Cooling System Problems

[R2D2]

I have a Lotus Twin Cam engine in my Seven which has been re-built with a new head etc, etc and I still seem to have some cooling problems that are worrying me.

 

The cooling system is identical to the system that of the crossflow engined Supersprints.

 

I have the cast aluminium thermostat housing with the double-sealed radiator cap that also has a vacuum vent. (A 74degC Thermostat is fitted). There is an un-pressurised expansion tank from the overflow, which I keep half full and keep the overflow tank below the water level. The system has been completely bled and doesn’t have any airlocks. I have been running the car with the heater valve closed. All of these parts are new and the car has a four row alloy Pace Products rad fitted.

 

The temperature gauge has been check calibrated and indicates a temperature of about 75deg while moving and about 90deg in traffic when the fan cuts in correctly. It all seems to be running well and without problems.

 

When I check the water level with engine cold there is always a very slight positive pressure in the engine and this blows the small amount of water above the thermostat into the expansion tank and I don't think this should be happening.

 

I would expect that the vacuum valve should draw water back from the expansion tank into the block until the pressures were equalised.

 

It seems to me that the only source of pressure build up in the block could be from a head gasket problem as any thermally driven pressure build ups should be completely reversible. (adiabatic?)

 

I have checked the engine with a Snap On block tester which tests for the presence of hydrocarbons in the coolant and everything checks out as perfect but I am still concerned.

 

Help! please

 

[allen]

Chris,

 

Whilst not an expert, my own experience with the 'no loss' expansion tank system is that gradual loss of coolant does occur, and it is never all sucked back in on cooling down. Often air does find it's way back into the engine, don't know how.

 

The newer type of 'no loss' pressurised expansion/header tank system works much much better and I am sure it can be fitted to a Twink. I converted when I changed from the xflow to zetec.

 

Regards,

 

allen

 

 

 

Edited by - allen on 10 Sep 2001 09:06:57

[Tony Martyr]

Chris, Your concern about the locking in of residial pressure in the coolant system is interesting but given you have not got any objective sign of gasket leakage it may be missplaced.

The pressure build up caused by heating of the coolant is not entirely reversable as there are a number of marginal events occuring. What you are seeing is probably the effect of storage of pressure energy through the elastic deformation of various parts of your cooling system pipes. I certainly see it on my k series unit.

[Muttley]

Chris,

 

Could you pleae explain what you mean by double-sealed rad cap? Do you mean as well as the pressure seal, the cap also seals to the top of the thermostat housing?

[R2D2]

Tony, I was hoping that my concerns were misplaced but driving modern cars for the last few years has meant that I don't think I have checked the water levels for about 15 years. When I bought my Caterham I had a significant number of cylinder head problems which cost quite a lot of cash to sort out and I would accept I have become too preoccupied.

 

Your comments about residual pressure are exactly what I was hoping the hear and give me a great deal of comfort.

 

Muttley: Yes that is exactly what I meant, I am sure there is a more formal description, but I don't know what it is.