Radiator Pressure Caps for B18 &B20

[Groundes-Peace]

I see Brookhouse sell two different radiator caps for the B18 and B20 engines, although the radiators for each engine on the 1800S cars appear to be the same.
Are these with different pressure tolerances? If so what are these?

[Ron Kwas]

G-P;

B18s with what I will call an "Old-Style Cooling System" (that is, no Overflow Bottle), had the Pressure Cap on Radiator (when Cap pressure is exceeded, overflow dumps to ground).

I believe later B20s in most markets had "Sealed Cooling Systems" (with Overflow Bottle). These had a simple sealing cap at the Radiator, and Pressure Cap was located at Overflow Bottle.

I do recommend retrofitting early B18s equipped vehicles with Old-Style Cooling Systems with an Overflow Bottle and upgrading the system. See: http://www.sw-em.com/service%20notes...oling%20System

Cheers

[swedishandgerman]

Originally Posted by Groundes-Peace

I see Brookhouse sell two different radiator caps for the B18 and B20 engines, although the radiators for each engine on the 1800S cars appear to be the same.
Are these with different pressure tolerances? If so what are these?

Yes - B18's with expansion tank system ran at 4PSI, then they changed to running at 10PSI when they changed to B20's, so there are different caps for the 2 different engines. As far as I know, there's no reason why you shouldn't put a 10PSI cap on top of the bottle of a B18, but dropping from a 10 to a 4 would be a step backwards.

There's no reason the B20 needs to run at a higher temperature and there's no feature in the system that makes it do so other than the cap. In other words, the cap will allow the air to expand to 10PSI before it's valve opens slightly to relieve pressure. The reason for this modification is because liquid under pressure boils at a different (higher) temperature, so a bit more pressure altered the boiling temp. The valve is there to deal with over pressure should the liquid start boiling as the system will explode under pressure without it! The expansion chamber is there so that pressure builds up as it gets hot and the liquid expands. Personally, I never fill up an Amazon's expansion tank to max when cold. Instead, I check it when it's really, really hot and aim for it to be at the max line then. Of course, I don't add when hot, but if it's say 4cm from the line when hot, I add say 2 or 3cm when cold. That way - this is just based on Adam theory - the pressure is just right with the maximum amount of cooalnt in the system without any danger should the thing overheat.

I don't know the pressure the old style pressurised system without the expansion tank runs at, but I doubt it's as high as 10PSI as I don't see how it could handle it.

[Groundes-Peace]

Thanks for the very full explanation. This has been helpful.