Overheating (but not always)

Afternoon,

I've got a strange problem on the mrs' disco 2 td5. It overheats but not on every journey. I drove 10 miles this morning no problem. On the return journey home a good few hours later the bugger overheated and got real sluggish. I turned the heater on full whack but no hot air. I pulled over, turned off, popped the lid and slowly undid the water expansion tank. The water started to boil so I realised it wasn't losing/using water. I started up after about 10-15 mins and the hot air started pumping out of the heater, real hot. The engine fan came straight on.

I'm not sure but I think the above indicates it might be a sticky thermostat. Does anyone have any advice on checking anything else?

Thanks

I'd agree with you on the thermostat, it sounds like it's sticking.
Griff

could indicate head gasket or even cracked head,

Similar experience with mine:
Check the cooling system has been bled properly and consider changing the expansion bottle cap
Check / change the thermostat (which only opens after driving at > 2500 revs for a while)
Check for leaks to the heater matrix
Hope the top hose isn't pressurising as it might then be the head gasket!

headtester said:

check the cooling system has been bled properly and consider changing the expansion bottle cap
check / change the thermostat (which only opens after driving at > 2500 revs for a while)
check for leaks to the heater matrix
hope the top hose isn't pressurising as it might then be the head gasket!

Click to expand...

+ 1 ....those bolded parts you must do asap

easiest thing to check first is that their is no air locks, then work your way through the above list

Check the drive on the water pump mine was chewed by the power steering pump so was slipping. it was ok taking it steady but not able to cool enough on long journeys.

A air lock would give you the heater problem so I'd bleed the system first
And if there's no change then check the thermostat
And so on

Mine was exactly the same when the head gasket went

On your return Journey was the engine under greater load ie steep hill? that when mine overheated

I've got exactly the same problems, so far I've had the HG tested
and all came back clear- quite normal apparently.
Had a new rad,waterpump and thermostat: still have the same probs!
I'm gonna disconnect the matrix if it still over heats then I have to
Accept that it's the HG
Sorry to say but I think we have the same problem
everything I've read it's supposed to be because of the weak plastic
dowels between the block and head

IMO the HG failures might have other causes too... the fact that many owners dont give a sh*t about that electric engine cooling fan(so named aircon fan), most of owners dont know that the electric fan is there to help the viscous fan when the engine works at extreme temperatures, that's it's main purpose not to help the aircon... that fan kicks in at 110*C to help cooling, without it the Td5 works quite often between 110 and 120*C and the gauge will leave the middle only above 125*C...i've tested that with hawkeye on live data for days (summer time off course) cos i replaced the viscous fan with an electric one and i can confirm that...the gauge was at the middle all the time but the temp was between 119 and 105 according to speed... i refitted the viscous fan then everything came back to normaln i mean it never exceeded 110*C

so IMO on a long run that temp. range would 'tenderize' the HG and it will fail sooner...also the practice with removing the viscous fan for winter doesnt seem the best for me especially if you tow something or drive it more under load... you'll expose the engine to high temp.'s without even knowing it

Cooling fan request
The A/C fan request is an input to the ECM from the ATC ECU to request that the engine's electric cooling fan is
activated to provide additional cooling for the A/C condenser.
The cooling fan relay is located in the engine compartment fuse box and is also controlled by the ECM. It is a four pin
normally open relay. This means that the relay must be energised to drive the cooling fan. The cooling fan is used
especially when the engine is operating at excessively high temperatures. It is also used as a part of the ECM backup
strategy if the ECT sensor fails.

Click to expand...

it would be interesting to see how many of the owners who experienced HG failure did or didnt have this fan in working order ...or if HG failure is most common on the cars without aircon

... just something to think about, i dont want to start a debate on this but IMHO a not properly working cooling system could be the cause of a HG failure in time without any other reasons ..., more often that some locating dowels which are important untill the head is well tightened after that they have no use there....see the attachment too

Hi

Sierraferry is totally correct in what he says. There is also a similar but much less sophisticated set up in Disco 1 with AC. ie a "cut out" switch that switches off the AC compressor but allows the AC fans to still run when it is hot, too give the extra cooling when required .

Regards

Jonathan