Rad cap pressure

[andyf]

I'm wondering if there's any harm in switching from a 13psi rad cap to a 13psi version. My problem is that it's venting coolant out of the overflow...

[Alan c]

Re: Rad cap pressure

No problem they are identical both being 13 psi !!!!

Typo me thinks

[danny_nelson]

Re: Rad cap pressure

Have you got an overflow container or an expansion fitted?

[stevejgreen]

Re: Rad cap pressure

Putting a higher pressure cap on will increase the water temperature as well as increasing the water pressure.
It is possible that the higher temp may cause poor running especially if you have EFI, and the higher pressure may find weak spots in the cooling system.
Presumably you have an updated Chevette radiator. The radiator cap should be a double seal type so that as Danny indicates any overflow water can be sucked back into the radiator from the overflow container/expansion tank, when the radiator temperature drops.

[andyf]

Re: Rad cap pressure

No problem they are identical both being 13 psi !!!!

Typo me thinks

That's right the second 13 was supposed to be a 15

[andyf]

Re: Rad cap pressure

Putting a higher pressure cap on will increase the water temperature as well as increasing the water pressure.
It is possible that the higher temp may cause poor running especially if you have EFI, and the higher pressure may find weak spots in the cooling system.
Presumably you have an updated Chevette radiator. The radiator cap should be a double seal type so that as Danny indicates any overflow water can be sucked back into the radiator from the overflow container/expansion tank, when the radiator temperature drops.

It's running around the 80oC mark at the moment. Finding weak spots in the cooling system was exactly what I was thinking about. As for the radiator I believe it was a standard Viva HB radiator as it's only got a single seal on the rad cap so there'd be no sucking back I never fitted an expansion tank because the original cooling system didn't have one and there wasn't much space left to fit one

[andyf]

Re: Rad cap pressure

By the way I noticed that Burtons sell a 28PSI cap for a Pinto!!!!!

[John_Mulvaney]

Re: Rad cap pressure

Andy, under what circumstances is coolant being lost?
Kit car coolant plumbing is unlikely to be as the designers of the engine intended! In my mind an expansion tank that allows coolant to be drawn back into the system as the engine cools is essential in order that trapped air can purge itself as it expands and contracts - several small top-ups of coolant after short runs may be needed.
Whilst towing a caravan with either of our 3.9 or 2.3 Cabrios (or a 2.0 Pinto Rickman for that matter!) running temperature was fine, but turning off a hot engine could cause coolant to be lost. I think this could be due localised boiling around the exhaust valves once the coolant circulation has stopped. A higher rated pressure cap on a pressurised expansion tank overcame the problems, but all was in good condition and working as it should, in particular the (radiator filler) blanking cap and the pressure cap itself.
If coolant is being lost whilst the car is in motion this indicates that insufficient heat is being dissipated and I would suggest making improvements to this aspect before increasing the pressure of the system.
Hope this helps,
John

[danny_nelson]

Re: Rad cap pressure

Andy, an expansion tank is ideal in the system. On the Ford pinto you can get a thermostat cover with a pick up or you can sort several alternatives. Otherwise an overflow bottle will do, so you have no coolant loss. Everything as stated above is relevant as well. Pinto with carb runs fine around 80/ 85

[andyf]

Re: Rad cap pressure

It's losing coolant in motion as it were, it's blowing past the rad cap. On the way back from Cornwall we got stuck in a traffic jam for over an hour and the cooling system worked fine with the fan switching on and off at regular intervals. Now the rad cap is 30 years old so the rubber is quite hard and has a well defined groove in it so I'm going to replace it anyway so I'm wondering wether I'm better off going for a standard Viva HB cap which is rated at 15PSI or a Cortina one which is rated at 13PSI. Does anyone know if they are different dimensions? Or are they physically the same?

An expansion tank would require some modification to the plumbing because the overflow pipe does not have a good seal. The other issue is that I can't simply swap my therostat housing out because it was modified to suite the installation

[danny_nelson]

Re: Rad cap pressure

Same dimension.

[andyf]

Re: Rad cap pressure

Thanks guys, I've gone for a 13lbs rad cap that has the double seal. If I can sort out the overflow I may add a catch tank as well.

[John_Mulvaney]

Re: Rad cap pressure

Does sound as if you need that new cap Andy - you don't seem to be describing a "boiling over" situation due to inadequate cooling.
I cannot imagine that a 2psi increase in system pressure will find too much more in the way of additional leaks but should give around an extra 14 degree C before the coolant actually boils and the cap is called on to do it's job of venting excess pressure, regardless of where the coolant ends up.

[dbazdavies]

Re: Rad cap pressure

This seems a good buy and its the same size as the rad in my Marlin

http://www.ebay.co.uk/itm/221987502723?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

[stevejgreen]

Re: Rad cap pressure

This seems a good buy and its the same size as the rad in my Marlin

http://www.ebay.co.uk/itm/2219875027...%3AMEBIDX%3AIT

Beware the standard Civic radiator, most of that era were 1600 engines or smaller, the clue is in the engine codes D15=1500 D16=1600. There is an uprated version that should be OK.
I notice that there is a fan and shroud kit available for these radiators. I wonder if that would fit in the nose cone of a Roadster.

Ref Pitstop 171 Aug Sept 2012