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Hi, I have a rover 820 vitesse turbo, which will overheat on a journey, after being fine for many weeks.
The temp goes to the max and water seems to be coming through under pressure through the small bore pipe on top of the thermostat housing to the top up/expansion tank.
I have changed the thermostat to no avail. Head gasget seems ok, changed about 1 year ago due to usual oil leak!, heater works ok therfore would indicate no nead gasget leak.
It could be a blocked radiator?

Please could you help.
Many Thanks
Jac
 

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It's definitely worth giving the system a thorough flushing to clear out any gunk in the rad, your head gasket may be damaged and allowing water to contaminate the coolant, thus cloging the rad. up with oily residue, or 'mayo'.

You'll probably get better results if you ask in the "Ask The Gurus" section.
 

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mg_zt_t
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Assuming that there are no leaks in the system, next time you use the car and the engine gets well up to or above normal running temperature (minimum five miles even in this heat - ten is better ) do the following.

Leave car for five-ten minutes after switching off.

Then, using stout gloves, very S-L-O-W-L-Y undo ( NOT remove ) the cap on the coolant expansion bottle. As you slowly undo it, in a healthy engine, at some stage you should hear a gentle 'shuuushhh' for a second or so as NORMAL cooling system pressure is released.

Under NO circumstances remove the cap completely during this test - and remember those stout gloves are essential. The coolant will be extremely hot.

Any sign of coolant being expelled at excessive high pressure from around and under the cap as you slowly undo it, best to stop. Excessive pressure is something you don't want to observe - it's a sign of compression gasses escaping into the cooling system passages - from a damaged cylinder head gasket or worse than that, cracked cylinder head or block - and over pressurising the system.

That is a test the DIYer can do and the result should be 95% reliable either way.

In a bad case of damaged gasket or cylinder head, the cooling system can be so highly pressurised above normal that removing the cap completely can be risky ... correction ,... DANGEROUS.... I have seen coolant expelled so violently from excessive pressure that it knocked the bonnet off it's prop ! Nasty.

So, be careful - if you don't fancy doing this yourself, seek advice from someone more experienced in such things.

Either way, report back and we can advise further.

On the other hand, you could simply be losing coolant via some leak - even via that expansion bottle cap - they wear out - and any coolant loss means the engine can't be cooled efficiently.
 
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