Def 110 TDi 300 overheating

Hi all, I'm having a cooling problem with my wife's '96 Def 110 TDi 300. She overheats, according to the gauge dramatically after a short drive.

Symptoms:

1. Coolant temp gauge shows overheat very quickly after a short drive;

2. Header tank coolant stays cold, but rubber hoses are hot from the 'stat housing to the rad;

3. Rad is warm at the top but cool at the bottom;

4. No smoke or steam from the exhaust or anywhere else;

5. No apparent loss of power;

6. No loss of coolant;

7. No pressurisation of the header tank;

8. Squealing noises coming from the new water pump, unless I remove the header tank cap and the 'stat housing cap, then they stop. It's as if there is insufficient coolant going through the pump until these caps are removed?????


Up to now I have:

1. Flushed the rad, the heater rad and the block;

2. Replaced the water pump;

3. Replaced the 'stat;

4. Replaced all hoses and clips;

5. Refilled with new coolant ensuring that the rad, the stat housing and the header tank levels are all good.


It feels like an air lock to me, but I'm out of ideas to fix it. Anyone got any inspiration?

Could try parking facing up hill and just let it idle with the cap off and then once it reaches temp so the stats open shut it off and fill up, then do it again to make sure

If not you sure its not the gasket just starting to go ?

Dr_evil said:

If not you sure its not the gasket just starting to go ?

Click to expand...

Thanks very much for the replies.


I'm hoping it's not the head gasket and I can't yet see any signs of it being that?

What I might do it to park it uphill with ramps on the front and see where we go.


However that doesn't answer why it started doing this out of the blue?


Just off out to buy some more coolant.

Well if it was just out of the blue are you sure that a) your coolant is at the right mix and you didn't overdilute it during winter and b) your fan is still working



If not then I'd suggest head gasket, can always get a sniff test done to make sure

sounds like rad is buggered if top hose is hot but rad isnt hot all over core ,is very common,rad fills and empties on the same side and the coolant tends to drop striaght down and out without going through all of core

jamesmartin said:

sounds like rad is buggered if top hose is hot but rad isnt hot all over core,is very common, rad fills and empties on the same side and the coolant tends to drop straight down and out without going through all of core

Click to expand...

So bearing that in mind, why doesn't the coolant in the header tank warm up at all - it remains absolutely cold? Doesn't pressurise at all.

I've just checked the small bore pipe that goes from the stat housing to the 'Y' joint, then on to the header tank and than seemed ok. I also checked the other small bore pipe that goes from the 'y' joint to the top to the rad (drivers side)and that seems ok as well.

If it's the rad then so be it, but I did flush it out until the water ran clean. I also flushed out the heater rad - which appeared to be blocked, but eventually ran clean.

I'm short of bread at the mo' so I don't want to go spending dosh, if it doesn't fix the problem.

Any other ideas?

Dave

Faulty temp sender or gauge ?

Dr_evil said:

Well if it was just out of the blue are you sure that a) your coolant is at the right mix and you didn't overdilute it during winter and b) your fan is still working



If not then I'd suggest head gasket, can always get a sniff test done to make sure

Click to expand...

I didn't need to touch the coolant through winter but when I flushed it out of the cooling circuit there wasn't too much muck there. And yes, the fan is working fine, although the engine should still easily keeps it's cool without one, if all else was good.

Dave

Dr_evil said:

Faulty temp sender or gauge ?

Click to expand...

Well I wondered that so I pulled the wire off, with the ignition on and the gauge just dropped to the bottom, so I think the gauge is ok.

But I faulty temp sender wouldn't stop the water in the header tank from warming up, would it?

I'm going to find a darkened room and lay down

rad does need to be hot all over to cool engine ,flushing rarely works ,does litte bleed pipe to header tank have flow from it ,is new pump actually pumping

jamesmartin said:

rad does need to be hot all over to cool engine ,flushing rarely works ,does litte bleed pipe to header tank have flow from it ,is new pump actually pumping

Click to expand...

Thanks for coming back to me James. The new pump is definitely pumping - I took off the small bore pipe from the stat housing and flicked the starter and coolant shot out.

When I removed the little pipe at the header tank end (without the engine running) coolant did flow, but not under pressure.

I've also just checked the coolant flow diagram to ensure that I put everything back in the right order.

If theres no pressure build up that could possibly be the temp gauge or sender then I know you tested it but even if it was HGF or something serious the I'm sure the header should pressurise shouldn't it ?

Have you considered running it to temp then using a thermometer to check the temp ?

Dr_evil said:

If theres no pressure build up that could possibly be the temp gauge or sender then I know you tested it but even if it was HGF or something serious the I'm sure the header should pressurise shouldn't it ?

Have you considered running it to temp then using a thermometer to check the temp ?

Click to expand...

If it was HG then normally you would get: pressurisation and or steam and or contaminated oil - and to date I have non of these.

What it feels like is a lack of circulation of the coolant and all I can think of is the rad, but I still don't get why the header tank coolant remains stone cold - even after the 'stat has obviously opened and you can feel the hot
hot coolant running into the rad.

I hadn't considered measuring the temps, principally because they are so obviously different. But thanks for the suggestion and your interest.

If I had some beer in the house, now would be the time !!!!

Dave

That thermometer things the only thing I can think of really just to make sure its definitely not the temp sender as I cant see the rad suddenly failing like that but then again who knows ?

Outside of the rads not been caked in **** through winter has it ? could always wash it with a low pressure hose to get crud out from between the fins

Dr_evil said:

That thermometer things the only thing I can think of really just to make sure its definitely not the temp sender as I cant see the rad suddenly failing like that but then again who knows ?

Outside of the rads not been caked in **** through winter has it ? could always wash it with a low pressure hose to get crud out from between the fins

Click to expand...

No the rad is clean both sides. I don't get it either, but I can't get past this business of the header tank remaining cold,even when the coolant in the other parts of the system are very warm ???

Are you sure the thermostats opening ??

Sounds like an air lock to me, have you been filling the circuit back up via the silly plastic screw on the thermostat that usualy breaks ?? Have you unscrewed the other one on the top of the rad that also usualy breaks ??

Is the heater blowing hot air out ?

Jason2 said:

Are you sure the thermostats opening ??

Sounds like an air lock to me, have you been filling the circuit back up via the silly plastic screw on the thermostat that usualy breaks ?? Have you unscrewed the other one on the top of the rad that also usualy breaks ??

Is the heater blowing hot air out ?

Click to expand...

The heater blows hot air consistently.

I refilled the coolant via the header tank initially, then checked via the rad plug that it was full and finally via the stat housing plug - both silly plugs now replaced with radiator valve caps.

Cheers
Dave

Bugger !

Faulty expansion tank cap ?

Are there signs of over heating or is it just the gauge going in the red ?

Jason2 said:

Bugger !

Faulty expansion tank cap ?

Are there signs of over heating or is it just the gauge going in the red ?

Click to expand...

Header tank cap - if it was faulty and was letting the pressure out, then the system wouldn't pressurise a little at it should (to 15psi if memory serves me right?) and so reduce it's boiling point. That would mean that the coolant will boil at a lower than is normal temp, which might fool the temp sensor?????


All I've been able to find up to now is:

Top hose hot;

Top of rad hot - bottom cold;

Header tank cold

Heater hot

No steam or white smoke

No mayonnaise or obvious oil contamination.

No loss of power.