So I've been battling to resolve a strange overheating problem recently, im beginning to think either im not bleeding it properly or its the HG failed.

Its a 300tdi disco 1 which seems to run spot on and most of the time the temp gauge stays still just below the half way point, however, you can be driving along and the temp gauge will suddenly start to rise beyond half way and the only way to bring it back is to turn the heaters on full blast then after a while turn them off and it runs normally again for a while until it happens again.

So far I've tried
- new viscous fan coupling
- ran with thermostat out (tested the thermostat working fine)
- replaced P gasket
- rad is already brand new
- re bleed the system by taking out the plugs in the thermostat housing and radiator filling until overflowing and replacing the plugs then running with heaters on
- replacing expansion tank cap (clutching at straws now I know!)


It does lose very minimal amounts of water, and has a bit of white smoke out of the back, only on acceleration though, my theory's are
- there is either a leak which I cant trace letting water out and air in creating an airlock
- im not bleeding correctly
- or HG failure which creates an airlock

Am I looking at a HG replacement? Or is there anything else I can try first? The strange thing is it seems to run perfectly in terms of power etc and it pulls like it always has done

joem93874 said:

Am I looking at a HG replacement? Or is there anything else I can try first?

Click to expand...

It appears you have looked at most avenues of possibilities, have you checked after one of these "overheating episodes" if in fact the coolant level has dropped, i.e. definite loss of coolant from the system, and is there gas pressure in the coolant header tank with low coolant level.
The rise and falling of your temp gauge will be due to the fact it's sender in the top front of the head/thermostat housing is an "immersion device" it cannot register accurately unless it is fully immersed/surrounded by coolant, the ups and downs are a result of vapour pocketing, i.e. it surroundings going from liquid to vapour and back again, lower temps registered at the vapour stage, higher as the liquid, which is superheated, (to near boiling at maximum system pressure) floods over it.
So, I have seen a 300Tdi running and driven with absolutely no coolant at the head level, blown the pressure cap off the coolant header, just gas discharging no coolant left in top of the engine at all, head absolutely smoking, temperature gauge sitting in the normal range, the owner said, temp on gauge went up, he slowed down the temp gauge went down so he kept driving for anther 10 miles, when he got to me it was still running on 2.5 cylinders and gushing combustion gasses out of the top of the header tank, head was absolutely stuffed, warped and twisted so bad impossible to re-surface.
There are three possibilities, 1/ There is a crack in the port areas of the head and coolant is being forced under expansion pressure into an exhaust or intake port and vaporised within the combustion process, but that normally will not be pressurising or rather over pressurising the cooling system as all the coolant is discharging into relatively low pressure areas.
2/ There is a crack in the combustion chamber area and the compression leaking into the water jacket is forcing out the coolant, at such high pressures of discharge even a miniscule leak amounts to a relatively large gas volume when it is discharged into the cooling system which works at only 15 PSI or thereabouts.
3/ And the most likely one, a head gasket leak into the coolant, most usually between cylinders 2 and 3, being a 300Tdi this, historically and unfortunately most probably will be the cause.
Prepare for a head gasket possibly head replacement.

Find the leak. Have the system pressure tested. If the head gasket was leaking into the coolant the system would pressurise PDQ. It maybe a leak causing a coolant void, that would give your problem.

the start of a head gasket issue, the system is difficult to fill and isnt prone for air locks

Take it from me as I have just gone through this. If you think it is the head gasket then deal with it before it's to late. If you cook the head to many times it will be scrap, £300 plus for a new head. To strip down and replace the gasket isn't to bad a job to do. Looking about £100 for parts and you will have to get the checked and probably faced, another £100. Mine done exactly as yours is doing, went on for a couple of months before it gave up the ghost. Used to get the white "steam" when I pulled away from junctions etc.

Hi
It could be as stated in earlier posts, but everyone forgets there is an engine oil cooler that plays a significant part in the cooling process.
Check when the two metal pipes that go into the right side of the radiator get hot. They should get hot before the top radiator coolant hose gets hot. If it is late in getting hot or is only cool or warmish it is probably your oil cooler thermostat that is part of the oil filter housing, that has failed or is failing.

Please find a list of parts for the repair you need

ERC5923 Thermostat for oil cooler
ERC5913 O ring for thermostat oil cooler
ESR1594L O ring for oil cooler hose, as it is a little easier to remove the hose to get at the thermostat adaptor

I cannot remember if there is a spring behind the adaptor / thermostat or not( I do not think so ???) it has been a whle since I did it, but as I was doing it the same time as an oil change/service I did remove the filter to give me slightly better access to the M6 adaptor bolts, but it depends if you go in from the side or from underneath
Regards
Jonathan

Not trying to question your knowledge or ability at all. So bare with me.

But are you absolutley certain it's over heating? Have you any proof other than what the gauge is reading in the vehicle.

I had very very similar symptoms a while back now on my 300tdi. Replaced similar things to you, and was asking the same question you are.

It turned out to be a poor electrical earth. Causing either acceleration or the heater to show an increase in temperature on the gauge. When in actual fact it wasn't. Months it took me to work out! Untill someone advised me as a last resort to clean up the main earth's. I'm glad I did, as it cost me nothing other than half an hours time. And stripping the engine!

The gauge now reads perfectly. So does the temperature

So a further drive over the weekend and the symptom is now as below

Drives fine at low speed low revs, anything over 2000rpm (motorway) will cause the temp gauge to start rising, turning on the heaters now doesn't seem to bring it down, it just sort of sits quite high on the gauge, then after a while it will creep up towards the hot end, near the red bit, so I stop, open up the thermostat bleed screw let out some air until water comes and the gauge instantly reduces back to normal (so im convinced its not actually overheating) you can then drive on for a bit until the air builds up again and you have to do it again

Off the motorway and at low revs (also when off road) it runs fine with no issues

A total of 100 miles on Saturday and it lost maybe a centimetre of coolant level from the expansion tank

So I think its HG or cracked head, but it is strange that it only happens on motorways or at high revs (up hills for example) I've rung and booked it into a garage to get it properly diagnosed, but they cant take it until Monday.

Fingers crossed its something not to bad!