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.
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
