P38 expansion tank cap.

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Armyair

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My P38 has had a plethora of cooling leaks and now the system appears to be over pressurised and loosing coolant. I decided to change the expansion tank cap and as the new one had a pressure of 140 on it and the old 200 I am hoping this will solve the problem. Any ideas as to the correct cap pressure for a 4.6 rover lump. If this doesn't nail it I'm stripping the radiator then the heads.
Many thanks in advance.
 
The RAVE Manual states the Pressure release is set to 1.4bar or 20psi....

Not sure what 140 or 200 indicate....I am about to try and find my LR Parts MicroCAT and load it up to see if there is anything in there....
 
Saint.V8 said:
The RAVE Manual states the Pressure release is set to 1.4bar or 20psi....

Not sure what 140 or 200 indicate....I am about to try and find my LR Parts MicroCAT and load it up to see if there is anything in there....
Click to expand...


Where does it say that. My RAVE says "Cap pressure 1bar 15psi". Actually 14.7 but 15 near enough. Cap for petrol and diesel same part number PCD000070. If 140 and 200 are Kpa somebody better be careful. Because 140 Kpa is 20.29 psi and 200 Kpa is 28.9 psi. Maybe the 140 and 200 are just mold numbers who knows. General spec data 04 page 12.
 
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RAVE....Coolant Section for Land Rover V8....

Section 26 Page 4....image attached....

Just read your Section 4 Page 12...mine too says Expansion Cap Pressure 1bar (15psi)....

hmmmmm....

Still trying to find my copy of MicroCAT....
 

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Saint.V8 said:
RAVE....Coolant Section for Land Rover V8....

Section 26 Page 4....image attached....

Just read your Section 4 Page 12...mine too says Expansion Cap Pressure 1bar (15psi)....

hmmmmm....

Still trying to find my copy of MicroCAT....
Click to expand...

Think somebody dropped a bollock. 15 Psi is about standard for pressure caps. :):):)
 
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Saint.V8 said:
I thought 14.7 or 1 bar was about standard too...

Found MicroCAT just trying to install it now and see what that says if anything!!!
Click to expand...

Yeah 15 psi about standard these days, used to be 7.5 psi long ago, then on some went to 10. 15 for a long time now since they started running hotter engines. Old stats used to be 74 Degrees summer 84 winter. Now everything is 89 all year round. Hence the pressure rise.
 
Thanks for the debate. The value is on the pressure relief part of the cap and so I assumed it was related to a pressure value or scale.

It is a different colour and value on it which surprised me. Well I've ran it upto temp with the new cap and their was no pressure on releasing the cap when it cooled down which is a bonus but we'll see after its been for a half hour run tomorrow.

If anybody figures the 140 / 200 value I'm intrigued to learn.
 
OK after a few hours of searching.....

the figure is the burst pressure of the cap....

When I say burst, it doesn't mean it is going to exploded, it is the maximum pressure it will take before the releif valve won't close again....

i.e.

The cap is set to maintain 14.7psi at all times by relieving internal pressure.....if the cap can't exhaust the pressure fast enough and the pressure continues to increase, the relief valve is set to permenantly open at a given pressure and not reseat...so a new cap will be required.

The measurement is in Kilo Pascals (kpa) so 140 is 20psi and 200 is 29psi

Anyone else got any further with this explaination??
 
Saint.V8 said:
OK after a few hours of searching.....

the figure is the burst pressure of the cap....

When I say burst, it doesn't mean it is going to exploded, it is the maximum pressure it will take before the releif valve won't close again....

i.e.

The cap is set to maintain 14.7psi at all times by relieving internal pressure.....if the cap can't exhaust the pressure fast enough and the pressure continues to increase, the relief valve is set to permenantly open at a given pressure and not reseat...so a new cap will be required.

The measurement is in Kilo Pascals (kpa) so 140 is 20psi and 200 is 29psi

Anyone else got any further with this explaination??
Click to expand...

Sounds good to me, thought it was Kpa. Sounds right now as burst pressure. :):):)
 
Saint.V8 said:
OK after a few hours of searching.....

the figure is the burst pressure of the cap....

When I say burst, it doesn't mean it is going to exploded, it is the maximum pressure it will take before the releif valve won't close again....

i.e.

The cap is set to maintain 14.7psi at all times by relieving internal pressure.....if the cap can't exhaust the pressure fast enough and the pressure continues to increase, the relief valve is set to permenantly open at a given pressure and not reseat...so a new cap will be required.

The measurement is in Kilo Pascals (kpa) so 140 is 20psi and 200 is 29psi

Anyone else got any further with this explaination??
Click to expand...
Hey professor,cheers.i like it when.you do that but i hate physics
 
Thanks, that makes the values clearer. Now I'm wondering which burst pressure 140 or 200 is correct for my 4.6 as I think possibly my old cap wasn't relieving the pressure.
 
Armyair said:
Thanks, that makes the values clearer. Now I'm wondering which burst pressure 140 or 200 is correct for my 4.6 as I think possibly my old cap wasn't relieving the pressure.
Click to expand...

Some time ago, maybe in the late nineties, BMW did a recall on all their vehicles to change the rad cap. It had a fault. Don't know the reason, but i think it was either blowing off to early or too late. So don't know if the 140 Kpa is the new version or the 200 Kpa is. Maybe you can find out on BMW forums. I know about this because i had a 520i at the time.
 
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