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Interlet

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

1998 Defender 110 300 Tdi HT Alpine White

Hot running but not fully overheating

I've got a puzzling issue with my cooling system. I flushed the coolant the other day, although the rad didn't really get treated.

I have a Stack 270 degree gauge with matching sender.

In the past 8 months the coolant would get up to 95 initially then come back down to normal temp about 88-92. As I understand it, this is the designed range, and stat is meant to open at about 88.

When I did a flush, I bled it and fitted a new stat.

Now, it all works even hotter...gets to about 98 before going down to 94ish.

The heater blows perfectly hot air and the engine is otherwise running fine.

The radiator is only about 18 months old if that.

Apart from one physically noticeable thing I would speculate the issue is electrical, but the radiator does not give off any heat, and the top pipe to it is luke warm at best, while all other hoses are very hot.

But the engine has no other noticeable issues....I drove from Norwich to Huntingdon this afternoon with the temp just bouncing between 93-96. 1998 110 300Tdi White Hard Top

23rd Feb 2018 7:47pm

Puffin

Member Since: 13 May 2017
Location: Cardiff
Posts: 30

1988 Defender 90 V8 Petrol CSW Alpine White

If your top hose is only luke warm and your temp gauge is stating 90's then your thermostat is not doing a job or you have an air lock? high 90's is very hot

You shouldn't be able to put your hand on your top hose for too long..

Puffin

25th Feb 2018 8:52pm

TimS

Member Since: 06 Jul 2015
Location: Northants
Posts: 20

You have air in the system.

The header tank on a 300tdi is too low, so try unmounting it and raising it up on blocks, squeeze all the pipes through in the direction of flow and then remove the thermostat and radiator fill ports and top up. Take it up to temp squeezing the hoses through.

If this doesnt work, you may have a faulty air bleed on the thermostat. Worth popping out and checking the little bearing is moving as it should and it at the top. Easy to put in upside down and then it wont bleed the air back to the tank.

Could also be the Y-connector on the rad bleed or a faulty cap on the header tank.

Check all these and repeat the process.

You could also loosely disconnect the heater pipes while the engine is running to force out any air that my be trapped. These are the same/higher than the header tank so a common place for air to get trapped.

Tim

27th Feb 2018 11:13am

Mo Murphy

Member Since: 01 Jun 2008
Location: Letchworth Garden City, Herts
Posts: 2078

1984 Defender 90 200 Tdi HT Pennine Grey

Try putting the old thermostat back in.
I had a similar problem with a replacement Waxstat and a genuine item. The 88° Waxstat kept the engine at a steady 96° and the genuine I bought to replace the defective Waxstat (exactly the same and made by Waxstat but in an LR box) kept it at 98°-100°.
I put the original thermostat back in (genuine 7 years old) and normal service was resumed.
HTH
Mo The Land Rover 90 - Many are called, few are chosen.

27th Feb 2018 11:32am

TimS

Member Since: 06 Jul 2015
Location: Northants
Posts: 20

Mine runs at a constant 86-88 with an ally rad.

27th Feb 2018 3:45pm

TimS

Member Since: 06 Jul 2015
Location: Northants
Posts: 20

The standard temp gauge on a 300tdi is rubbish. Dont go by the temps as they are wildly inaccurate. Use a dedicated gauge or MadMan if you can.

Tim

27th Feb 2018 3:46pm

Interlet

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

I've tried bleeding it everywhere, including the heater pipes, and I'm struggling to see where any remaining air could be.

TimS, read original post, I don't have the standard gauge.

During today's arctic temperatures, I gave it a blast and it was a bit cooler, peaking at 94, but when I come off the dual carriageway and onto roundabouts and traffic lights, the temp got down to 80 by the time I rolled back to my house.

Only other thing I can think is the seal and the U-bend pipe at the thermostat. That was a pig to seat properly, although the alignment was correct. I might look at that next.

My previous stat still got too high, but it did come down to 90ish...I might put that back in. 1998 110 300Tdi White Hard Top

27th Feb 2018 11:39pm

TimS

Member Since: 06 Jul 2015
Location: Northants
Posts: 20

You can check the stat opening temp using some hot water and a thermometer in a pan. Useful for your own peace of mind that the stat is fully opening at the correct temperature.

27th Feb 2018 11:42pm

Interlet

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

Ahh, good point, we actually tested both at the same time before we fitted the new one. Both work fine, and open roughly the same time as each other. 1998 110 300Tdi White Hard Top

27th Feb 2018 11:57pm

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