300tdi cooling issues

[Reiny]

My 300tdi has been fantastically reliable for the past 9 years however I have been plagued with a spate of cooling related problems. The engine has never overheated however it's only because I keep my eye on the temperature gauge and am a stickler for maintenance. So far I have replaced everything related to the cooling system (some items have been replaced more than once). Anyway, yesterday I was driving home and the temperature needle sat at just over 90 degrees. It usually climbs to 90 on 2 particular hills and goes down to 80 or 85 degrees as soon as the hill levels out. In a haste to get home I gunned the engine on a 100 metre stretch of road and the needle climbed a tad higher (never touched more than 95 degrees),then it went back to around 85. Popped the hood to have a look and nothing seemed to be out of the ordinary. I was a bit concerned however that the top hose wasn't as hot as i would have expected it to be. What was more worrying was the fact that the coolant reservoir was totally full! (it was half full in the morning). I opened it slowly. Usual amount of hissing (i.e. very little) and it opened with no fuss. Then I removed the spill pipe from the thermostat housing and the coolant level in the reservoir returend to its normal position until the spill pipe orifice overflowed. The top hose instantly became much hotter. Did I have the mother of all airlocks?

Anyway, I ran the engine for a few seconds and upon turning it off, I realised that the cooling fan kept spinning. Viscous coupling was shot (just 6 months old and not purchased in a blue box. I'm not a happy chappy). Fished the old viscous coupling out, whipped the fan off, swapped viscous couplings over, took the car for a spin, hammered it as much as evening traffic allowed me to and the temperature sat at 80 degrees with no further bother whatsoever.

I cannot understand what's happening. Do you think that the change in level in the reservoir was attributed to a duff viscous coupling?

[mmgemini]

When did you last change the radiaror ?

[Reiny]

4 years ago.

[mmgemini]

I'd start there. I remember being told that a 300Tdi rad would silt up in three years. I'm running my 300Tdi without any fan at present.

[Reiny]

Thanks Gemini. Removing the rad is a 30 minute jobby. However I have doubts that it is the culprit. My cause for concern isn't the fact that the engine is overheating because it isn't. It's the fact that the reservoir filled up. I have a hunch that it may be a faulty thermostat. I'll change that first. Ambient temperatures here are very high (32 degrees in the shade at 5 p.m. and there wasn't any shade anywhere). Running without a fan might be ok in the UK but certainly not here.

[Maverik]

Faulty thermostate/air lock by the sounds of it - have you played with the coolent system recently where you might have let air into the system?

Mav

[cackshifter]

Might be a daft question but I take it you are running with antifreeze? It's just if not, you might have formed a pocket of steam somewhere - if the gauge read 95 you bet your bippy it was more than that somewhere else, and if the system hadn't pressurised at that time, it would have been close to boiling. Antifreeze delays the onset of that (apart from the other benefits it brings), but by your care of the rest it sounds as if you would use it.

[bushwhacker]

Air lock (bleed with the expansion tank raised).

Thermostat (check it out in a pot of boiling water).

Water pump (I had a water pump impeller come loose on its shaft it went round by not near good enough to keep the engine at the right temperature.

Hope this helps (you've probably done all this already).

[Reiny]

Thanks for yoru replies fellers. My money's on the thermostat. I have changed an average of one a year (usually they tend to stick open) over the past three years or so. Water pump was replaced last February (P-gasket last October). As you can see, the blasted cooling system has kept me busy.

Maverick, yes I did have an issue with the cooling system in March during a short overland trip. The plastic on the thermostat housing broke (thankfully while i was parked and the engine was turned off). when I replaced it the car was parked uphill therefore I couldn't get all the air out of the system. I kept blowing into the reservoir and after dumping about 3 litres of original Land Rover coolant onto the floor (ouch that was expensive) I thougth that I should have purged all the air. Seems like i didn't.

[Michele]

Mine runs at 95°.

Can't say if the new VDO gauge and sender are not set precisely, or what,

but I replaced the tensioner and the water pump already...

[tweetyduck]

I run mine with an X fan and a kenlow and i've been in 40 and 45C ambient and not overheated except on a long climb in Ethiopia. As soon as my needle moves anywhere off straight up i stop and let the fan kick in and cool down.

You could say i run with no fan....until it comes on and thats usually only when i stop. The fan will run with the keys out.

You surely have something wrong. Try removing the thermostat completely for a while. Also if you drain the fluid, filter it through a pair of tights and re-use it so you don;t have to keep spending money on Antifreeze until you know what the problem is. I'd go Thermostat, Airlocks, Rad, Pump and then give up and buy a new car. Run a Rad flush through before you end up removing it to see if its shot. If your water is carp they do fur up like a kettle. It was amazing what came out of mine

[Reiny]

Thanks tweetyduck. Coolant is squeaky clean. I change it annually and flush the system through.

Had a few minutes to spare this afternoon. First of all, after a short run, temperature hovered at around 80 degrees but the top hose was not as hot as I would have liked it to be. Furthermore, the reservoir was about 3/4 full again. Drained a couple of litres of coolant, removed thermostat, plonked it into a cup of boiling water, didn't notice any difference (which part of the thermostat is supposed to open?), refitted, bled the system and returned home (6 mile drive). Temperature gauge sat at 80 and upon inspection when parked, top hose was nice and hot. Therefore I can only blame an airlock or an intermittedly faulty thermostat. Will buy replacement thermostat and replace YET AGAIN tomorrow.

[tweetyduck]

I presume you are aware that not much if any water goes through the rad until the thermostat sends it there when the engine is up to temp. If the engine doesn't get to temp then the therm remains closed and the top rad pipe will be cool. The therm opens at 88c IIRC and so at 80 there wouldn,t be water going into the rad....well not much.

[Reiny]

Yest that's right tweetyduck. What surprises me is how long it takes to reach operating temperatures. I went to buy the necessary spares yesterday. It was only a 5 mile drive but again, ambient temperatures were high. Gauge sat at around 80 most of the way so I presumed that the thermostat would be opening and closing to retain that temperature. However, when I got there, the top hose was still relatively cold. So does that mean that the coolant within the engine never went higher than 88 degrees?

Anyway, I bought a new thermostat and replaced it and everything seems to be back to normal. I did make an observation though. I think I had overfilled the system last time i topped up. I realized this when I syphoned the coolant out of the reservoir using a length of rubber hose, then I removed the bottom hose from the reservoir, inserted the aforementioned rubber hose into the bottom radiator hose and syphoned that out too. Using this system, losses are minimal however, a glassful or so is almost always lost. When I refilled, I still had almost a litre left in the bucket, even after all the air had been purged. So I guess that's where the rise in level was coming from.