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New Engine Build And Now Getting 120 Psi On Oil Pressure

Started by postve , Jun 29 2025 10:04 AM

Best Answer Spider , 29 June 2025 - 06:51 PM

I think your gauge is wrong and leading you on a goose chase.

The Oil Filters are only rated to 100 PSI. At around 120 - 130 PSI the can deforms and will eventually rupture. Even at 100 PSI, you can feel it ballooning. I'd say here too that the 120 PSI is likely all that the sender will allow and if it was able to measure the problem - assuming there really is one - then the pressure will be higher.

If you have a high oil pressure problem, a very common cause for it being this high is the plug on the front of the block has been fitted too deep and it is blocking off the vent port at the back of the Oil Pressure Relief Valve. This one has a slot head plug fitted, but depending on your engine, this is usually a brass plug or a blind pop rivet

If that is in too deep, it will block off the passageway behind it and your oil pressure will be sky high, way over 150 PSI. At these pressures it's a race between the oil filter can blowing up, the oil pump gasket blowing out or depending on the oil pump, the drive for it shearing off.

One test for this is to leave the engine for a day or 2, so the oil will drain back, then remove the spark plugs and crank it over, at first, it will crank quickly, but wehn it gets 'wet' again, it will slow to a crawl, like hitting a brick wall.

BUT

I suspect your gauge is leading you up the garden path here.

Try a known mechanical gauge first before doing anything else. See what that's showing and we can do some more fault finding before going too far.

If you need to change the Valve, as Nick has mentioned do not use the Ball type, they are not suitable for road use;-

https://www.theminif...huttle-vs-ball/

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61 replies to this topic

#61 Spider

Moved Into The Garage

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Location: NSW
Local Club: South Australian Moke Club

Posted 04 July 2025 - 05:33 PM

Good work !

You might have a Cooper S Spring in there, they set the pressure around 75 mark. The stock Mini one was closer to 60, but as the engine is new, along with the oil, get a few miles on it before making any adjustments.