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Arierep

Member Since: 13 Apr 2013
Location: Portugal
Posts: 258

1995 Defender 90 300 Tdi SW Alpine White

Defender 300tdi temperature issues

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 stoped, as I was just arriving my destination. Next moring 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, when about the 17/20min mark the temp gauge jumped again past the middle, 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?

26th Feb 2014 12:25am

mk1collector

Member Since: 17 Sep 2009
Location: West Yorkshire
Posts: 6769

Have you checked for an airlock in the coolant system?

26th Feb 2014 12:29am

Interlet

Member Since: 10 Oct 2011
Location: Norwich
Posts: 461

1998 Defender 110 300 Tdi HT Alpine White

I've had a few similar issues in the past.

The 300tdi is an awkward one for cooling and temp gauge, mainly because of two things:

1 - The factory fitted temperature gauge, and the factory fitted temp sender in engine are not designed for each other. This was a factory cockup, that got ignored. The factory gauge is a terrible reflection of actual temperature.

2 - The water pump sits higher in the system than the expansion tank, meaning any slight drop in coolant level, and the coolant struggles to get into the pump, and thus it is unable to pump coolant around the engine. The cabin heater is obviously even higher, so careful monitoring of the heater is quite a good way of quickly finding out about cooling system problems.

(That is why I am surprised that you said it seemed hotter in your cabin when it was sitting on the hot side of the temp)

The combination of these two things mean that you can be rapidly loosing coolant, and your gauge will be lying to you, making you think everything is fine (even if it rises slightly) when in fact, the temperature could be getting dangerously high.

Don't panic Mr Mannering.

If the pump stopped, then an air lock is a possibility, so it's worth checking that out.

Also, check the state of all your coolant hoses, and the radiator. Last time mine got a bit hot, the awkward hose going to the pump near a pulley had worn through, in addition to the radiator getting pierced by a stone. I got away with an overheating situation in this instance because I noticed it quickly, (old cabin heater temp test trick) and the gauge started going up.
I've also had it running hot because the radiator was severely blocked up with mud, cleaning it out caused it to sit at "normal temperature".

It is definitely worth investing in a different temp gauge, with a matched sender, because this will give you some early indication, rather than the LR thing that does not move until big problems hit.

I bought s Stack 270 degree gauge from Merlin Motorsport, although plenty of other good ones out there, such as SPA, AEM, or a cheaper option but still vastly more accurate, VDO.

Trying to decipher what the original gauge is going to be very hit and miss. 1998 110 300Tdi White Hard Top

26th Feb 2014 2:00am

Arierep

Member Since: 13 Apr 2013
Location: Portugal
Posts: 258

Thank you,

How can I check for an airlock?

Also, it might be worth to mention that the heater kept working normally under the circunstances I described

26th Feb 2014 8:51am

Arierep

Member Since: 13 Apr 2013
Location: Portugal
Posts: 258

So, no tips on this?

Also, could this be a thermostat problem?

27th Feb 2014 7:37pm

Interlet

Member Since: 10 Oct 2011
Location: Norwich
Posts: 461

To be honest, I've never needed to check for an air lock, so I don't actually know. I suspect it would involve bleeding the system through the radiator though.

The thermostat is a good point, one that I had forgotten about, it is worth replacing it as well, because it is relatively cheap. 1998 110 300Tdi White Hard Top

1st Mar 2014 12:24am

shaggydog

Member Since: 12 Aug 2012
Location: Kent
Posts: 3346

1991 Defender 110 200 Tdi USW Arles Blue

If you do replace your thermostat, check the one that comes out in some hot water to make sure it was faulty.

Also might be worth checking your viscous fan if fitted

1st Mar 2014 12:27am

Arierep

Member Since: 13 Apr 2013
Location: Portugal
Posts: 258

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?

5th Mar 2014 2:26pm

VeeTee

Member Since: 06 Mar 2011
Location: Somewhere
Posts: 1512

The temp gauge is not very accurate and responsive. I suggest you invest in an external temp gauge, then you can monitor the exact temperature and better diagnose what is going on, also you can place the sensor on different places like engine case, or on the hoses before or after thermostat. I bought one one ebay:

link

Bonus: it can switch relays (for electric fans) or alarm sounder. Cheers, Vincent
1959 Polynorm 1/4 Ton Trailer, Olive Drab Green (sold)
1970 M416 Military Trailer (Camping Trailer Conversion), Epsom Green (sold)
1975 Series III 88 V6, Light Green (sadly sold)
1996 Defender 110 CSW 300 Tdi, Epsom Green (sold)
2000 Freelander 1 TD4 3-drs, Silver (sold)
2006 Freelander 1 TD4 5-drs Facelift Automatic, Tonga Green (sold)

MySite

5th Mar 2014 6:08pm

Arierep

Member Since: 13 Apr 2013
Location: Portugal
Posts: 258

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

5th Apr 2014 5:23pm

Lou Sparts

Member Since: 15 Apr 2012
Location: Kent
Posts: 1501

2005 Defender 90 Td5 XS CSW Zambezi Silver

How does your radiator look ? my 300 Tdi radiator lost most of its fins to corrosion ! Never really caused an issue though,but did run a little cooler when replaced. 2005 Td5 90 XS

Steve

5th Apr 2014 6:38pm

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