Overheating, stuck thermostat symptoms?

[B19GRR]

Hi all,

Can anyone confirm my suspicions that my stat is stuck closed? When driving slowly the temp rises rapidly and if I get stuck in a jam then it will go in to the red. I can relieve it by turning the heater all the way up with fans on full. Once on the open road it will return and maintain correct running temp. This is happening in the current weather, I was out in -3C today pushing red on the gauge - joy!

Heating problems seem to be dogging all parts of my life at the moment!

Cheers,
Rob

[Magic919]

Not sure I can advise regarding the dogging.

If the stat sticks the rad will not get hot. Take a look and feel under the bonnet.

[mk2 24v]

if the stat is stuck closed then its possible. but id be inclined to check the water is being circulated, sounds like water pump troubles to me

what engine/car is it in?

[IainZ]

Start with checking the coolant level (when the engine is cold). If its low then clearly you need to find out why.

If the pump is driven off a V-bolt, check the tension on that, otherwise would suspect its more likely an issue with the pump itself.

T-stats don't often stick closed, more usual is tha the spring goes weak & they won;t close (resulting in cold running temps)

Edited by IainZ on Saturday 4th December 10:44

[GavinPearson]

If the thermostat bypass has hyperextended this could well be an issue. Fit a new part immediately, flush out the old coolant, use brand new coolant.

[B19GRR]

Hi all,

Yup, checked coolant and it was very low, added a few litres of water in there to bring it up and bled the system, I'll check again tomorrow to see if anymore has leaked out. It's booked in for Tuesday, even if the RAC has to get me to the garage.

It's my E39 528i, normally good as gold but they are noted for a slightly fragile cooling system. Hopefully something straightforward rather than new rad etc. I'll find out soon enough.

Cheers,
Rob

[B19GRR]

Oh, forgot to mention, car had a new waterpump back in October so that should be fine, but worth getting the guys to check over.

Cheers,
Rob

[davepoth]

B19GRR said:

Hi all,

Yup, checked coolant and it was very low, added a few litres of water in there to bring it up and bled the system,

No antifreeze? in this weather?

If the coolant was very low it's gone somewhere. I'd suggest getting a compression test done pronto.

[IainZ]

B19GRR said:

Hi all,

Yup, checked coolant and it was very low, added a few litres of water in there to bring it up and bled the system, I'll check again tomorrow to see if anymore has leaked out. It's booked in for Tuesday, even if the RAC has to get me to the garage.

It's my E39 528i, normally good as gold but they are noted for a slightly fragile cooling system. Hopefully something straightforward rather than new rad etc. I'll find out soon enough.

Cheers,
Rob

Coolant doesn't just disappear for no reason. Suggest check under the oil filler cap for mayonnaise for a start. If its there then the head gasket has probably gone. The symptoms you have been seeing are where the top end of the engine has got very, very hot at idle because there isn't enough coolant being pumped around. Then when you increase the engine revs there is still enough in the system to cool the thing down.

That can do the cylinder head no good at all so make sure you keep the system topped up and add antifreeze as well till you find the problem & fix it. In this weather if you just add water you risk the system freezing & then you really will have a problem.

You have a leak somewhere, if its not the head gasket then check for split hoses or loose hoseclamps - look for coolant stains on the radiator or around the water pump. Check the expansion tank is not cracked.

If you can get your hands on one a cooling systm pressure test kit might show you what you need to know. If not then try warming the thing up & increasing the revs a bit (to increase the pressure in the system) & see what you can see. If you can smell coolant inside the car the heater matrix may have gone

[B19GRR]

Job done, one of the pipes to the heater core was leaking. All good now, no HGF horrors to reprt thankfully.

Did forget to mention I had the water pump replaced back in October. Had them replace the stat anyway as a precaution, might as well when the system's drained.

Cheers,
Rob