KV6 slightly overheating. No coolant loss, no airlock, new cap fitted...what's next?

[scoubix]

Folks,

Some of you might remember this thread I did a month ago : http://www.the75andztclub.co.uk/foru...d.php?t=180290

But as symptoms are still present, and more tests have been done, I need expertise on what to look for next.

Symptoms : car is slightly overheating (we're talking 4 degrees here, it has never shot in the red and we're still within tolerance limits). Previously, the car used to drive at temps between 89° and 93°/94°
- car is warming to temperature as expected from cold, slight pause in temperature rising around 92°/93° where car would remain for about 5 to 10 minutes. Assuming this is because of the thermostat opening around 88° +/- 2° and cold water mixing in.
- temperature would then rise to 96° and oscillate anywhere in between 92° (when going down slopes, very long ones even bringing the temp down to 90°) and 99°/100° (when going up hill or in 20km/h traffic with fan off).
- car oscillates most of the time, on even roads and normal driving conditions between 95° and 99°, 96° being the most seen.
- speed, and therefore airflow, has no influence as these temperatures are seen at any speed between 50 km/h and highway speeds. Below 50 km/h, temperature is likely to be in the upper values above.
- fan is perfectly operational and kicks in at 100°. HOWEVER, it seems to me take take quite some time to bring the temperature down to 95° where it would stop. Temp actually keeps on rising to 101° and then 102° after fan has started, before going down. FACT : when staying idle, with box in D position and foot on brake pedal, car WOULD NOT go below 96°, therefore the fan would not stop...unless I put the box in P position, which would then allow it to go down to 95° and fan would stop. Assuming this is because of the increased effort of the engine in D as opposed to in P position. However, this is not normal behavior either.

Already checked :
- tank cap has been replaced with brand new 100 Psi cap secured from Rimmer. (as mine is a launch car, thus early one with 100 Psi spec). No change.
- Looked into the V, there are no apparent sign of thermostat leaking
- Coolant level is at adequate, max level, and has been so ever since I bought the car 16 months ago. I've never added coolant to the car, and there is obviously no coolant loss.
- no difference in behavior whether the ATC is off, in econ, or Auto mode. That is, at cruising speed. In slow traffic, with ATC set to Auto, as the fan is permanently on obviously the car has a tendancy to not go above 98°. BUT this is another proof of slight overheating as air flow with fan on should not let me reach those temperatures.
- there are no over pressuring happening from exhaust gases (which is a relief obviously). Not only there are no smell of exhaust gases, but when I open the tank when car has cold down overnight, there is no air hiss.
- drove the car with the cap slightly off just to allow over pressure, if any, to vent out and see if it made any changes to the temperature. No change at all, and no coolant overflow.
- there is no airlock in the system, checked with raising the tank and opening up bleed screw as per proper MGR procedures.
- coolant was last changed in october 2009 when belts, thermostat, water pump, inlet manifold gasked, the whole shebang, was done by MGR specialist with previous owner.

My own thoughts so far :
- if thermostat was slightly sticky and not opening fully as it should, it would only delay the mixing of all water, but once everything has mixed, I still should get ideal temperatures, meaning 92/93. True/false?
- water pump is not as effective as it should any more? Not leaking obviously, but not allowing enough water flow?
- small blockage happening somewhere in the system, possibly the oil cooler?
- radiator is getting faulty (less likely as they usually outlive the car...?)

I'm nowhere near dramatic situations such as the needle going 12 o'clock, but while the outside temperatures are still quite cool, I'm a bit worried it might be worse during the summer

And obviously I want to nail it down

[kaiser]

1. Reduced flow of water.
a.The thermostat does no longer open fully, and the flow through the radiator is lower than it used to be.
b. there is another part blockage of the flow, (oil cooler?)
c. The pump no longer pumps the same volume (unlikely)

2. The heat exchange in the radiator is lower than before,
a. either from parts being blocked in general,
b. a higher temperature of cooling air,
c. a lower flow rate of air (either dirt or slower fan operation).

