3.9 overheating

I'm confused about hot water gushing out the tank - this happens when you take the cap off a hot engine because only the pressure stops it boiling. Once you take the pressure away it boils violently out of the top. If it is suddenly doing this without the cap ever being on then ISTM it has to be air pressure from the compression cycle.

If air is suddenly rushing through would that perhaps indicate that the head gasket is only blowing once a certain temp has been reached?

Might be worth a compression test - hot and cold?

HTH

stab in the dark here, but could it have gushed in such a manner having been waiting for the thermostat to open thus allowing pressure from a head gasket failure/failing to over-pressurise the rest of the system and thus gush from the open expansion tank?

overly hot pipes would make me think about the radiator not doing it's job (much damage/blockage) or the water pump failing to move the water through the radiator?

Just throwing ideas in, I know bugger-all about V8's.

Regards. Mark.

Sounds like the dreaded liner problem, I'm afraid, but has to be worth replacing the thermostat first. Fit an 82 degree one, not the std 88. Badger.

did it only boil when you took the cap off? if so, what Tim says is correct. Are you losing water at all, I dont mean a leak but are you having to top it up? I thought my V8 90 was over heating and it turned out to be the temp transmitter. Richard

It is doing it without the cap on.

If it is the head gasket, what sort of results could I expect? Would I have to change the gasket on both heads, assuming that the results indicated which head was at fault?

Bit of a novice on V8s..sorry!

Paul

Those are the symptoms....the water just sits there, then all of a sudden, it appears as if something has just opened to let a load of water through.

I flushed the radiator, but I didnt take it out and do a reverse flush...

You probably know more than me!!!!!!

Paul

When I stop the engine, there is a hissing coming from the expansion tank cap...even though its on tight....I've never owned a V8 before, but even with my limited knowledge it doesnt sound normal....

Paul

i got the same thing with my V8 landy today, but i think the reason for me was a bit more simple! a dirrty radioator, and a VERY dirty engine. !

If the rad has been flushed then that discounts that possibility, also water pump not pumping the water around mebbe? I don't know if the water pumps on V8's are a similar affair to the diesels I'm more familiar with.

Can you whip the thermostat out and run it without for test? my thoughts being that if the cooling system is being overpressurised then the opening thermostat could be allowing this pressure through to the expansion tank, by removing the thermostat temporarily this pressure will be evident much sooner and hopefully less dramatically.

Maybe an academic excercise as a head gasket blowing into the water jacket sounds likely to me, though I'm not sure how the symptoms compare to those of the slippy-liners, I spose a new block would be the route if that were the case.

I'm paying close attention here as I hope to soon be buying a 3.9 disco.

Regards. Mark.

Someone else mentioned water pump...apparently fins get corroded and dont pump efficiently.

Again, this was mentioned. I've replaced the thermostat, but to be honest I havent been on a long run since changing it. I'm going to run it for a few days, keep my eye on the coolant level (checking when cold) to see if water is being lost anywhere.

What are slippy liners? And where's the water jacket?

Thanks, Paul

Had this on an Espace. Tom also had this on his 101. In Both our cases it was a leaking expansion cap. Allows the pressure to escape and thus the water to boil hence overheating.

My hit list would be

HTH

Lee D

The block of a rover V8 is made from cast aluminium, the cylinders are lined with steel jackets (kinda like steel tubes), the 3.9 range rover is prone these steel liners slipping within the bores due to overheating due to a different fuelling map in the ecu causing hotter running (the same engine in the discovery had different fuel mapping in the ecu and doesn't have this problem.

The water jacket (am I useing the correct terminoligy here chaps?) is the routes and channels within the engine block through which coolant flows, there are also channels carrying oil, which is why when a head gasket fails the pressure in the pistons can push through into the coolant, a head gasket failure can also mix coolant and oil, pressurise the oil, blow out the side of the block etc depending on how and where the gasket failed. These routes and channels flow from within the engine block into the cylinder head and the head gasket seals this join.

Regards. Mark.

PS, mebbe some info here

Regards. Mark.

On or around Sun, 19 Jun 2005 13:24:30 +0100, "Pacman" enlightened us thusly:

Does it have aircon?

Sister's BF had many hassles with an overheating 3.9, and I suspect they were never really resolved until he removed the aircon rad. I suspect that is incompatible with wokring aircon, though.

when it's hot you often get that hot waterfall effect, IME.

On or around Sun, 19 Jun 2005 15:11:16 +0100, MVP enlightened us thusly:

it gushes thusly because you've depressurised and made it boil almost instantly.

water at 15 psi overpressure doesn't boil if more than 100°C, as soon as you depressurise it, this water at 100+ flashes to steam, or some of it does.

It's not, by itself, sypmtomatic, except in as much as it shows you that the system does indeed pressurise as it should.

Overhaeting likely to be down to poor airflow, partly blocked rad, and hot weather, in one or another combination.

On or around Sun, 19 Jun 2005 19:32:20 +0100, MVP enlightened us thusly:

IME, it's next-to-impossible effectively to flush a partly-blocked rad. The amount of water you can introduce from any normal sort of supply will be acrried easily by about 10% of the radiator tubes, so a half-blocked rad won't clear by flushing it.

Fill with a solution of caustic soda, wait an hour or so, then re-flush. Just make sure you get it all flushed out before refitting, ally engine bits don't take too kindly to caustic soda, even a mild dose! Badger.

I think the cause is a blocked rad, as the top pipe is a lot hotter than the bottom pipe, so it looks like it will have to come off. Will shoving my jet washer in it clear it more effectively??

Paul

Doesn't that actually prove the opposite?

Is the radiator an even temperature or are there hot / cold spots?