Defender Tdi300 cooling system

well, a warmer day today, good test, the motor was well up to operating temp before the climb. I didn't see the replies below about blocking off heater so thanks but I blocked off one of the hoses anyway.


It was a good test, no gear changes with traffic. The temp didnt move for a until a lot further up the hill this time so I think that does contribute to some of the temp increase but it did eventually get up to 3/4s. Interesting experiment but I will keep looking for other clues. Thanks to your advice, I will keep the heater unblocked after all, it's another means of cooling coolant when it gets warm despite, the discomfort. All other hoses appear to be free flowing but will check when I descale and reverse flush. cheers

I recently had similar issues but turned out to be the vdo gauge had failed.
My gauge would be accurate up to about 92 then would punch over to 100+ rather quickly.
To ensure the cooling system was ok, I wound the spring on the thermostat down onto the bypass plunger forcing the thermostat to be open.
This gave me a running temp of about 77 degrees.
This proved to me that the head was not cracked and there was no actual overheating problem.(spring mod was for testing only)


My engine takes 7kms @60/70kph to reach operating temp. Thermostat opening can be seen as a spike on my gauge.
I boiled up 4 brand new waxstat thermostats to check the opening temps.
They varied from 88 to 95 and the amount they opened was just as varied.
I used the earliest opening thermostat which was fully open @ 88.

Installed a VDO mechanical gauge and now I have an engine temp of 87 to 94 with an average of 89 on the highway.
If I let it idle, the temp will drop down to 84.

I hope this might help.

I've installed a VDO electrical sender and gauge to replace the original, as well as a TM4 with the sensor bolted to the back of the head, to monitor head temps on a 300Tdi 110SW

The coolant runs 10-20.C hotter than the head. Occasionally the TM4 (set to 100.C) will alarm on a hot day on a long high speed hill climb. The VDO reads up to 120.C for those short bursts, but since I hate the screech of the TM4, it doesn't take long for me to back off and turn the heater on, to drop the temps back down. Operating temps are between 85.C and 95.C on the coolant (cooler on the head) for high speed, warm day driving.

I've fitted a larger intercooler and VNT too. After fitting a vent to my LHS panel to allow increased air flow through the radiator and intercooler, and to wash off exhaust heat from the firewall, I found EGTs dropped by about 50.C. I suspect the mod also helped with radiator cooling, but I don't have any figures. I cut a big hole saw hole in the side, and covered it with one of the heater vent scoops, facing backward. That way if I ever need to retain air pressure under the bonnet, say to maintain a bow wave, I can just duct tape over the vent opening.

Another temp to gauge (for those with overheating paranoia) is the gearbox. On a drive from Melbourne to Sydney, on a warm (low 20's) day, the gearbox didn't get to 70.C despite 110kph and some high speed climbs. But 30min out of Port Augusta on a hot day 35.C+ the gearbox was over 95.C! I kept my speed down on that trip, but have since fitted an oil cooler to the R380, which also drastically reduces seat box temps.

Having actual temp readings has sure increased my mechanical sympathy.

Another vote for a mechanical temp gauge......ditch the OEM gauge

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Originally Posted by Michael2

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The coolant runs 10-20.C hotter than the head. ....

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I found that the temperature of the head can vary by about 10 degrees itself, depending on where you measure from.

Front of head at the thermostat cover I get the same reading as the coolant gauge(thirdparty gauge, not car gauge).
the D1 Tdi consistently runs at about 83C without fail(whether it's 15C out or as recently 30+C out).
Because I'm a bit of a geek, I occasionally get curious as to the temps of various parts.
So the Al housing of the thermostat reads as per the guage.
Just behind it and to the left as I get closer to the exhaust it gets hotter.
Middle of head between the injectors I've seen 91(where coolant was still at 83C and car idling)
towards the back of the head on the drivers side it was back down to 80-ish(81-84). Passengers side middle and rear corner were more like 90-ish again.
Rocker cover with noise mat off measured high 70's.
It generally depends on the time of day and how long the bonnet has been open for(longer bonnet up = cooler by a couple of degrees).

