Want your opinion on what oil weight I am running

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Oct 22, 2003
By Detroit
When I got my mechanical oil pressure gauge in Sept I had a crankcase full of 5w30 dino. Pressure was 53 psicold, and hot was 36 @2000 rpm and 16 @ idle (700-800). Spec for this truck ('95 F150 300 I6 with 100,600 miles and runs great!) is between 40 and 60 at 2000 rpm hot. So then I filled the crankcase with 10w40 dino and the pressure is the same cold, but hot is 45 and 22. But really, I don't know that 36 was really all that bad. Maybe the 10w40 is overkill. If I back off I would probably go with a 10w30. Anyway, I am looking for your advice, opinions, suggestions and maybe I will make a change.
Spec is between 40 and 60 at 2000. You are running 45. What's the problem? You could go to a 15w-40 if you just wanted to run a little higher psi or something (??)
No problem. Just wondering is it really that important to run the spec oil pressure. Maybe a 10w30 would be better since it has less viscosity index improvers. Just thought I'd throw it out here for everyones thoughts. Yeah, I definitely could run a 15w40 in the warmer months. Might do that.
TallPall, I would not be conserned yet. You are not that far out of spec. with the 5W30. You might try 10W30 dureing winter and 15W40 dureing the warmer months. So long as your idle oil pressure stays above 8psi and the oil pressure climbs with RPM to within 10%of published spec I would just let it be! If the oil pressure affects UOA that would also indicate time to do repairs. Unless the engine has been abused with lots of sludge the oil pump is seldom the root cause of falling oil pressure. Most oil pressure drops are due to bearing wear! P.S. You did look for oil leaks? I once had a customer that had an oil pressure problem. TUrned out his distributor seal went bad and it was pumping oil out the distributor and that caused his oil pressure problem!
I believe that the 300Ci Ford inline 6 is one of if not the most durable engine ever built. I'd just drive the thing w/o a care to the world. It won't blow up unless you really try to kill it.
I would have to agree with Chris142. I would however stick with at least the 10w30, The 300 I6 tends to like a little bit thicker oil, I believe that 5w30 is a bit thin for this motor. What does Ford spec for viscosity in 95?
Preferred for the 300 is 10w30 above zero F and 5w30 below that. 5w30 acceptable anywhere below 60F. Oooooooh, what was I doing when I should have been reading my manual. I ran 5w30 in this thing for four years straight--year round! [Bang Head] Oh well, truck still runs great !!!!!! [Smile] Only thing is that the first oil chart in the manual is for the V8s and says 5w30 preferred at all temps. Possibly I read too fast and went on my merry way. Still I think the relief spring is more likely the culprit because this engine seems pretty tight and does not make noise or burn oil and has lots and lots of power. I'll stick with the 10w40 for now and maybe some 15w40 this summer (both OK for the '95 per the Haynes manual). I wasn't really worried about the 10w40, just wanted to run it by y'all. Thanks again.
Thanks, No significant leaks, just the usual dirty engine type seepage, but nothing drips or pools. Also engine does not consume abnormal amounts, probably less than a quart in 3000 miles at most. One neighbor, a Ford Motor Co engineer, suggested that a weak oil pump relief valve spring could be the culprit. Anyway, the 10w40 seems a reasonable compromise. Ideally I like 10w30, but in really hard summer driving the pressure can depress a couple more pounds or so below the 45. That may be a good reason to go with 15w in the summer as it has a better high sheer rate viscosity.
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