Thorney Old Problem where to put the Pressure Cap
Discussion
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!
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!
Looks to me like the wrong cap is recomended, and what is required is a recovery type.
The following thread explains the two types, not read it all but it has good pictures.
http://www.mgcars.org.uk/mgccz/technic/pressure_me...
The following thread explains the two types, not read it all but it has good pictures.
http://www.mgcars.org.uk/mgccz/technic/pressure_me...
Griffinr said:
Looks to me like the wrong cap is recomended, and what is required is a recovery type.
The following thread explains the two types, not read it all but it has good pictures.
http://www.mgcars.org.uk/mgccz/technic/pressure_me...
Interesting read.The following thread explains the two types, not read it all but it has good pictures.
http://www.mgcars.org.uk/mgccz/technic/pressure_me...
I also had problems with a new pressure cap but when the old one was back on - problem sorted.
Gerald-TVR said:
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
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.I'm convinced its all down to the pressure cap design, would just LOVE to bottom it out and put the discusion to bed
If anyone wants my full explantion of how the two methods BOTH work then search for my original explanation.
Mark
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 knowledgeso the saga rolls on
clarenceboddiger said:
If the pressure cap was to be put on the swirl pot and the expansion bottle fitted with the non pressure cap then the water dispersed into the expansion bottle would just evaporate to the atmosphere over a period of time
That's why I have a 15lb pressure cap on the swirl pot and a 13lb pressure cap on the expansion tank.I can see this thread exploding all over again, you've done it now Norman
Cheers.....Tony..
tozerman said:
clarenceboddiger said:
If the pressure cap was to be put on the swirl pot and the expansion bottle fitted with the non pressure cap then the water dispersed into the expansion bottle would just evaporate to the atmosphere over a period of time
That's why I have a 15lb pressure cap on the swirl pot and a 13lb pressure cap on the expansion tank.I can see this thread exploding all over again, you've done it now Norman
Cheers.....Tony..
tozerman said:
clarenceboddiger said:
If the pressure cap was to be put on the swirl pot and the expansion bottle fitted with the non pressure cap then the water dispersed into the expansion bottle would just evaporate to the atmosphere over a period of time
That's why I have a 15lb pressure cap on the swirl pot and a 13lb pressure cap on the expansion tank.I can see this thread exploding all over again, you've done it now Norman
Cheers.....Tony..
Just in case anyone is in any doubt to Norm's comments about professional credentials above I am the head of a Design Authority who specialises in pressurised fluid systems within the MoD, so I do know what I am talking about when discussing pressurised coolant systems. Didn't really want to post that here as could seem pretentious, but this can of worms keeps on getting my goat I am afraid.
If Adrian's comment is correct it does mak sense, but then this is really down to TVR's poor workmanship in sealing the unused sensor hole in the expansion tank. This is because as I understand it the Triumph Herald that uses this expansion chamber as OE equipment also fits a 15psi cap to it, so the TVR bodge to seal the unused sensor is the only bit that could not be up to spec.
Mark
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