overheating 300TDi 110

[Ollie]

Laila is getting very hot, an a motorway at 50mph I just manage to keep her running under the red.
As I slow down, she then starts to cool down, the faster I go, the hotter she gets.

I've just stripped out the water pump and thermostat, both look nearly new, but I have replaced them anyway. This obviously isn't the route cause of the overheating, so then what is????? :(bigshock):

There's no water leak, I replaced the 'P' gasket a few months ago and therefore the coolant has been replaced, the oil and filter are changed every 5K miles, and there's plenty there. I've had the rad out and flushed it through with the hose, so no blockages, and it's in good nick.

The only thing I have done is add a full length intercooler, but this was done months ago, and she's covered a few thousand miles on and off road since then. I didn't up the fuel pump pressure, but I'm told diesels run cooler with a weaker mix.

So, I throw it out to the panel, any suggestions?

Cheers
Ollie

[Thrasher]

Take the oil filler cap off and listen - is it chuffing?

When the head went on my old Granada it was exactly the same as you describe :( Would run all day under 50...but take it over that and up went the needle.

[Ollie]

Neil,
I have looked at the oil filler cap, and I would have thought that there would be some discolouration or white foam, but its clean?

She's in pieces on the drive at the moment, I'll get her back together this eveing and check for 'chuffing'.
I hope it isn't, that's a rather expensive repair :(bigcry):

Ollie

[Ollie]

Could it be the Viscous fan? Can these fail? Is there anyway to test it?


Ollie

[ChrisW]

The viscous fan is a possibility however I have experienced similar with my 300 in a Disco and understand that the viscous fan is useful upto about 30-40mph, above this speed and the air is forced through the rad quicker than the fan could pull it through anyway which kind of stuffs that theory altogether!

I have also heard that the radiators can block up/rot internally over a few years and either a recore or replacement is the only option.

What kind of off roading has it had? I 'back hosed' (hose pipe and flush through the rad fins from the engine side out) mine and probably got about half a bucket full of sand/silt - easier if you can do it with the rad off the car.

DON'T try and pressure wash the rad - you'll just bend all the fins over and stuff it completely!

[EvilEd]

As you have said it's only over 50 that it gets hot, it HAS to be flow related. Start with the rad, put a torch down the back and make sure you can see the beam through it all over. if not, take it our and hose it both directions, then go back 20 mins later and do it again once it's softened up a bit.

If it still does it, check for "Cool Spots" on the rad.... run her around for a bit and then turn it off and feel round the rad.... any cool spots suggest a blockage.... (Obviously start with a cold engine), Try a Rad Flush, but best thing is a re-core or replacement rad.

Replace the thermostat... it's worth doing for a few quid. (You can test in a saucpan id you know the open and close temps and have a jam thermometer... but you may get a slap for doing it :)

Make sure the heater is on hot when you fill her up..... May sound like I'm teaching you to suck eggs, but easily forgotten. Air in the system can cause all sorts of problems.

Lastly, water pump.... any canary's under the bonnet?

How fast does she cool when you stop.... does the needly drop rapidly down to normal, or take ages?

[defenderdan]

You said that you flushed the rad out but did you do the engine, there could be a blockage in there. Take the thermostat out then put the thermostat housing back on. Then drop your top and bottom rad hoses off and run your hose through there.

[Hangover]

Take the front grill off and check wether the radiator is warm all accross the matrix(no cold patches),if in doubt replace radiator,don't bother flushing it because it's usually a waste of time.
Kev

[drum]

I have very similar with a car, that turned out to be air trapped in the system. Repeated bleeding through the little bleed screw in the flexible hose, and squeezing al the air out eventually cured it.

[Ollie]

After replacing the thermostat, water pump and drive belt, the problem has gone, (hopefully). I filled the system making sure the heater was set to hot.
Taken her for a blast for 20 mins, running beautifully.
Cost me £45 in parts, but worth it for peace of mind.
Maybe it was only an air lock?

Cheers Guys
Ollie