It's getting hot in here

[maser_4200]

Hi there,

I am having a heat issue - too much it seems...

Temperature gauge is rising from the usual rock steady 90 deg C to 100 deg C when the car is fully warmed. It drops back to 90-95 deg when moving, then rises again when stopped at lights / slow moving traffic.

This only started a couple of weeks after getting the coolant replaced as part of a full service. We initially thought that it was the (valved) coolant tank cap was not maintaining sufficient pressure in the system (some spill over seen on the tank). So the new cap is on (now with a hose, so they part seems to have changed). The system had lost about 100ml, so that was topped up, and the system pressure tested - it doesn't appear to have any leaks.

But the darn temperature is still going up to 100 deg C. I'm driving it as little as possible / short distances.

The thermostat was replaced about 2 years ago. I would have thought if this was stuck closed, the system would blast in to the red as the coolant boils off in the engine? And it if was partially open, the car would not warm up properly?

Any ideas on what is going on? Thanks!

 

[CatmanV2]

Sounds like the 'stat is failing to open fully. But, are both your fans coming on?

C

 

[maser_4200]

Sounds like the 'stat is failing to open fully. But, are both your fans coming on?

C

Thanks - fan seems to be be running. Good point though - I must double check if both fans are running - had only had a cursory look, and didn't realise there were two ahem (just had a look at the full diagram on Eurospares).

From what I gather, if the resistor pack fails, the usual failure mode is the fan cutting in at full speed rather than only operating at low speed (i.e., if it burns out, full voltage is applied to both fans). Is this correct?

I could replace the thermostat I guess. Is there any way to diagnose other than replacing?

Is that more likely than a blocked or damaged radiator? We were considering flushing the system out next.

 

[CatmanV2]

Yes, if the resistor goes, then there will be no low speed fan action, it'll just go to full tilt. But if one of the fans fails, you might get the sort of issues you're describing.

I'd have thought that radiator issues would result in proper over heating even when driving, but it's work a thought.

You might be able to diagnose the stat by feeling the temp on the output hose when it should have opened, but that might not tell you enough if it's opening part way. Infra red thermometer should read the same temperature either side of the stat (or near as **** it) If it doesn't I think there'd be a problem.

Not easy, unfortunately.

C

 

[ANY]

Air in the system after the coolant change?

 

[CatmanV2]

Air in the system after the coolant change?

Not a bad shout, actually!

C

 

[AndyG]

Only sure way to fill the system is vac all the air out and then pressure fill the system, you can try leaving the cap off over night and see if the air lock works it's way out.

 

[maser_4200]

Yes, if the resistor goes, then there will be no low speed fan action, it'll just go to full tilt. But if one of the fans fails, you might get the sort of issues you're describing.

I'd have thought that radiator issues would result in proper over heating even when driving, but it's work a thought.

You might be able to diagnose the stat by feeling the temp on the output hose when it should have opened, but that might not tell you enough if it's opening part way. Infra red thermometer should read the same temperature either side of the stat (or near as **** it) If it doesn't I think there'd be a problem.

Not easy, unfortunately.

C

Air in the system after the coolant change?

Only sure way to fill the system is vac all the air out and then pressure fill the system, you can try leaving the cap off over night and see if the air lock works it's way out.

Thanks all - I have a net list of this to check.

• Radiator cap regulates pressure in system. Replaced cap
• Both fans running? Very hard to see – think so
• Fan speed resistor burned out? Would mean only high speed operating?
• Air lock? Need to check “Only sure way to fill the system is vac all the air out and then pressure fill the system, you can try leaving the cap off over night and see if the air lock works it's way out.â€
• Blockage in system? Need to flush.
• Blocked radiator? Check for hot/cold spots in radiator.
• Thermostat not opening fully? Take off thermostat housing and test in progressively hotter water to check operation
• Leak in system? Pressure test. Seems to have tested OK
• Temperature sensor incorrect? Can check temperature with infrared thermometer

 

[CatmanV2]

Thanks all - I have a net list of this to check.

• Radiator cap regulates pressure in system. Replaced cap
• Both fans running? Very hard to see – think so
• Fan speed resistor burned out? Would mean only high speed operating?
• Air lock? Need to check “Only sure way to fill the system is vac all the air out and then pressure fill the system, you can try leaving the cap off over night and see if the air lock works it's way out.”
• Blockage in system? Need to flush.
• Blocked radiator? Check for hot/cold spots in radiator.
• Thermostat not opening fully? Take off thermostat housing and test in progressively hotter water to check operation
• Leak in system? Pressure test. Seems to have tested OK
• Temperature sensor incorrect? Can check temperature with infrared thermometer

Checking to see if the fans are running really shouldn't be difficult. Place your hand behind each in turn. You'll *feel* if they are running. Obviously exercise care around spinny crushy spikey things like aux drive belts, but you should be fine.

Not 100% convinced about the need to vac to prevent air locks, but that may be my ignorance about this particular engine

C

 

[Chrisbassett]

I think the two fans come on at different times/temperatures. I remember a second vibration starting in summer traffic

 

[alfatwo]

Partial head gasket failure if there constant air in the cooling system..

Dave

 

[Gp79]

Crack open the two bleed screws on the front of the engine, one on each bank, as it does sound like an air lock if it was fine before replacing the coolant.

Also with the cap off the expansion tank give the top / bottom hoses a good squeeze to try to dispel any air

 

[ANY]

Crack open the two bleed screws on the front of the engine, one on each bank, as it does sound like an air lock if it was fine before replacing the coolant.

Also with the cap off the expansion tank give the top / bottom hoses a good squeeze to try to dispel any air

Exactly!

 

[CatmanV2]

I think the two fans come on at different times/temperatures. I remember a second vibration starting in summer traffic

Indeed. But if the temp is getting near 100 at an idle I'd expect them both to come on.

C

 

[maser_4200]

OK this is weird.

We think it may be the gauge.

The ECU (according to the diagnostics) is apparebntly reading 90 deg even when the gaugue is reading 100/110 deg.

The system pressure tested OK.

It has been hard to check the actual temperature of the system.

So a question - is it correct that a single sensor feeds a signal to both ECU and gauge? Why is the gauge dropping from 100/110 deg to 90 deg when moving if the temperature is actually OK?

 

[CatmanV2]

What are you reading the diagnostics with?

C

 

[maser_4200]

Hmm I think it's AG Autronica Leonardo

 

[maser_4200]

OK a quick update.

It has been reported that from stone cold, the ECU is reading 15 deg C. The gauge is reading 60 deg C.

Therefore, either the gauge or the temperature sender is bad. We are going to replace the temperature sender and see if there is any change...

A photo of the gauge when warmed up / reading over 90deg is attached.


(Note car is stopped - speedo stop is above 0mph as on all of these cars]

 

[CatmanV2]

If you look, you can see the pin that stops the speedo from dropping to zero...

C

 

[maser_4200]

If you look, you can see the pin that stops the speedo from dropping to zero...

C

Yep! I remember well when I sent the car back to the dealer with a "broken" speedo and it took a while before they copped that it is the same on all cars! The stop is lower on the temperature gauge, so it doesn't have the same excuse...

I'm hopeful that a new temp sender will tell a lot about the system