Oil pressure drop

[nick Godridge]

Hi all,
   
   My car is fitted with a stoker 302 giving 347 cu. inches.
   
   I have uprated exhaust manifold. Same as a factory lightweight, and slightly hotter road cam. Net result, lots of torque and somewhere in excess of 320+ horses. Also oil cooler fitted.
   
   Oil pressure in normal driving is generally rock steady around 50psi. However if I drive it at or over 3000r.pm. (roughly 100 m.p.h with my diff)in 5th for any period of time, I lose 3-4 psi at speed and around 10psi on tickover.
   
   Now, is this just because I am useing so much throttle, to maintain this pace, or should I look at the cooling again?
   Does anybody else see this effect, and if so have you taken any action, or, are you relaxed about it?
   
   Thx
   
   Nick G

[AC Ace Bristol]

.
   Nick.
   
   Atfer 20 minutes or so racing the Ace Bristol or pushing the Lotus Twin Cam hard the oil pressure drops 10psi or more at tick over and a few pounds less throughout rev band  due to temperature of oil circulating in engine and oil cooler. What increase in oil temperature do you experience[?] and what oil do you run [?].
   
   I change good quality engine oil and filter regularly irrespective of mileage.
   
   I wouldn't be too concerned , Mind you I don't run a V8.
   
   Keith..[]

[nick Godridge]

Thx Keith,
   
   No oil temp gauge on a mk1V unfortunately. maybe I should consider finding a way to get one fitted, but where?
   
   I run a Gulf ester based synthetic competition oil SAE 15-50.
   
   Nick

[Flyinghorse]

Nick,
   Is your oil cooler thermostatic or always in the system?  Have you checked its operating?
   
   The issue sounds viscosity/temperature related.  Would also check your timing at full advance to see you are not running retarded & therefore hotter.
   
   Graham

[nick Godridge]

Interesting.
   Cooler is always in the system. Would not know how to check if its working.
   It certainly gets hot.
   
   Nick.

[Flyinghorse]

Nick,
   I am assuming your engine has never done this before now?
   If the cooler is  hot oil will be circulating. Infra red heat gun is good for checks(dont like reflective surface so use electrical tape). You could take the cooler off & flush it through/clean it.
   
   You never mentioned you water temperature-has that also changed & what coolant do you run?

[nick Godridge]

Use a water/antifreeze mix, dayglo orange stuff that's designed for alloy engines ( aluminium heads), and cooling is not too bad. Does'nt like idling a long time in hot weather, but generally stays around 180.
   
   I can probably get hold of a 'temperature gun' what range should the oil be in?
   
   Should I compare the oil cooler temp to that of the sump?
   
   Nick

[ak1234]

I'm pretty sure ... Small Block Ford's oil pump has a relief valve / spring .. which at high rpm the pump relieves it self so you dont over pressure the system.

[Flyinghorse]

Nick,
   The problem is the cooling rate when moving--oil rate through cooler & heat exchange capacity  of cooler. WIll be hard to do just idling.
   The heat gun is just useful for checking input & output oil temp. (ie if you have flow through the oil cooler/radiator etc)
   I bought mine to chase a non existent overheating issue --it was just a poor temp guage.
   
   If you can get a chart for your oil of viscosity vs temperature ,you may see if theres a kickover point on the graph where the oil starts loosing viscosity as heat goes up.
   
   As your engine is modified are you sure your dipstick is the correct one for the sump pan you have. You may not have enough oil in the system. I have seen a lotus twincam wrecked this way.
   
   If it were me I would not be to worried  & put it down to the viscosity changing when oils hot. 3 psi is not much. We never measure oil flowrate but its likely that oil flow rate increases as viscosity gets lower even though you get a lower oil pressure.

[cobham cobra]

I did have a similar experience driving on the motorways in the South of France last year. At about 80 or 90 mph the oil pressure suddenly dropped by approx 10psi for a few minutes, it did this a couple of times during the trip. Each time, I backed off a little and the pressure slowly returned. It was high summer and the air temp was in the high 80s. It certainly got my attention when it happend and I had everything checked out when back home and nothing was found to be wrong with the engine or cooling. I have not noticed it happening since that trip and have since had the oil and filter changed.
   
   My engine is a 302 with a Holly 600, Edlbrock  performer heads, duel-plane intake, hotter cam and Shorty headers and has an oil cooler.
   John.

[3.5 Pints at the Bar]

As long as the oil is not too hot, then it is the rate of oil flow that is important. Pressure causes this flow, but as the oil heats up and becomes 'thinner' (lower viscosity), the pressure needed to get good flow reduces. So it might be okay, but an oil temperature gauge could be a good investment just to be safe.

[Superarnie Mk2]

Could it be that the stock oil pump isn't capable of meeting the needs of these engines especially if performance modified?? It may be worth considering a high volume oil pump??
   Gary