Thorney Old Problem where to put the Pressure Cap

[Gerald-TVR]

I dont want to open a huge can of worms- again but I have had some thoughts (I know I know a rare occurance)

Most usual method is for the pressure cap on the swirl pot and the non pressure cap on the expansion tank. The water level stays just about an inch above or level with the exit hose at the bottom of the container and runs fine with no further additional water. This is exactly what I would expect to see and the situation I found on my car.

BUT if you are finding that the water level continually drops to a point about 1/4 to 1/3 down the swirl pot then the pressure cap (in my opinion) is suspect as it would appear NOT to allow coolant back into the swirl pot as it cools down. If the pressure cap is on the swirl pot then it must allow 'tidal flow' back from the expansion tank. If you have a tidal flow pressure cap then the caps can be either way around. If the pressure cap dosent allow the tidal flow it must be on the expansion tank.

At one point a new pressure cap was fitted to my car and the swirl pot needed constant topping up, swaping back to the old pressure cap resolved the issue

I suspect that some pressure caps allow the tidal flow (and I would guess they are likely to have the rubber seal just below the cap) and others dont. Now its been said frequently that you have to cut an extra seal and I do wonder if those caps dont allow the tidal flow.

Just some thoughts, I agree with previous posters that both variations work but I would love to investigate further and see if I'm right about the tidal flow, or lack of it.

I have spoken to Quinton Hazell tech support today and they have confirmed that both the FC52 and FC53 (normally quoted for the V6 S) do NOT support tidal flow

I now stand back and await the barrage of disagreements!

[Gerald-TVR]

Roys post with the TVR note is fine but will have to rely on the correct type of cap, tidal flow or recovery type, to be fitted.

Usefull article from the MG boys seems to confirm my thoughts

Edited by Gerald-TVR on Wednesday 25th November 16:54

[Gerald-TVR]

Hi Mark

I'm convinced its all down to the pressure cap design, would just LOVE to bottom it out and put the discusion to bed

[Gerald-TVR]

Jed-S said:

The QH FC53 caps that I've used do have vacuum relief valves.

When i spoke to QH yesterday they actually said the opposite

mep12345 said:

As I said on the phone I agree the key is the cap if you want to put it on the swirl pot as it must then relieve the vacuum as per the MG note above. However,if you put the pressure cap on the expansion pot it doesn't matter, but one without a vacuum relief is probably better to reduce air ingress paths.

Totally agree and to your technial knowledge

so the saga rolls on

[Gerald-TVR]

Dont you just love it when a plan come together

[Gerald-TVR]

Adrian - no problems and the difference between the FC53 and FC60 is ?????

Edited by Gerald-TVR on Thursday 26th November 23:06

[Gerald-TVR]

Adrian@ said:

OH Norman....I just cannot resist any more....FC7 ....I thought someone might of replied by now with the QH info.
Adrian@

Edited by Adrian@ on Friday 27th November 08:39

Should have known better

[Gerald-TVR]

mep12345 said:

I will not respond to the pressure cap threads again
I will not respond to the pressure cap threads again
I will not respond to the pressure cap threads again
I will not respond to the pressure cap threads again
I will not respond to the pressure cap threads again
I will not respond to the pressure cap threads again
I will not respond to the pressure cap threads again
I will not respond to the pressure cap threads again
I will not respond to the pressure cap threads again

You'll be back

[Gerald-TVR]

Had they both ways round. Worked fine except when i had a new pressure cap on swirl pot and lost coolant - put the old cap back and it was fine