radiator cap double working on a V8 engine

J

Joop

Member
Hello. I am looking for a radiator cap f (1,5) for a rover 3500S who is double acting because i put an expansion tank on the car. This expansion tank is a overflow tank (from a susuki alto) and is from plastic with a plastic cap.
Has somebody an idea? Is it wise to put away the coil of the orginal cap (somebody advice me) so the fluid can go higher and lower in the expansiontank? I think the bioling point will than be reached sooner?
 
Hi, Is the plastic cap on the new tank a pressure cap? If it is then you need a blanking cap on the radiator so the coolant can expand and return as it needs.

Colin
 
Yes, the pressure cap goes only on the expansion tank. For the rad buy a blank or if you have any old cap around, cut the spring loaded center out. It only needs to cover the hole and not leak.
 
The cap is of the overflow tank is not an pressure cap. It is a cap that you click on the tank like the one the cap of the windscreen washer reservoir.
 
You would have been better off fitting an overflow tank from something like an old Sherpa Van and using a blank cap on the radiator and plumb the radiator overflow outlet to the Sherpa tank and use the pressure cap on that. Did this mod to my Morgan 4/4 years ago, it worked very well.
 
Don´t think, that you get aware of a Leyland Sherpa in Holland :D, but the expansion tank of a Rover 111 does the job as well (read this in an article in the Motor-Klassik).
Greetings from Germany (I´ve got my P6 from Holland last year :))
 
Going back to the original question using a none pressurised expansion bottle, the Land Rover S3 used one, so a cap from that might do (STC4735), but not sure if it is the same size or pressure. It has both a pressure seal and a seal to the rim of rad. opening, so a vacuum will draw coolant back from the bottle into the radiator.
Land Rover Radiator Cap STC4735
 
That's your problem a V8 needs a 15lbs cap. I don't know of a V8 that used this. The SD1 used a pressure cap on a clear expansion bottle.
 
I used an SD1 bottle and put the original pressure cap on the bottle, whilst using a flat cap on the radiator.

I believe you need a vented type, but to be honest I am not 100% on that, and I have heard that sellers often aren't sure either. Might be worth giving these boys a call and having a chat about this cap?

Richard
 
I used a period metal header tank off a series LR Defender. Swapped my radiator cap to the header tank . Placed a blanking cap on the radiator. Result - no more or should I say less frequent fluid top ups. Should have done it 40 yrs ago.
 
hi.
what is the difference between an expansion tank and an over flow tank? are these terms interchangeable?

They both do the same job of collecting excess water from the radiator in one form or another!

If the "tank" is to suck the excess fluid back into the radiator it needs a "recovery cap " fitted to the radiator and a pressure cap to the "tank" ? (recovery cap has no spring to retain radiator pressure)....
if it is an "overflow tank" it just collects water and not resend it back to the radiator, so what is the use of this type of setup.............. not much I think!
the plot thickens...arhh aye me lad...o_Osucking on a straw from the meadows..
Peter

I used one of the solid type brass tanks from a mini on my Morgan and 35 Chevrolet std with great success. The bloke that I procured the tanks from said that these were the last of his hoard, so I had the honor of using the very last in Taree..........whoopee..
 
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