Radiator cap woes

[peters3103]

Hi all,
I am still having trouble getting a radiator cap that fits my header tank properly. I bought the tank from SNG a few years ago now. The new 4lb cap they supplied me didn't even seat in the tank so it purged coolant almost immediately. I notified them and they did a measure up and discovered they had a dodgy batch. The recess in the tank measures 13/16 and the cap length from underside to seal was 3/4. The replacement they eventually sent was marginally better but still unsatisfactory - it continued to purge but not as quickly so was holding a bit of pressure. Both these caps offered very little or no resistance to push down and turn. I recently bought a 7lb cap from Terry's Jag Parts and fitted that yesterday. Went for a 30 minute drive and pulled up to find coolant spewing out again. When cool I checked the level and had to put over a litre in just to cover the baffle. The car doesn't run hot at all and I've gone back to a cap that was fitted to the car when I bought it. It's an unmarked after market job, almost square looking with 4 lobes, 1 in each corner for grip to remove/replace. I don't know what pressure it is but it works. I do however want one that looks original.

[Gfhug]

Not sure if this will help, but SNG have part number C18460 4lb pressure cap. C18484 7lb cap. Do these look correct to you?
I have suffered similar problems on my S2 and had assumed leaks elsewhere in the cooling system to explain the loss of coolant, but buying a new 7lb cap from them seems to have solved the problem.
From another thread it seems that purging excess coolant overboard was normal for the E and that the level can be expected to be lower than right to the top under normal conditions. Overfill and it purges.
In Britain there are several websites selling the same caps, so they don't seem special to the Jaguar brand.
Good hunting

[mgcjag]

Hi Guys.....are u overfilling the header......when cold top up to the half way mark on the header tank....7lb cap on expansion......plain cap on rad......13lb on air con cars....Steve

[peters3103]

Thanks for the replies, I've used both of those caps (4 & 7lb) which as I said measure up short - or is the header tank flange too deep? I'll have to measure up another to compare. I'm aware that it needs to purge to find its own level but mine continues to purge way beyond that. I did a round trip of 500 miles recently and put 2 litres of coolant into it. As I said it doesn't run hot and the non original cap works (it's longer in the spring and unknown pressure) but I would like to have an OEM cap.

Steve, the Series 1 cars don't have an expansion tank, the header tank simply purges via the overflow pipe to the road.

Cheers,
Peter.

[PeterCrespin]

I measured two S1 alloy header tanks, the expansion tank on my S2 and on my V12. All were 20mm / 3/4" ish from seal face to seal face. If yours is different you have a tank issue and need a non OEM matching cap.

[Gfhug]

Came across these which suggest they are longer, one says 1 inch/25mm. Bit more than your 13/16, but might squeeze in, maybe with a bit of fettling/adjustment.
http://www.angclassiccarparts.co.uk/hom ... -capri-1.3
http://www.minisport.com/grc101-radiato ... -neck.html

As Pete says, you may have a tank issue so need to go non standard, but these look the same as the SNG ones so are similar enough to look 'standard'.

Geoff

[peters3103]

Need to be careful that a cap with too long a spring isn't used as this wouldn't release pressure at all.

Pete