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Old 8th November 2020, 14:49   #1
Phil-Hex
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Default Cdti overheating

Hi folks
Bit of an unusual one, my cdti is overheating!
I've replaced the top hose stat with a tested one.
Hot water didn't appear to moving through the rad, so took bottom hose off to backflush it, water came out the rad but nothing from the engine side?
Rad is running freely
With bottom hose off header tank is still full of water
Run engine with bottom hose still disconnected and got a good flow of water out of bleed point... Suggests water pump is still working well?

At a loss now as I know the rad is now empty but the header tank hadn't drained and still no water coming out the engine at the bottom metal pipe?

Temps are getting well above 115degrees, fan is coming on at 100 but there's no flow through the rad even though there's no restrictions so no CD water reentering the engine

How much is a Ztt worth as scrap?
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Old 8th November 2020, 15:24   #2
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You have replaced the top hose stat....

They have been known to cause a problem at times, anyway it will be closed when cold. Remove it completely and then check everything.
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Old 8th November 2020, 15:34   #3
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As above remove top and bottom hose from the engine the flush water through the engine, you have a restriction somewhere. Original stats usually fail open but it's possible your issue is with that or a collapsed hose somewhere in the cooling system.
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Old 8th November 2020, 15:37   #4
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Problem started before I replaced the stat hence the replacement,( previous one was working fine for 100k and obviously still was as a new one hasn't solved the problem) it was tested in boiling pan and working 100%
Just run car up to temp, its opened and allowed the coolant I drained to be replaced back into the system but now is overheating again if revved up.
It's as if the water will not go out of rad back into the engine yet it runs out of rad freely if the pipes removed?
Is there anyway the engine can airlock?
At 276k, mot looming and NAUGHTY WORD-NAUGHTY WORD-NAUGHTY WORD-NAUGHTY WORD- bodywork I'm rapidly losing the love with it
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Old 8th November 2020, 15:40   #5
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Original stats as in the factory fitted one not your other top hose stat. The diesels usually bleed themselves but it's worth giving it a go just to eliminate that as the problem. I would flush the engine with both hoses removed first though.
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Old 8th November 2020, 15:51   #6
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Quote:
Originally Posted by Phil-Hex View Post
It's as if the water will not go out of rad back into the engine, yet it runs out of rad freely if the pipes removed
The coolant path from the radiator ends at the original thermostat which is clearly not opening at all. If the wax capsule has lost any wax, it won't open the valve and the engine will overheat. A fully operational inline stat won't prevent that happening. Inline stats only work if the standard one opens, typically at too low a temperature for normal runnung.


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Old 8th November 2020, 16:32   #7
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So the original stat can change its position after being in the failed position for at least 5 year?
Car ran very cold when I got it hence the first hose stat, wil pull the original out and see if that helps
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Old 8th November 2020, 19:51   #8
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Originally Posted by Phil-Hex View Post
So the original stat can change its position after being in the failed position for at least 5 year?
There isn't a 'failed position'. It's either shut or open according to coolant temperature, but will remain shut if the wax capsule fails completely. This would explain your observations about coolant flow/drainage. I can't think of a more likely one.


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Car ran very cold when I got it, hence the first hose stat. Will pull the original out and see if that helps
The original stat was obviously opening early as they generally do, but if the inline stat is fully operational, then clearly something is now preventing coolant flow through the head. Testing the original is the only way to know. Having done that, replacing it with the current, so-called Mk3 version, will probably negate the benefit of the inline stat.



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Old 9th November 2020, 01:24   #9
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hi to all
when the engine is hot put your hand on the top hose and see if there is hot water coming through also feel the heater pipes to see if they heat up i had this trouble and it was a air lock which took some time to clear also is the cooling fan coming on at that temp it should come on if you know some one with a t4 they can test the cooling fan what i would do is drain the system and refill then with the engine running and the rad cap on wait for the engine to start to warm up then open the bleed screw and see how much air comes out if tap water has been used it could have caused a blockage you should all ways use de ironized or disstilled water
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Old 9th November 2020, 07:16   #10
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Quote:
Originally Posted by Phil-Hex View Post
Is there anyway the engine can airlock?
At 276k, mot looming and NAUGHTY WORD-NAUGHTY WORD-NAUGHTY WORD-NAUGHTY WORD- bodywork I'm rapidly losing the love with it

Yes if the small pipe that enters the top of the expansion tank gets blocked it will. Run the engine at idle with the cap off and make sure coolant flows into the expansion tank.
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