Cooling problems and pressurising

Hi

As an additional problem to my gearbox (see another thread), my cooling system has started to play up. I have a 91 RR with a 3.9Efi. It sounds ok, it starts every time no problems. However I have no hot air from the heater, and can hear hissing from the expansion cap after the engine has been reved. The top hose also goes rock hard.

I know what everyone is going to say it is the head gasket, but I am not convinced!

Now for the strange bit. If the engine is left to idle, the top hose doesn't harden, and neither does the expansion tank hiss....okay still no hot air from heater, but that could be a seperate problem. The radiator at idle gets nice and warm all over. If you test for exhaust gases in the coolant the test comes back negative.

But the strange thing is that the second it is reved it all gets pressurised. Any ideas, as my friendly new mechanic is scratching his head and we are having a debate between head gasket, or is it possible that when the engine revs are raised, the water flow increases round the system and something is obstructing it...eg radiator partially blocked and when reved gets blocked, lets say by a baffle or something, and once the pressure is there the blockage is held in place and hence doesn't quickly go away.

I know this is a long shot but worth asking the experts.

Any help would be great

Many thanks

Matt
P.S.
Anyone know where to get a new seal for a metal sunroof without paying the earth at a Landrover dealer?

Hi,

Have you got a sticking thermostat? It might be worth checking this first for what it costs.

B.

hi there, yes definately try the thermostat by testing it in cold water and slowly adding hot water to raise the temperature and the thermostat opens up inside,if all ok then radiator(waterways) need flushing.Had same problem on
rover 800 vitesse,same symptons,sent it to Rover,they said it was a fuse,got
it back,blew the head,sent it back to rover(couldnt get it in anywhere else so
soon)cost nearly £2,000,got it back,same symptons,had a close look with a good friend,NEW RADIATOR £112 BINGO!got peed off,gave car away.