300tdi slight overheating problems

Arierep · Feb 27, 2014

Hello,

The temp gauge on my 300tdi used to run just an air under the middle, everytime, any time.
2 weeks ago the water pump died on the run. It was quite fast, was driving at 60km/h when the auxiliary belt jumped off and I lost the alternator, PS and the pump. There was no time for the engine to overheat, as far as I know.

The pump was replaced ASAP, and everything seemed to be normal. Then, on a 15km spirited run, the temp gauge when a little over the middle, and stayed there. The interior of the car seemed to be a little hotter, but it could be my imagination. I stopped, as I was just arriving my destination. Next morning everything went like normal.

I did a few test runs, with no abnormal, over the middle temp gauge situations, and then some 200km, mixed city, B roads and motorway, also with no problems.

Today I was going on the motorway at 100/110km/h, when about the 17/20min mark the temp gauge jumped again past the middle, just a little, something like 3/5, and stayed there. I then proceded into some slow traffic and urban driving, and the gauge stayed there.

Is there any explanation for this? Is my engine overheating?
Thermostat problem?

Thanks

Landyfox · Feb 27, 2014

May just be the gauge that's faulty - mine has done this from day one, yet recording the temp with an infrared temperature probe its spot on.

THEengineer · Feb 27, 2014

have you bled it properly? and what condition is your radiator in? there are 2 bleed points on the 300 the rad and stat housing

Landyfox · Feb 27, 2014

THEengineer said:
have you bled it properly? and what condition is your radiator in? there are 2 bleed points on the 300 the rad and stat housing

If I'm honest I've only ever bled the water system by removing the cap of the expansion tank and allowing it to circulate a wee bit!!!!

Arierep · Feb 27, 2014

It was not me who changed the water pump and refilled the cooling fluid, so I can't be 100% sure it was bleed properly.

It is supposed to be:
- all caps opened
- fill radiator
- fill thermostat
- fill expansion tank

Right?

tottot · Feb 27, 2014

Yep,sounds like air in the system you nearly all ways need to bleed again to get rid of all of it.

Arierep · Feb 27, 2014

Why would air in the system only cause the temperature to raise in prolonged motorway use, and not so much in slow city traffic?

I'll try to bleed it tomorow, as well as stick a new OEM thermostat

THEengineer · Feb 27, 2014

Landyfox said:
If I'm honest I've only ever bled the water system by removing the cap of the expansion tank and allowing it to circulate a wee bit!!!!

ideally should be filled via the bottle,rad and stat housing if the plastic caps are shot get some 1/2 air vents from a plumbers merchants,they fit and easy to vent ,dont think the 300 is prone to airlocks but this is the way i filled mine everytime i done work on the cooling system

cowasaki · Feb 28, 2014

There was a top tip a few days ago which I haven't tried yet but basically...

Remove rad bung
Remove expansion bottle cap
Place rag around filler cap top and blow into bottle hard till rad bung overflows.
Replace rad bung
Remove filler bung
Place rag around filler cap top and blow into bottle hard till rad bung overflows.
Replace filler bung
Replace expansion bottle cap

Arierep · Mar 4, 2014

This issue is really messign with me.

Last Saturday I replaced the thermostat and bleed the circuit.
Whent for a motorway test and the car overheated to the last 1/4 before red.

I disassembled the thermostat and found that the new one took a lot longer to open, and was not opening as wide as the old one.

Slaped the old one back in place. So, old thermostat and bleed circuit.
When for a test and the temp gauge stayed right in the middle.

Yesterday I took the risk and when for a 150km trip, mixed motorway and mountain roads, some of them steep. The temp was in the middle the whole time.

Came back today, another 150km, steep mountain roads and motorway. first 50km the temp was right in the middle. Then I took a 5min stop for a coffee. Back to the car, I started it and noticed that the temp gauge was a little before the middle, something like 1/5. It stayed there for the last 100km, not moving an inch.

At the end I stoped the car, rested for 30min and went for a 10km short trip. The gauge stayed there, about 1/5 before the middle.

What is going on? First it overheats and now it is running too cool?

warrior · Mar 4, 2014

Sounds like you had some air in it,

Arierep · Mar 4, 2014

Can my gauge/send be shot?

warrior · Mar 5, 2014

Possibly, check it has a good ground 1st

Arierep · Mar 5, 2014

Any instructions on how to do that?
Thanks

warrior · Mar 5, 2014

Follow the ground to where it goes and check its a good clean connection

Arierep · Apr 5, 2014

So I ended up replacing the viscous unit.
It seemed to be alright after that. I took a few high speed motorway tests, at over 120km/h, with no overheating, as well as repeated slow traffic.

But yesterday, on a motorway with long climbs, it started to overheat again. I stoped imidiatly, cooled it down, and returned home by a B road at around 70/80km/h, without any further issues.

So, what to check now? Hoses? Radiator?
What would be the symptoms of a busted head gasket?

Thanks

warrior · Apr 7, 2014

Mines got hot last week, turned out my new thermostat was faulty

Arierep · Apr 7, 2014

My thermostat was checked and rechecked, so I got that covered

SteNova · Apr 7, 2014

viscous failing to lock?

Arierep · Apr 7, 2014

The viscous coupling is brand new

Any ways to check for a head gasket failure?

300tdi slight overheating problems

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