300Tdi cooling problems

[DefendersRock]

Hi guys,

Well I'm on a loss.  I've been having cooling problems with my '95 Defender 300Tdi for almost a year.  I flushed the system many times and ran several rad flushes through the whole system.  I replaced the water pump, fan coupling, thermostat, sensor, vent hoses/y-piece ejector and had the radiator re-cored.  It's still overheating and I'm running out of ideas.  It can idle all day and be fine...  It's only when I'm up to speed (especially highway speed) that I overheat. 

The only thing left I can think of is rad cap, worn out bottom hose (collapsing when hot?) or a blown head or head gasket. I'm not sure what the symptoms would be for these.

Anyone had this problem before?
Derek

[Rosco]

Are you getting hot air out of the heater? have you still got the fan shroud in place?

Is it using any coolant? that could point to a leak or a head gasket issue if there is no visible traces of a leak.

Any idea how hot its getting? could it be the factory gauge reading strangely, on one of my trucks it was overheating on the dash gauge, but when I scanned from the OBD the temp it was fine, but the factory gauge heads towards the red far quicker than the OBD data was showing.

[DefendersRock]

yep still getting warm air from the heater.  and yea the fan shroud is in place.

i haven't' noticed any loss of coolant through this whole thing.  i've dumped the system many times in the last few months though so if it was a slow leak i may not have noticed.  i've never needed to top up once filled

it's definitely getting too hot.  the rubber seal on the thermostat plug (only a few months old) is warping and breaking down.  The seal on the rad plug is the same age and is fine.

[Rosco]

Might be a silly question, but is the rad getting really hot?

[Red90]

When it has overheated, is the bottom rad hose hot?  This would show whether or not the coolant is pumping properly.

Is the viscous unit locked up or loose?

Maybe grab an IR gun and verify how hot things really are to make sure it is not just the gauge.  I have one you could borrow.  I could probably help you look at it if you like.

[Matt H]

Are the hoses pressuring up more than they should? Are you blowing hoses? Is coolant pucking out of the headder tank?

[DefendersRock]

Not blowing hoses or having coolant bubbling out of the expansion tank (even with the cap off).  Thank god

The top and bottom hoses are warm to the touch.  The top would probably be hot if the fan wasn't blowing air on it.  Not sure how to check if the rad is hot

Red - thank you so much.  I'll likely give you a shout next week

[Red90]

If it is really overheating and the pump is moving coolant through the rad, the hoses would all be too hot to touch.

[Low-Range]

You did not say if the viscous fan has been checked/replaced...that's what was wrong with mine.

[Darkdevo]

I had overheating issues with my 300tdi then I took rad in to be checked he noticed between the top inlet and bottom inlet there is a hole that joins the 2 inside the rad. The wall, so basically instead of the coolant getting pushed through the rad core fins and back into the engine, it was just circulating through that hole and not going through the rad.  It looked like a stock hole from factory but my rad guy said no that's dumb. And blocked it off since then it's been running like a top 3yrs running.

sent from darkdevo/Bill.

[Red90]

He had the rad re-cored locally.

I met up with him and had a good look.  It appears the problem all along was the gauge.  All of the actual temperatures were perfectly normal when the gauge was reading high.  My suggestion was to get a new VDO gauge and sender.  Run a dedicated wire from the gauge to the sender and check all grounds.

That said, the design of the 300TDI cooling system is horrible.  A big step backward from previous models.  I had never really looked at it before this and was amazed at the multiple poor decisions in the design.

[Darkdevo]

Ic ic .