat the water with the stat dangling in it and stir the water with an accurate thermometer and continue heating slowly and holding the stat just off the bottom of the pan. Note the temperature at which the stat falls off the cotton I.e. it starts to open. This is the critical temperature measurement. Fully open in boiling water mat suggest it’s OK but doesn’t give any indication of when (below boiling point) it actually opens. A slow (temperature wise) to open thermostat could account for your symptoms. 

Kind regards,

Gareth.