[Healeys] Pressure relief valve

[Bob Spidell]

Background: my BJ8 has run low oil pressure at idle for as long as I've had it. At startup I get 60psi, but after 
running on hot days I would register, for all intents and purposes, zero psi at idle. In spite of this, the engine has 
run and performed well for me for over 100K miles. I use 20W-50 dino oil.

There has been a lot of discussion on the BCF about replacement relief valve springs being shorter than spec.  It has 
been suggested that putting washers or other shims or a 1/4-inch bolt behind the spring could increase running 
pressure.  I actually didn't believe it because AFAIK the valve is there to keep pressure from getting too high, and 
presumably would be fully closed at normal running pressure.  But, I was curious ...

So today I pulled the relief valve and measured the spring at 2 & 11/32"; quite a bit less than 'spec.' So I installed 
the 1/4-inch bolt and fired her up; 70psi on cold start/fast idle--not too surprising. What's surprising is even after 
the engine has warmed-up--when I would normally see 10-20psi, before a long run in hot weather--I am getting 40psi. And 
the max pressure is still at 70psi; so the effect is max pressure is up 10psi, but the hot idle pressure could be up 
10-20psi!

My questions to the forum are: is 70psi too high a max oil pressure? Any explanations for this phenomenon? Should I 
split the difference with some shims?  Go back to the spring-only setup so I can sleep?

Bob

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Bob Spidell           San Jose, CA            bspidell at comcast.net

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