View single post by Esprit2
 Posted: 08-01-2016 02:23 am
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Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 341
907 Oil Pressure Specs

Jensen-Healey at normal operating temp (hot)
60 psi (4.2 kg/ sq cm) at 2500 rpm

J-H's 60 psi oil pressure spec is possible, but not normal, especially if the engine is now old with a lot of miles on the clock. Looking for 60 psi will result in a lot of un-necessary disappointment.

Lotus at normal operating temp (hot)
Not below 5 psi (0.35 kg/sq cm) at idle
Not below 35 psi (2.5 kg/ sq cm) at 3500 rpm
Not below 45 psi (3.5 kg/ sq cm) at 6500 rpm

Lotus' specified minimum oil pressure at idle scares me. No 'healthy' 907 will have oil pressure that low, and 5 psi at hot idle clearly indicates something isn't right.

All Lotus engines prior to the current Toyota powered cars use main and rod bearings with rather wide tolerances. The design depends upon a high viscosity oil (20W50 / 10W60) and an oil pump that can deliver a large flow volume at a modest pressure. High pressure is not a design parameter, and it is not necessary to shim the relief valve's spring to achieve 60 psi at 2500 rpm.

Modern engines must meet mandated efficiency standards, so they're using thinner oils... like 0W20 to 5W30. Those thin oils require much tighter bearing clearances, and higher oil pressures. Just because some modern, thin oil works great in your new daily driver doesn't mean it will work great in your 907. It won't!

Keep the viscosity up, and hot oil pressure of 35 psi is reasonable on the street, maybe 45 psi on the highway, and 50+ on cold start-up. 60 psi hot is not necessary, or even good.

Tim Engel

Last edited on 08-01-2016 02:27 am by Esprit2