High oil pressure

[mdburchette]

I am wondering if it is necessary for a Fiat twin cam 1608 to have such high oil pressure. I have a newly rebuilt engine that is showing 80 lbs of pressure at idle and goes up to 90 lbs while revving during break in. The previous 1608 we built has had high oil pressure as well, so I don't think it is due to too tight of tolerances or a blockage.

[Guy Croft]

No, it's so high I anticipate the oil pump shaft shearing under the strain, or the cam seals blowing out/leaking.

These engines will run 'forever and a day' if provided with a continuous flow of oil at 55psi (hot) and that would typically be a higher figure when cold, say 65-70psi and of course the pressure drops as the oil warms up.

The output of the gear pumps goes up-and-down with speed, 15-20psi is perfectly adequate at hot idle, say 25-30 on cold start, I've wouldn't really want higher than 70psi hot at high rpm (6000+) and I have run engines with that figure.

I suspect the relief valve spring is either wrong or has been packed up too much,

GC

[mdburchette]

Thank you for your response, Guy. I understand, by the owner's manual, that high oil pressure is not unusual (55-75psi). We replaced the oil pump on the initial build and had a problem with it seizing, which caused the auxilliary shaft to seize and damage the #2 rod bolt by hitting the fuel pump lobe. We replaced the oil pump with another new one.
I'll keep an eye on the oil pressure to see what happens.

[Guy Croft]

I'm not suggesting that you necessarily caused the breakage Denise, I know how careful you are, but I'll just remarkthat it's vital to rotate the aux shaft while you are bolting up the pump - this is true of all the TC and SOHC models except those with crank-nose driven types - there are no dowels to locate the pump body accurately co-axial with the driven gear (that runs off the aux d/s) and if the pump shaft is out of alignment and thus tight/binding in the bronze bush in the block it will shear sooner or later.