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Author Topic: Cooling problem ...  (Read 1054 times)

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Entwood

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Cooling problem ...
« on: 05 May 2008, 22:25:10 »

Small problem slowly developing that I wish to smack on the head soonest  :)

After a longish run, at least 40+ miles with the 'van hitched, so the beast is working a bit harder than normal, I have noticed I've lost about a cupful of coolant - so this weekend I watched like the proverbial. The temperature never goes above 92 and is usually around 85 whilst towing - when "solo" the temp is usually around 80.

This was found on Friday night:

The leak starts about 5 minutes after switching the engine off, and is now traced to the header tank cap presure relieving.. with the header tank completely full of water ... once the system cools the water level drops to normal.

Exactly the same thing happened tonight on return ... but I deliberately started the engine and gave as couple of quick throttle blips ... water level instantly drops to normal, then slowly rises after switch off.

Conclusion  .. localised heating in the system is causing local "boiling" and subsequent vapour expansion causes the level to rise and the pressure to increase enough to "crack" the expansion cap to do its job.

Now, on the passenger side at the top of the radiator appears to be an additional electric pump in the system - it's not mentioned in the haynes book-of-lies at all - is this the one for giving heating with the engine switched off as the handbook says - or something to do with cooling ??

I haven't been able to make it run yet, but will try a direct 12v across it tomorrow in the light - assuming it is working OK .. what "triggers" does it need to operate  ??

Or am I heading in totaly the wrong direction ???


Any ideas gratefully accepted  :)
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Andy B

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Re: Cooling problem ...
« Reply #1 on: 05 May 2008, 22:36:20 »

Your electric pump at the top of the rad is where my preface lift car has its. I'm not sure what tells it to run, but when mine runs, the rad fans run too. I think your thinking in exactly the right direction. ;)
Pre face lift cars don't do the trick of giving heating with the engine off.
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Mike Collins

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Re: Cooling problem ...
« Reply #2 on: 06 May 2008, 08:46:50 »

That pump should run after shutdown, if the temperature is high enough.

When it failed on my old 2.5, localised boiling in the heads dumped coolant overboard. The motor had become wet and corroded to the point of siezure.

It's fairly noisy when running, so external 12V should show if it's working, or measure the resistance across the terminals.
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Kevin Wood

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Re: Cooling problem ...
« Reply #3 on: 06 May 2008, 09:35:58 »

The pump should run when the engine is hot enough to trigger the first stage of cooling fan, when the ignition is switched off. Easy test - run engine until fan is running then turn off. Pump should start up.

Kevin
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TheBoy

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Re: Cooling problem ...
« Reply #4 on: 06 May 2008, 12:16:14 »

Check carefully for the header tank cracking around thread.

Is it overpressurising?  If not, could be simple cap failure...
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Entwood

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Re: Cooling problem ...
« Reply #5 on: 06 May 2008, 13:52:42 »

Okies .. pump motor runs when connected to 12v - fast highpitched "whir" but very quiet..... but no movement of water seen in header tank.

Header tank neck checked for cracks using a magnifying glass - none seen.

System did pressurise .. but, if memory serves me correctly not by very much, and the "leak" from the cap was about 1 drip a second. What pressure does the system run at ?? and at what pressure should the cap relieve ??

Not had a chance to run it 'til the fans come on ... hope to try that later..
« Last Edit: 06 May 2008, 13:53:26 by entwood »
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Marks DTM Calib

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Re: Cooling problem ...
« Reply #6 on: 06 May 2008, 14:00:27 »

Quote
Okies .. pump motor runs when connected to 12v - fast highpitched "whir" but very quiet..... but no movement of water seen in header tank.

Header tank neck checked for cracks using a magnifying glass - none seen.

System did pressurise .. but, if memory serves me correctly not by very much, and the "leak" from the cap was about 1 drip a second. What pressure does the system run at ?? and at what pressure should the cap relieve ??

Not had a chance to run it 'til the fans come on ... hope to try that later..

Its about 15psi......
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