[Sidecarbod]

Originally Posted by dhennings

I am recommissioning a rover v8 engined LR roadster cobra. I have fixed all the problems except one. The engine is fine when blasting along but at tickover the levels of coolant soon rises in the exspansion tank and then it pushes out the coolant. However when it does this the coollant is not at boiling point - more like about 70c. It seems like an airlock is forming - I have tried bleeding the system at the highest point and there does seem to be air in it before it happens. The pump appears to be circulating ok - when you take a hose off it sqirts suggesting the pump is ok.

Originally Posted by dhennings

When the coolant is rising if you give ita good rev you can see the level in the tank drop about a half inch and then it rises back again as the revs fall - I assume that also shows the pump is working

I cannt work out why it is doing it or where the air is getting in from. I am going to do the test on exhuast gases in the water but if it was that it would surely be worse at high speed?

If the cap on the surge tank was faulty would that do it? Could the pump still be faulty?

Any ideas gratefully recieved

The top hose is the usual cultrate for airlocks, you need to make sure that it is as straight and low as possible.

Your manifold may also be a problem depending on what type it is. The Edelbrock performer has a problem in that it can shield the thermostat from the hot coolant to the point where it does not open at the right time. If you have an Eddy manifold let us know so we can explain the simple fix. (Cue Graham and his wiki!)

Some header tanks have a filler neck that is too long, this totally messes up the blow off pressure of the rad cap, again this can be sorted.

Some thermostats don’t have any bleed holes, a lot of air can get stuck behind them. If yours does not have a hole then you can drill a 3mm hole in it. I would also run a 74 degree stat if I was you. (Assuming that you’re not running EFI). The engine will then run at about 80 odd degrees which is fine for an RV8

Like Kevin said some info on the design of the header tank would be useful. Basically the term “header” is often used when the tank is really an expansion tank, it all depends on how it’s plumbed in. For example the pilgrim setup uses an actual header tank and that is prone to problems due the size and location of the air bleed at the top.

I bleed my system by running the engine with the header tank cap off, I rev the engine whilst standing next to the tank with a supply of coolant, the level in the tank will drop as the air escapes out of the system via the open top of the header. Each time it drops I refill the tank to about 2/3rds full. When the level does not drop anymore I fit the cap back on and go for a drive. When the car is back in the garage I let it cool down then re-check the level, if it’s not at 2/3rds I top it up again. After that it won’t need any more coolant.

HTH,

Pete