The V8 Owners Forum -

Got a funny which is defeating me.

Drive the car around town etc or at modest speeds and it seems never to need topping up, coolant wise.

Drive it fast, and it appears to push some coolant out of the header tank, past the filler cap. A bottle on the overflow confirms this. And the low coolant light comes on. There are sensors in the rad and header tank. Driving along at speed the light will go on and off at will. But when cooled down, a visual check shows the coolant below the sensor level in the header tank, but never in the rad. Almost like it's finding its own level.

A pressure check hot or cold shows no leaks. I've replaced the filler cap a couple of times, and the seat looks just fine. What I haven't yet done is do a pressure check which includes the filler cap.

Heads were planed to take composite gaskets. Outer row of bolts omitted.

Are you using the Viscous fan? MuscleManta (who is also on the SD1 forumn as someone or other) had no end of trouble with coolant issues, the engine temp of his 4.6 would be all over the place, in the end we removed the fan and went electric....problem solved. I think something had gone wrong with the standard fan, it never really free-wheeled, it was always spinning at a reate of knots!

Sounds like a very minor leak between combustion area and water jacket to me.

Chris.

Do you have a single or double seal radiator / pressure cap?

Single pumps coolant out as it heats and there it stays
Double pumps it out as it heats and then draws it back when it cools

Ian

Ian Anderson wrote:Do you have a single or double seal radiator / pressure cap?

Single pumps coolant out as it heats and there it stays
Double pumps it out as it heats and then draws it back when it cools

Ian

The SDI has a separate header tank. The pressure cap is the correct one - as far as I know. Bought from Rimmer. Another from Ebay. And the old one. All seem to do the same.

If I rig up a bottle to the overflow pipe from the header tank, it fills with water. Pretty well what is lost from the header tank. But only when pressing on - it stays empty when driving more gently.

sidecar wrote:Are you using the Viscous fan? MuscleManta (who is also on the SD1 forumn as someone or other) had no end of trouble with coolant issues, the engine temp of his 4.6 would be all over the place, in the end we removed the fan and went electric....problem solved. I think something had gone wrong with the standard fan, it never really free-wheeled, it was always spinning at a reate of knots!

Mine is a (near) standard engine, still 3.5. Has the standard temperature controlled viscous as fitted to the injection models.

But the problems seem to happen when driving quite fast - so the fan really won't come into the equation.

The temperature on the gauge does go up and down a bit seemingly at random, even at a steady 70 or so MPH. Between about 90-100 on the gauge.

It's probably worth having a sniffer test done on the coolant.
I hope ChrisJC's comment is not the problem.

FYI, my SD1 book says that the thermostat is an 82 Degree type and the expansion bottle cap is a 15 lb/in2 type.

Regards Denis

Later SD1 have 88C thermostat. That's what I've got fitted.

Can't see it being a head problem. Changed the heads fairly recently for Stage 1 units planed down for composite. Both heads and block were fine on my straight edge and looked perfect. Plugs show no sign of water getting to them, nor does the oil.

I'm leaning towards it simply blowing out past the filler cap, since if I attach a container to the overflow, it fills up when the problem occurs.

Is it possible to get a higher pressure one that would fit? Existing says 15 psi.

What I haven't done is to pressurize the system via the rad filler, to check the cap does hold at approx 15 psi. Will have to make a filler cap to do that, as my kit doesn't include one that fits.

Dave, Is the metal sealing ring in the expansion tank pitted with corrosion like a lot I've seen?

Mine has air-con, so the header tank is brass, rather than plastic with a steel seat for the cap as on others. And it looks OK. I suppose it could be worn in some way at 30 years old.

But I'll make up a way of pressurizing things with the cap in place.