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[Kevin Wood]

102 degrees is not hot enough to blow the rad. cap so you must have either air introduced to the cooling system by, for example, a head gasket failure, or poor circulation of the coolant causing localised overheating and boiling of the coolant inside the engine, while the ECU sender is seeing slow moving coolant at a reasonable temperature.

My money is on the latter. At 90 there is so much airflow through the rad. that the engine should get as much cooling as it needs IF it can circulate coolant fast enough through the rad. The fact that the heater makes a difference in this case is key, because it probably promotes just a little more coolant circulation through the engine. Ordinarily a rad. moving through the air at 90 would lose way more heat than a little heater matrix.

Problem is, if the circulation is poor and it's not improved by flushing it may be a head off job to investigate. If there are dodgy deposits visible in the engine it does start to look like there's something clogging the water jacket up.

Kevin

[TheBoy]

Another theory, and I am thinking out aloud here, is the main inlet and outlets are at the front.  One heater pipe is at the rear.  Could it be the rear cylinders are getting insufficient cooling due to coolant flow there being poor, and by turning on heater is causing more circulation at the rear?

The ECU temp sensor reads 2 or 3 degrees warmer than the dash sensors. Not sure if this is just tolerances, but the dash one is near cyl 2, ecu one is near cyl 4.....


Hmmmm.....


Whatever, I still have no idea how to resolve...

[Dazzler]

It seems that you have changed most things and flushed etc........So my theory is if the whole water system is getting hot evenly(no cold or really hot spots) then the fault must lie with the headgasket allowing slight pressuring of the water system
I have had 1 car over the years that was fine with normal driving around but after 10 mins at above 70mph would start to overheat. That in the end turned out to be the headgasket....but not found until i had changed everthing else mind you

[TheBoy]

Right, Mrs TB has mentioned something.

Is the readings from the ECU's damped? I know the instrument one is, but the engine one?

The readings tend to go up after the event by a few seconds...   :-/

[TheBoy]

It seems that you have changed most things and flushed etc........So my theory is if the whole water system is getting hot evenly(no cold or really hot spots) then the fault must lie with the headgasket allowing slight pressuring of the water system
I have had 1 car over the years that was fine with normal driving around but after 10 mins at above 70mph would start to overheat. That in the end turned out to be the headgasket....but not found until i had changed everthing else mind you

Problem is, every diesel HG I've seen fail, boy do you know about it....

[Kevin Wood]

Another theory, and I am thinking out aloud here, is the main inlet and outlets are at the front.  One heater pipe is at the rear.  Could it be the rear cylinders are getting insufficient cooling due to coolant flow there being poor, and by turning on heater is causing more circulation at the rear?

Normally with this kind of setup the holes in the head gasket are sized from front to back to equalise the temperature throughout the engine, as far as possible. You'll have small coolant holes between head and block at the front because you've already got lots of water flowing past these areas to the back of the engine, and you're close to the pump with lots of coolant pressure. You'll have bigger holes at the back of the engine to promote an equal cooling effect back there.

So, in an ideal world, it shouldn't make a lot of difference but bung some of the holes / waterways up with radweld / eggs or use a cheap head gasket with the wrong size holes and it's a different story. It could be that there's a problem with flow to the back of the head and that the heater promotes a little more flow which helps matters.

Kevin

[wombatcurry]

I'm sure you're generating too much heat or not losing enough of it - neither of my TDs ever get that high (albeit on the dash guage) - the old one runs around 92 constantly (95 thrashing up telegraph hill), the new one seems to run at approx 80 occasionally rising to 90 max.

If you're sure that the cooling system is in order (ie you're losing heat correctly), it's time to start wondering where extra heat could be coming from. Sorry to say it, but HG??

[TheBoy]

Yeah, I am at a loss to work out whats wrong.

I am beginning to wonder if head has to come off to check for bits of old pump or other blocakge.  However, that is not a task I can tackle on my own

[Martin_1962]

Well you have lots of friends so ask for help!

[Kevin Wood]

I am beginning to wonder if head has to come off to check for bits of old pump or other blocakge.

Only other thing I can think of is to give it a flush with something much more aggressive than you have previously tried. This could afford to be a kill or cure step if the only other option is removal of the head. Something that dissolves limescale maybe? Dishwasher powder or acid? Remove the heater matrix and rad. from the circuit by bypassing them with hoses, fill it, run it up to temperature a few times and then drain and flush with a hose straight away to prevent prolonged contact with the internals. Might be worth a shot  :-/

Is the turbo water cooled? Just wondering if the connections to that are blocked? Then again, it wouldn't contain enough water for it to blow the cap if it suffered localised boiling, I'm sure.

Kevin

[TheBoy]

I am beginning to wonder if head has to come off to check for bits of old pump or other blocakge.

Only other thing I can think of is to give it a flush with something much more aggressive than you have previously tried. This could afford to be a kill or cure step if the only other option is removal of the head. Something that dissolves limescale maybe? Dishwasher powder or acid? Remove the heater matrix and rad. from the circuit by bypassing them with hoses, fill it, run it up to temperature a few times and then drain and flush with a hose straight away to prevent prolonged contact with the internals. Might be worth a shot  :-/

Is the turbo water cooled? Just wondering if the connections to that are blocked? Then again, it wouldn't contain enough water for it to blow the cap if it suffered localised boiling, I'm sure.

Kevin

Turbo is air cooled.

I should have some Forte arrive in next day or so, see what that does.  Already tried bleach (I'm getting desperate!), also screenwash is supposed to be a cure for all ailments, though have to be careful as its flammable!

Keep the ideas coming

[TheBoy]

Well you have lots of friends so ask for help!

Thank you for kind words

I am, however, very concious of putting out many members friends here already, esp M_DTM, LB66, Tunnie, and JamesV6CDX  

[Martin_1962]

Well you have lots of friends so ask for help!

Thank you for kind words

I am, however, very concious of putting out many members friends here already, esp M_DTM, LB66, Tunnie, and JamesV6CDX  

Do you think the two Marks, Dave and James would mind - you host and look after the forum, you do Tech2, I don't think they would mind at all - I will ask my dad if he knows of this problem (retired BMW mechanic).

I know that James has already offered help - I think too many people would get in the way. Who here is the TD expert?

[wombatcurry]

Damned shame I'm not in England at the moment - I'd have liked to have given you a hand (would have been a good learning exercise for when/if  have to pull a head).
Good luck with it - I'm sure you'll let us know.
Are you supposed to replace head bolts when you undo them - I spotted a set on ebay a few days ago that might be of use.

[TheBoy]

Just another idea...

Seeing as the stat is on the coolant inlet, if the radiator was cooling too much, would that cause stat to close, hence hot engine?