HGF on my V6

[archermav]

What an interesting morning. I'm sat waiting for the RAC recovery truck to transport both myself and my 2.5 Connie back home. Had an overheating moment this morning En route to work. Appears that the water is coming out under pressure from expansion cap. Limped it to work, topping water up a couple of times. RAC man turned up, Nice chap. Filled the system with nearly 4 litres of water but pressure still building. No sign of mayo but he reckons head gasket. I'm not sure, but either way she is broken.

[STUBIE]

The coolant will be under pressure when at working temp wouldn't it, perhaps the cap is faulty.

Stubs

[RodgerD]

Don't jump top a HG without further tests. It might well be a stuck thermostat. Don't remove the cap when the system is hot as you will get a volcano of hot coolant coming out of the header tank, that is normal.

Right HG, what colour is the oil, if it a light brown milky colour/consistency, that is an indicator that the HG has failed, or it might be a failed oil cooler. Does the coolant look oily, oil as you know floats on water. Has the coolant got a scummy light brown oil substance, known as mayo mixed with the coolant?

To check if your thermostat is opening, make sure the coolant is completely filled, this means you need to remove the bleed screw on the bottom hose. If you look down next to the air cleaner and under the air trunking leading to the throttle body, you will see a hose with a bleed screw, remove the bleed screw, top up the coolant until coolant flows freely. Replace the bleed screw and finish topping up the header tank. Once you have done that and starting from cold, run the engine, feeling the top hose that runs to the radiator and the bottom hose (the one with the bleed screw). The top hose should get progressively hot, whilst the bottom hose should remain cold. It the thermostat is working, all of a sudden the bottom hose should get hot, which means that coolant can flow through the thermostat. If the bottom hose doesn't get hot and the top hose is hot, then the thermostat is stuck shut.

You also need to check the fan is working. Running the engine and push the demist button on the A/C panel, the fan should be running, if not you have a fan issue that needs sorting.

BTW if the top hose gets hot, then you haven't got an air lock in that part of the system and the engine should remain within it's operating temperature, this being irrespective if the heaters get hot or not. To check there's no air in the heater circuit, just feel both hoses, to/from the heaters, they should both get hot at the same rate as they aren't part of the circuit controlled by the thermostat.

My bet either a thermostat stuck closed , or if she boiled in traffic, a kuput fan.

[SD1too]

Originally Posted by archermav

RAC man turned up, Nice chap .. he reckons head gasket.

All breakdown men say that Simon, not only about Rovers but a colleague's VW Golf as well. It's usually a random guess so not worth losing sleep over. The KV6 engine is not susceptible to unprovoked head gasket failure. You've done the right thing coming to us.

Stubie and particularly RodgerD have given you excellent and comprehensive advice of how to proceed with some simple tests to determine what is wrong. I urge you to take heed, and let us know the results.

Simon

[DMGRS]

First suspects, based on experience:
Expansion Tank Cap
Thermostat Assembly
(both clickable, if you need parts)

We had an almost identical situation on a friend's 75, random boiling over and overheating. Turned out to be a very knackered thermostat.

Good luck!

[archermav]

Thanks for the replys gents, just got home.

Stubie, a couple of months back I replaced the expansion cap, after a similar episode that I wrote off as a knackered cap. Bought one from DGMRS.

Last week I noticed coolant lying ontop of the expansion tank, as if it had come out via the cap, so only yesterday ordered another, just in case.

RodgerD, oil seems fine, normal colour and nothing dodgy re mayo, at least to these untrained eyes. When the RAC man was trying to fix it,he did indeed remove the bleed screw whilst topping up the system. He then stated that the bottom hose wasn't getting hot, whilst top hose was warming nicely. He took this as a sign of HG failure.

I'm fairly sure the fan is fine, I pressed the windscreen button and the air blew nicely.

I also recall sitting in traffic this morning listening to the fan, which I don't normally notice.

Stuck thermostat then ? Thanks again for the response.

[RodgerD]

Originally Posted by archermav

Thanks for the replys gents, just got home.

Stubie, a couple of months back I replaced the expansion cap, after a similar episode that I wrote off as a knackered cap. Bought one from DGMRS.

Last week I noticed coolant lying ontop of the expansion tank, as if it had come out via the cap, so only yesterday ordered another, just in case.

RodgerD, oil seems fine, normal colour and nothing dodgy re mayo, at least to these untrained eyes. When the RAC man was trying to fix it,he did indeed remove the bleed screw whilst topping up the system. He then stated that the bottom hose wasn't getting hot, whilst top hose was warming nicely. He took this as a sign of HG failure.

I'm fairly sure the fan is fine, I pressed the windscreen button and the air blew nicely.

I also recall sitting in traffic this morning listening to the fan, which I don't normally notice.

Stuck thermostat then ? Thanks again for the response.

Mr RAC man want's sacking, if bottom hose isn't getting hot and top hose is, that isn't a sign of HGF, it's a clear sign of a stuck thermostat. But then it's a Rover, so it must be a HGF, even though on a v6 is not that common.

Repeat the top/ bottom hose test again, if the bottom hose doesn't get hot, then whip out the thermostat and treat the car to a nice new one.

[Ps3000]

Welcome to my world (sort of). Mine's not overheating, but it is forcing coolant out of the cap. Since Feb I've replaced the Rad, put new stainless pipes on the front, replaced the inlet manifold gaskets and thermostat, replaced the fan resistor and I've replaced the cap (and tried the old one back on), bled the system countless times, all to no avail.

I'll be interested to hear what this turns out to be.

I've been to get a "spare" engine today

[archermav]

Rodger, will do, CheeeRS

[RodgerD]

Originally Posted by Ps3000

Welcome to my world (sort of). Mine's not overheating, but it is forcing coolant out of the cap. Since Feb I've replaced the Rad, put new stainless pipes on the front, replaced the inlet manifold gaskets and thermostat, replaced the fan resistor and I've replaced the cap (and tried the old one back on), bled the system countless times, all to no avail.

I'll be interested to hear what this turns out to be.

I've been to get a "spare" engine today

Have you done a compression test and a coolant hydrocarbon test? Cheaper and easier than replacing the lump.