150 Sigma Expansion Tank

[Luegonigel]

I'd assumed there was an airlock in the engine somewhere due to the coolant level rising in the expansion tank.

A bleed tee is fitted in the top hose of the radiator, near the radiator.

I unbolted the expansion tank and lifted it above the bleed tee and the radiator. On removing the plug from the top of the radiator found there was a lot of air at the top. Plug put back in when water rose to top. Removed bleed tee cap, no air in that bit, only coolant came out. Filled expansion tank to correct level, put cap back on, then lowered the tank down and bolted it back on.

The expansion tank cap is brand new.

After a couple of runs, tank level has gone up 25mm and doesn't seem to have gone back down even when the engine has cooled.

Is there still an airlock somewhere, is it sucking in air somehow, other?

What else to check?

[Jonathan Kay]

Filled expansion tank to correct level, put cap back on, then lowered the tank down and bolted it back on.

I haven't got a Sigma and the procedure may be different... but should that filling level be used when the tank is down in position rather than held high?

Jonathan

[Luegonigel]

Jonathan, when I take the cap off the tank with the tank bolted to its normal position, the water in the heater hose runs back down into the tank as the heater hose is heigher than the fill level. This then introduces more air........unless I'm missing something.

[IanReeves]

Just put a new radiator in my Sigma,

Back filled the heater with it disconnected with a short length of hose and with it all re connected Lifted the whole front of the car as high as possible.

I got a big 'glug' and the level went down about an inch or so.

Topped upto the max level and ran the car for 15 mins until the fan cut in, it's been fine. Temp is stable as it level.

I did replace the two plastic Tee's as recomended by everyone.

[RedCat7]

Seems like you still have the same problem you had last year?

http://www.lotus7.club/forum/bleeding-sigma

If the plug is still fitted in the top of the radiator then I guess you never got around to re-introducing the bleed-line from the radiator to the tank? 

This is how my plumbing has looked for the last year and I've had no more cooling issues.   I recently replaced the other plastic tee and on refilling I had no problem with air locks.

[Luegonigel]

Thanks for jogging my memory, I did buy the bits but didn't fit them, I discovered them in a drawer in the garage. I then realised I didn't have the right size jubilee clips so that is why I must have stalled.

Will be bought and fitted tomorrow!

[Luegonigel]

Bits fitted, 700 miles done, water level now remains fine. Small leak somewhere.

The banjo fittings I got looked a bit cheap and nasty, initially couldn't get the copper washers to seal so changed to Dowty washers (different thickness). Have now bought some better quality banjos which look more like an engineering component + some fibre washers of the right size. Will change over when I have five minutes.

[RedCat7]

I used also dowty washers and it's been a case of fit and forget. The only downside of the dowtys that I can see is the thickness which means less thread engagement so you need to be careful not to over torque and strip the threads.