3. The last possibility is that nothing is actually wrong, and the increase you see is caused by increasing ambient temperatures

[scoubix]

Originally Posted by kaiser

1. Reduced flow of water.
a.The thermostat does no longer open fully, and the flow through the radiator is lower than it used to be.
b. there is another part blockage of the flow, (oil cooler?)
c. The pump no longer pumps the same volume (unlikely)

2. The heat exchange in the radiator is lower than before,
a. either from parts being blocked in general,
b. a higher temperature of cooling air,
c. a lower flow rate of air (either dirt or slower fan operation).

Very valid ideas I'd say. 2b and 2c are however unlikely. Tests were done with ambiant temperatures of 10° to 14° (what we have currently here in France in the evening)

3. The last possibility is that nothing is actually wrong, and the increase you see is caused by increasing ambient temperatures

True, yet I believe I should not get these coolant temps with the very mild ambiant temps we currently have. I would accept it with 30°/35° summer temps.

[DMGRS]

I'd be changing the thermostat as a first port-of-call.

[scoubix]

Another thought came to mind. When I bought the car early last year, I had the auto box oil changed by the garage. I'm not that sure that the appropriate N402 oil was used, in spite of me telling the garage what oil to use. What if another oil was used, and causing the box to run at higher temperatures, the amount of heat from the oil cooler would be more important therefore causing the coolant temp to be higher than it should?
And don't get me started on "you should have made sure that proper oil was used" or "do the change now", I know already

[kaiser]

The oil will not make a difference, unless it is much thicker than the original.
I really don't see any problems that require any action at the moment, except keep an eye on the coolant and the temperature.

One thing you haven't mentioned is that the temperature sender can be slightly off. Next time the car is cold, check the engine temperature against the outside temp. If enough time has passed they should ideally show the same.

I know the outside temperature sender in my V8 shows 5 degrees too much for sure.

As for the oil in the box. I have run mine on Dexron II from Caltex. No problems at all, and I must be going for about 18 months now, I guess.
I use that in my 1.8T, the V6 and also the V8.

Goes to show!

[scoubix]

Originally Posted by kaiser

I really don't see any problems that require any action at the moment, except keep an eye on the coolant and the temperature.

Heck, that's what my friend and garagist has also told me today after discussing the thing with him for a couple of days. Says I worry too much, but should keep an eye on it anyway.

[kaiser]

I would listen to your friend and garagist!

Garagist...what a nice title!

It has a certain ring to it.

[SD1too]

Originally Posted by scoubix

Heck, that's what my friend and garagist has also told me today after discussing the thing with him for a couple of days. Says I worry too much ...

Hello Nicolas,

I agree with your garagist! There is nothing wrong with your cooling system. Mine varies too from the low nineties up to 100 degrees depending upon the load, road speed, ambient temperature, air con. demands, etc. etc. And yes, I have even seen mine sometimes rise slightly above 100 before the fan has an effect.

I think many people expect unreasonable stability from cooling systems. Coolant temperatures do vary, they always have done, but we haven't been aware of it with the mechanically damped gauges and more powerful engine-driven fans. Now that we have a digital readout, we start worrying, without reason!

Best wishes,

Simon

[scoubix]

Originally Posted by SD1too

Hello Nicolas,

I agree with your garagist! There is nothing wrong with your cooling system. Mine varies too from the low nineties up to 100 degrees depending upon the load, road speed, ambient temperature, air con. demands, etc. etc. And yes, I have even seen mine sometimes rise slightly above 100 before the fan has an effect.

I think many people expect unreasonable stability from cooling systems. Coolant temperatures do vary, they always have done, but we haven't been aware of it with the mechanically damped gauges and more powerful engine-driven fans. Now that we have a digital readout, we start worrying, without reason!

Best wishes,

Simon

Hey Simon

I guess you're right. If I didn't have the Intravee setup showing realtime coolant temp on my GPS monitor, I wouldn't worry. But then we all know that when the gauge starts rising, it's already too late too
Ok I'll stop worrying now, will just keep on monitoring it though, can't help it