Bleeding coolant system

200tdi Disco in a defender.

I am having a few problems coming to the end of my rebuild. I have spent 2 days trying to get the coolant sorted. Filled it yesterday and ran it and it got to 95 degrees and there was no drop in the temp gauge (Durite capillary gauge). It used to drop perfect at 88 degrees before I did the chassis swap.

Took the thermostat (Waxstat 88 degree) out and tested it in a pan of water, opens perfect at 88 degrees as it should.

Decided to drop the water pump off to check that was all ok and it is still all perfect.

Put it all back together again and still having the same problem, get up to 95 degrees so I shut it off again

Below is the method I have used to bleed the system of air.

Set heater control to max heat
Remove expansion tank cap
Fill rad through top plug
Wait for coolant to move through system
Top up through rad top plug as required
Replace rad plug and expansion tank cap

Radiator hot top to bottom, all hoses hot, heater working amazingly.

Any ideas what is going wrong?

200's are not usually hard to bleed and it sounds like you have done all the right things and the system is working as it should. The only thing I can think is to check engine temp with an IR reader. Is there a chance gauge capillary has been damaged ?

It's the stat opening?

tottot said:

The only thing I can think is to check engine temp with an IR reader. Is there a chance gauge capillary has been damaged ?

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Not thought about gauge being a problem, will give it a try tomorrow with an IR temp gauge.

kermit_rr said:

It's the stat opening?

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Stat has been tested and is opening spot on at 88 degrees, or so the wife’s kitchen thermometer tells me

Ok mines a petrol, but starts to open at 82c and pretty sure it's fully open at 96c
Have you checked the flow through the radiator? Can you feel it get warm part way down as the stat opens? IR thermometer is good for this

kermit_rr said:

Have you checked the flow through the radiator? Can you feel it get warm part way down as the stat opens? IR thermometer is good for this

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The radiator is hot from top to bottom and all the hoses are hot as well, so water is flowing as it should.

If it's hot from top to bottom then is it doing its job? It should be dumping heat and getting cooler as it flows through

Is the fan...er... fanning?

kermit_rr said:

Is the fan...er... fanning?

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Yes it is turning round and round

I might be imagining this, but have I read somewhere that there's compatibility issue between a Disco sender and a Defender gauge

Al2O3 said:

I might be imagining this, but have I read somewhere that there's compatibility issue between a Disco sender and a Defender gauge

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I am using a Durite capillary gauge and sender so there shouldn’t be an issue here.

If the water pump, radiator and stat are all working then I'm at a loss. Like i said, i don't know you're engine, but I'd be tempted to let it get a bit hotter. Someone may come along and contradict me but i would expect a normal engine regardless petrol or diesel should be ok to 100c with no issue, assuming the pressure cap is holding pressure ok. It might just sort itself out

It does sound odd, but the rad should be much cooler at the bottom than the top. I'd take the thermostat out and run it to see if the overheating is still happening. I found that their operation in a pan of water is different than when installed.

I would second the above, run it without a stat and see if it still gets up to the high temperature. if it does it points to either the rad not working properly, or more likely form your description the gauge/sender not working properly.

ivancrx said:

Yes it is turning round and round

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this may be with checking a little more thoroughly. If it is still the original viscous fan these can fail open. they still spin but are not locked, a very crude test to be undertaken carefully is once up to temperature turn the engine off and immediately see if the fan rotates separately from the centre hub, a more dangerous test is to try and stop the fan spinning with a piece of wood while the engine is running. With ether of these test on a hot engine you should be able to establish if the fan has locked up with the heat or not. Friend had this happen in Morocco and blew the o-rings on his td5 water pump. Even with an overheating engine and a furiously spinning fan if you held something against the fan blades it would stop and the hub alone would spin.

I ran my 200tdi Defender in the UK with no viscous fan for 4 years no issues (as have others) so doubt the fan is an issue. As stated I would check the gauge is accurate before anything else but also as stated the rad should be cooler at the bottom than the top if you have correct coolant flow. Did you flush your rad out as part of your rebuild?

Interceptorxj said:

Did you flush your rad out as part of your rebuild?

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Rad has been flushed through yes, it has only done 500 miles. My next lan is to remove the stat and see what happens
Many thanks for all the suggestions I have a way forward for now.

Question.

Have you fitted a stat that doesn’t have the joggle/bleed valve in it?

flat said:

Question.

Have you fitted a stat that doesn’t have the joggle/bleed valve in it?

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No it has one in and it is free to move.

ivancrx said:

No it has one in and it is free to move.

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okay good, not sure what else then
Only other thing to try is fill it up via the radiator then when that fill, put the lid on then fill it up via the expansion tank, agitate all the pipes etc as best you can as you do it, and when its running then take it for a drive to get it hot.
I wonder if there is some sludge somewhere clogging it up, has the rad been back flushed etc?