Marina rad cap

[FranklinLeicester]

I have just noticed that Marina 1300 rad caps on Ebay are listed as 13 or 15lbs. Mine has 7lb job but can't say I've had any trouble. Does the fact that we use Vauxhall rads make any difference?

[CABRIOBOB]

Re: Marina rad cap

The 13lb cap is the norm, but nothing wrong with a 7lb cap, but it will only blow off sooner when the water temp gets to hot as it increases pressure which then allows the cap to open up, more so when the cylinder head gasket is leaking on the cooling side.

[stevejgreen]

Re: Marina rad cap

The cap controls the coolant pressure. A 15lb cap at about 125 deg C, Its a linear curve down to an open system at 100 deg C. so 2.5 deg C per Lb.

The Roadster is wildly different from a Marina in radiator size and airflow so its a bit of trial and error. If the engine gets too hot, under high pressure the risk is that you blow pipes and gaskets. The hotter the engine runs the more likely you will get poor combustion and excessive pinking.

Worth saying that the thermostat has very little control over normal running temperature. Most are fully open at 103 deg C long before the engine is at its normal running temperature. Their duty is to speed engine warm up, and little else.

[gary.price]

Re: Marina rad cap

Hi sorry to highjack the thread but what caps do i need for my roadster?? they dont have the seals on them which probaly has alot to do with my coolant loss lol.

[stevejgreen]

Re: Marina rad cap

Its difficult to help without info.

Marina? Triumph? 1300? 1800? other?

Are you trying to put a Marina cap, designed for a Marina system on a radiator that does not have an exansion tank?

Have you a standard Marlin Chevette radiator or a modified 3 core or one of the many alternatives like a Landcrab?

Without knowing what your radiator/cooling system is it is difficult/impossible to give accurate advice.

There are many tales around cooling/overheating coolant loss on this forum, and a very few answers that have proved reliable.

[gary.price]

Re: Marina rad cap

Oh sorry its a 1.8 mgb engine. I have a standard viva rad with expansion bottle. But have just noticed looking at the caps they don t have seals on them. So the system dosent really pressurise.

[stevejgreen]

Re: Marina rad cap

Step one. Take the radiator out and have it re-cored. Three cores are better than two. If you are feeling rich, use it as a pattern for a bling new aluminium radiator. It will cost around three times as much.

[CABRIOBOB]

Re: Marina rad cap

Gary,
Just fit a 15lb cap with a rubber seal to the radiator, this should be ok. A 3 core rad will help if you are having overheating issues. Give me a ring if you want any more help.

[gary.price]

Re: Marina rad cap

Thanks guys il try a new cap first. im not really having overheating issues cause iv added a second heater matrix from a old land rover. I just thought it was werid that it didnt have a seal on either of the caps.

[CosworthCabrioLee]

Re: Marina rad cap

Nice stainless steel ones on eBay look under marina radiator cap

[CosworthCabrioLee]

Re: Marina rad cap

200519975469 15lb stainless steel

[FranklinLeicester]

Re: Marina rad cap

Gary and Seve, That confirms my thoughts regarding pressure etc. My expansion tank doesn't have seals in either but as this container is not pressurised it wouldn't need one - correct Steve?

[stevejgreen]

Re: Marina rad cap

Assuming you have a open vented expansion bottle connected to the radiator filler neck, and not a pressurised expansion tank that you find on modern cars....

A double sealed cap is needed, something like eBay item http://www.ebay.co.uk/itm/VAUXHALL-V...item45f38b53c6

The idea is that the pressure forces water out of the bottom seal through the overflow but a vacuum is held by the top seal to draw water from the expansion tank back into the rad.

Without a top seal, the vaccum will dissapate and water will not be drawn back.