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Old 14th March 2021, 13:45   #1
paulh260260
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Default Overheating?

Guys

Just swapped out a failed three speed fan for a two speed with gold resistor it passed the demist test and road test kicking in at 100 degrees however...

On a road test today around the M60 , 40 miles at a steady 70 mph the temperature seemed way too high settling between 107 and 110 occassionally hitting as much as 113 on inclines.

I've checked for obvious leaks but none can be found and the header tank has only dropped from just above the fins to just below them.

Far more worrying is the chocolate milkshake in the oil cap and cylinder ( see piccies)

This does not look good to me, is this a sign of impending engine failure?

What should I check to determine what is causing this and is the overheating seperate issues or connected, or even the cause?

Its an 02 2.5 V6 petrol connie BTW

Paul
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Last edited by paulh260260; 14th March 2021 at 13:53.. Reason: add more details
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Old 14th March 2021, 14:01   #2
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You can get mayo deposits in certain damp conditions -and HGF on the V6 is comparatively rare.

It does sound like your new fan is not kicking in for the temp to get that high.

I would give her a good 10 miles at good speed- leave overnight - open the expansion tank - if there is a clearly audible escape of gas/smell of exhaust gas in the expansion tank this would point to exhaust gases having entered the coolant system there should be no pressure in a cold system.

Also on the V6 a faulty oil cooler could cause oil and coolant to mix causing Mayo so it maybe this at fault.

As an aside - i gather you filled the coolant to the top of the fins - as folk will advise on here that is too much - should fill to the max mark at the bottom of the tank or a few mm's higher to the foot of the fins.
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Old 14th March 2021, 14:16   #3
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Quote:
Originally Posted by Yorkshire GOC View Post
You can get mayo deposits in certain damp conditions -and HGF on the V6 is comparatively rare.

It does sound like your new fan is not kicking in for the temp to get that high.

I would give her a good 10 miles at good speed- leave overnight - open the expansion tank - if there is a clearly audible escape of gas/smell of exhaust gas in the expansion tank this would point to exhaust gases having entered the coolant system there should be no pressure in a cold system.

Also on the V6 a faulty oil cooler could cause oil and coolant to mix causing Mayo so it maybe this at fault.

As an aside - i gather you filled the coolant to the top of the fins - as folk will advise on here that is too much - should fill to the max mark at the bottom of the tank or a few mm's higher to the foot of the fins.
Thanks for that

Yep there has been a hissing when I opened the header cap but I put that down to an airlock whilst it was running without the fan and being topped up. I bled her yesterday and it seemed fine but I haven't ran her let her cool then opened the header tank.

Ill give her a quick blast later the leave her overnight and check for gasses leaking in the morning i ll also give it a sniff the see if its exhaust gasses.

As for the fan speed as I say it passes the demist test and kicks in at exactly 100 degrees, so I don't thinks that the problem!

Cheers

Paul
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Old 14th March 2021, 14:33   #4
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Quote:
Originally Posted by Yorkshire GOC View Post
As an aside - i gather you filled the coolant to the top of the fins - as folk will advise on here that is too much - should fill to the max mark at the bottom of the tank or a few mm's higher to the foot of the fins.
You can see the MAX level step at the bottom of the tank.
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Old 14th March 2021, 14:47   #5
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You can see the MAX level step at the bottom of the tank.
I must admit to overfilling the header to avoid losing too much coolant while the low speed fan was inoperable.what if any damage could that cause?
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Old 14th March 2021, 14:57   #6
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Overfilling will just cause coolant to be pushed out of the tank via the vent so long as it is clear.

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Old 14th March 2021, 15:21   #7
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Overfilling will just cause coolant to be pushed out of the tank via the vent so long as it is clear.

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Vent?do you mean what Haynes refer to as the bleed hose?
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Old 14th March 2021, 16:32   #8
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Vent?do you mean what Haynes refer to as the bleed hose?
Basically it comes out via the pressure relief valve in the cap.
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Old 14th March 2021, 16:52   #9
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Quote:
Originally Posted by stevestrat View Post
Basically it comes out via the pressure relief valve in the cap.
If the pressure cap is faulty could that cause overheating?
I've got a spare, maybe I'll swap them out and see what happens
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Old 14th March 2021, 17:40   #10
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As Steve says " Basically it comes out via the pressure relief valve in the cap."


If you fill the cooling system much higher than the max. when cold, even possibly to the bottom of the neck, there is no airspace for the coolant to expand into as it gets hot, as pressure increases to above the cap pressure the valve in the cap will lift to vent the pressure and water.


This can give the impression that there is a loss of coolant, which there is, but the coolant lost is the excess when overfilled, venting as it should and when re-checked when cold it will be around, but more likely just above the the max.


If there is antifreeze in the coolant there should be evidence and stains of this around the bottom of the cap, where it vents and possibly around the engine bay if it vents whilst being driven.


Can a faulty cap cause overheating, possibly for two reasons, 1) if there is a substantial loss of coolant which there doesn't appear to be, 2) if the cap can't maintain pressure as the system gets hotter approaching boiling point, the water needs to be under pressure to prevent the water from actually boiling and causing steam pockets around the hottest area, cylinder head and particularly the ex. valve area, but you would expect to see evidence of some steam or water loss from the faulty cap.


The remaining popular o/h causes are faulty thermostat, system not correctly bled on refill, blocked radiator core ( unlikely ) rad fan or rad fan sensor faulty, cyl. head problems.


The mayo you have in the oil cap can come about simply with lots of stop start short journeys but can also be a sign of head, or head gasket problems, there may not be the usual evidence of steam from the exhaust when hot with a small leak due to the heat of the cat turning it into superheated steam which won't be visible.


If it was me I would initially satisfy myself that there are no head gasket problems, first by getting a friendly garage to use a sniffer test to see if there are combustion products in the coolant, plus you can purchase, quite cheaply, some DIY kits, if you are then satisfied that the gasket/head is OK you can then progress to sorting the apparent overheating problem.


Finally, don't forget, that the engine may not actually be overheating, a faulty temp. sensor / gauge could be showing higher than actual readings.
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