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Defender 200tdi overheating after rebuild


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Hi guys, rebuilt my engine after a heavy smoking problem, smoking now gone and running as usual.

Unfortunately, the temp gauge climbs way too fast and gets to the top of the gauge within only two or three miles of flat, straight fen road driving.

It's really strange, I've filled the radiator up and it shows the normal level in the header tank and the thermostat is new and genuine (the second thermostat since the rebuild)

I first tried taking the thermostat out and it stayed at quarter temp on the gauge while driving a few miles but once it was back in it climbed way too fast again. No steam or anything coming from the bonnet.

Whole engine was stripped and rebuilt, head gasket was done properly and head torqued correctly.

Oil level holding normal, water level doesn't really move even after gauge shows overheating. Fan belts are new and it's on a viscous fan at the moment. Water pump is a year old.

Radiator has no visible damage and it's not done any of this overheating before.

What's up with it??

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So to re-cap, it didn't overheat with the thermostate out... I think thats your solution... its pretty well documented that even "new" thermostates can be faulty, and its pretty much just the luck of the draw - even with genuine LR parts. its an age thing, thermostates have a shelf life.

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It's all original defender engine, no disco conversions, thermostats an 88 wax stat and the temp sensor and gauge are all correct.

I have noticed just tonight that when I ran it and stood it again to try diagnose the thing, the engine was hot as usual and the rad was cold. I opened the top bolt on the rad, no steam, cold water.

But when I lightly squeezed the bottom hose, steaming hot bubbling water appears and the rad and pipes begin to warm up, not a lot but warm.

I think the new pump from a year ago that the old owner put on was am aftermarket and it's had it, what do you guys reckon? It seems that the water just hasn't moved from the engine so surely it's a duff pump? It can't be anything more can it??

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Sounds more like an air lock to me.

Is there a correct process for filling one of these engines and did you follow it?

How do you know the water pump even has water in it and it's not just full of air?

But then again, if it didn't overheat with the thermostat out then I agree with Maverick and it's the stat that's your problem.

Test it or replace it and see what happens.

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Have you replaced the temp sender or was the engine or part of the engine out of another car

This happens if you have a disco temp sender on the engine and trying to send info to a Defender dash gauge.

I say check the sender again

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From this one statment I'm really struggling as to how people can derive any other problems other than a duff thermostate....

"I first tried taking the thermostat out and it stayed at quarter temp on the gauge while driving a few miles but once it was back in it climbed way too fast again"

- Simples.....

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Take out the thermostat.... Put in a pot of water.... Heat pot of water.... Does stat open before boiling?

This is not proof that the thermostate is working properly. been there tried myself. even had another thermostate in the pot with it to compare, with a K- type thermocouple measuring the temp.

If you think its an airlock, verious ways, including "cracking" the heater hosed at the heater junctions and the rad plug when its hot (Carefully), I find driving down a lumpy road a few times does the trick, but never really had a problem with air locks.

Temp senders have been known to die of old age also.

To me though you don't have symptoms of an air lock

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This is not proof that the thermostate is working properly. been there tried myself. even had another thermostate in the pot with it to compare, with a K- type thermocouple measuring the temp. If you think its an airlock, verious ways, including "cracking" the heater hosed at the heater junctions and the rad plug when its hot (Carefully), I find driving down a lumpy road a few times does the trick, but never really had a problem with air locks. Temp senders have been known to die of old age also.To me though you don't have symptoms of an air lock

That's what I'm thinking now, I've looked it over more, it's not pressurising in the coolant system like it should. The pipes stay soft and the gauge claims it's overheating in under a mile.

Can this be a seal? Pressure cap, sender faulty, pipes perished?

I think a replacement of the pipes, rad plastic screw top and header tank cap will do something, if not that I can't see what it is as practically everything is new.

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Only time I had an air locked 200tdi the symptoms were different.

Normal / hot reading on gauge, and cold air out of the heater.

(That was a Disco rather than a Defender though.

I would tend to look at the thermostat given that it runs ok without.

Have you checked the "Y" piece on the small bore pipe is clear? That can prevent the head venting properly.

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Another angle is to fit an engine monitor. I use Engine Watchdog (from Aussie) which monitors the engine temperature or whatever you bolt it to. I attach mine under a bolt on the thermostat housing. At least this way you know the engine temperature, even if lose the coolant or it is not moving.

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I fitted a water level alarm and used the RRC gray reservoir cap, when I squeezed the water hoses I got this faint "wheeze" and I couldn't get the system to pressurize - ended up popping the internals out the pressure cap on the reservoir as it appeared a small piece of swarf had lodged in the over pressure relive valve and jammed it open so it was in effect open to atmosphere, cleaned it out and put it back together and it worked fine.

For the hassle you're going through, buy another couple of new thermostat’s (they’re pretty cheap) mark them carefully and try them out in the vehicle, bit of a faff, but if you do it carefully you won’t lose so much water.

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