This issue of getting hot air out of the engine bay an interesting one. I guess the design of the engine bay hasn't changed since the series one. I had a stripped series one one as a cubby when I was a 5yr old, the redbacks didnt mind sharing their home with me, I use to enter the engine bay though the gearbox tunnel. It was tight even for a toddler so filling this hole with a gearbox and motor is very snug. I wonder as a test, has anyone taken a defender that is prone to getting warm up a hill with the bonnet off?? It seems ironic that one small vent can make all the difference. I wonder how they go in Africa with hot days.

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Originally Posted by swivelrat

.... I wonder as a test, has anyone taken a defender that is prone to getting warm up a hill with the bonnet off?? It seems ironic that one small vent can make all the difference. I wonder how they go in Africa with hot days.

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Not exactly, but close:
about 20 years ago I had a 79 RRC. low(8.13) compression, and I used to run very high advance via a Bosch dizzy.
Car ran fine in all weather, never overheated, 48C on trips to Lake Eyre and so on.
On one trip to Ayres Rock(as it was called back then) it started overheating just out of the blue, no warning.
needle in the red zone. Of course I pulled over to check stuff.
Not a lot of pressure in the system, but I still let it cool a little, check water, etc, etc.(I'm in Melbourne, so a long way to drive with it overheating!)
I was coming back from The Olgas and had to stop to check it all again.
Had a slightly higher temp(92C) thermostat in the spares box, and the one in the engine was an 88C.
My thinking was that maybe the thermostat was stuck closed.
Couldn't test it, so just swapped it out and tried to keep heading home.
Still running hot and the ambient was about 30C or so.
Below about 80km/h, I could keep the temp needle just below the redline .. I suppose it made me feel safe. :D
But with all this overheating the engine never actually felt overly hot.
ie. loss of coolant, nor excessive pressure in the hoses(I could easily squeeze them).
I didn't want to drive home(2400klms at less than 80k/hr) and at another wayside stop, and now it's dark, I found an open box(like the ones that fruit comes in with an open top part) and wedged in under the bonnet.
Wired the bonnet down so it wouldn't flip up and drove with the bonnet half up. I'd say about 3 or so inches of air gap between bonnet and grille tip.
Needle immediately dropped and barely moved off a quarter now with so much air coming through under the bonnet.
Luckily for me I never got pulled over by cops in those 2400klms for 'unsafe driving' :confused: .. but I got home.

Spent many $ wasted on a few wild guesses as to what the issue was, and myself nor mechanics could find anything wrong with it.
The only things I didn't change were radiator(flushed many times) and the temp gauge.
Changed water pump, hoses, etc and so on, all to no avail.
Flushed engine, and radiator a few times over the course of the next two years again all to no avail, and just drove the car with the temp needle on the red line.
Again, the engine never felt excessively hot, other than the reading on the needle.
One day (2 years or so later) I accidentally brushed my hand against the outside of the radiator fins and they crumbled into dust.
Radiator was removed twice early on in the diagnostic period for flushing too tho(once by me and once by a radiator place)!
No one ever thought just to replace it .. and why would we when it seemed fine.
Anyhow, after two years and now obviously looking shot, a new one was bought.
Immediately the temp needle settled back to it's normal middle position! :D
Then the thought occurred to me that I drove it overheating .. actually overheating, for two years and about 100k klms :p

air gap between bonnet and grille = more air = cooler engine than it otherwise may operate for those conditions.

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Originally Posted by swivelrat

I wonder as a test, has anyone taken a defender that is prone to getting warm up a hill with the bonnet off??

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One hot summer day we were playing in an ex-army SIIa GS on some offroad tracks. They were a combination of steep hills and sand dunes. The engine was getting quite hot and starting to vent excess pressure. We took the bonnet off and kept playing. The engine temperature came back down to an acceptable level.

Aaron