300TDI overheating

[dero]

Having trouble with my 95 defender 300TDI.
It warms up & starts to overheat after aprox 15km at road speed .
Radiator was replaced aprox 20k ago, water pump aprox 10k ago .
Since having the recent trouble I have replaced the t'stat & bottom rad hose [ it had signs of ware from the top pulley , so replaced it to eliminate any doubt ] .
Cant see any sign of leaking anywhere .
When I remove the t;stat housing plug there is always air in it & needs topping up . I presume the overheating is because of the air, but don;t know why .
Any help would be much appreciated .

[justinc]

Does your heater get warm at all?.

If not or if is warm and goes cold after spirited driving and there is also excessive pressure in the expansion tank i would lean ever so slightly toward a leaking head gasket....

Also. Is it actuallygetting hot? The defender temp gauge can rise alarmingly due to poor earthing etc.
Jc

[AlecW]

There could be an airlock in the head and coolant needs to be bled to remove air pocket. However if the coolant has pressurized air coming out after running it for a while you may find it's a head gasket\warped head (exhaust gas pressurising the coolant system) from previous overheat.
Lets hope that isn't the case as expensive to fix. I have done 2 and same symptom.

Take to a mechanic and get them to do a pressure on coolant system 1st and see what comes back. If you have done a gasket there's a high chance the aluminium head has warped and needs to be skimmed, valves reground. This process of pulling apart, pressure testing head, skimming and valve re-seating (providing the head is still viable) and refittment is a costly exercise. Do not run it until is diagnosed as overheating a 300tdi is bad juju.

If you undo expansion tank is there air that rushes out after running it?

[dero]

heater has been bypassed for some time & if run to as hot as I dare, aprox 3/4 on the guage , the expansion tank boils over when the cap is cracked open .
Head gasket ?

[AlecW]

Head gasket mate. I feel for you, I really do....

[AlecW]

Looking at couple hours to get head off, then prob $200+ for pressure test/skim head. If head ok and can be skimmed then new headbolt set and correct tolerance gasket ie piston protrusion from head deck (Elring composite), manifold gasket and maybe rocker cover gasket then about 6hrs+ to refit and do valve clearances.

If need new head set then around $1300 for kit. I got maybe 8000km after skimming before mine went again so got a turner performance head from the UK.

It's about $2700 if you need a new head or around $1600 if can salvage existing going through mechanic in my exp. Obv this is a give or take thing but just to give you a idea for lack of surprise

[PAT303]

I'd replace the fan hub first. Pat

[TonyC]

heater has been bypassed for some time & if run to as hot as I dare, aprox 3/4 on the guage , the expansion tank boils over when the cap is cracked open .
Head gasket ?

The heater is part of the cooling circuit.
You can't just block the heater hoses, you must run a loop of hose from the outlet on the motor back to the inlet on the motor.

Tony

[AlecW]

I'm pretty sure that's what he means by "bypassed". Didn't say blocked. The fan hub would not account for expansion tank burbling after running it.

[PAT303]

It would if it was getting hot because the hub is U/S. Pat

[rick130]

You have to be a little careful reading too much into the expansion tank cap opened when hot as any vehicle will bubble over with the sudden decrease in system pressure.

It needs to be cracked and then observed for bubbles when the system has settled.

You can also do a combustion gas test on the cooling system if you aren't sure.
Have done this on my 300Tdi a few times when it's been a bit too hot for my liking.
Luckily it was OK everytime, including blowing the header tank on the heater when climbing a range.
I really thought I'd done the head and h/gasket that time as it pumped most all the coolant out of the system.

As Pat said, the Defender really needs the fan clutch working properly too, ram air isn't enough to overcome the underbonnet air pressure at speed.

[dero]

Thanks for the replies , I will get the test done to check for ex. gas .
Yes the heater was looped out properly .
I will replace the fan hub with a known good one .
Should know more in a week or so .

Thanks to all .

[AlecW]

There is a couple ways you can check if the viscous clutch is working correctly. If you need to replace will need a long skinny spanner to get in there. A little expansion when opening the cap is normal but if it burbles for a prolonged period I would still be inclined to think head (propensity for 300's to do them and vehicles age)


Hopefully it is just fan hub but I would be surprised. Get it up to operating temp and then roll up a magazine or news paper and gradually push it into fan from behind. If it resists and starts to shred paper you have a good idea if it's engaged for the most part. If it just stops without much of a fight then then viscous unit is US. Even just rev it at fuel pump and feel if it increases air flow with higher rpms. Or if engine is cool, rev it with cap off expansion tank and watch if stream of bubbles come rushing out.

[dero]

Replaced the fan today , with a good one off another landy .
Joy of joys , gave it a good workout and all OK .
Thanks for all the advice .

[AlecW]

Replaced the fan today , with a good one off another landy .
Joy of joys , gave it a good workout and all OK .
Thanks for all the advice .

That's fantastic mate, great to hear. Dodged a bullet there!