The oil pressure on my 327/300 seems to have taken a noticeable increase following an oil change. It's now running at 70-80 psi nearly all the time except at idle when its about 60. (Car runs fine.) The manual says 35-40 at normal operating temperature. I changed the filter element but I did use straight 40 weight to try to quiet down a noisy tappet. I've had low pressure problems with cars in the past but not high. What are the ramifications and what else should I do other than go back to a lower weight oil?
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Re: Midyear - High Oil Pressure
I'm surprised straight 40 weight could drive the oil pressure that high, but I've never tried it. I assume you're estimating the max pressure based on how far the needle goes past the highest reading on a gage, which should be 60. There are a variety of additive products on the market that have a very heavy detergent additive dose (Bardahl, Rislone, etc.) Read some labels and pick one that you thing might work best to free a sticky lifter. Then I'd suggest changing back to your previous grade of oil with the additive to see if the lifter will free-up. I can see where 40 weight might produce excessive oil pressure on a cold start in sub-freezing weather, but it should drop down to a more normal level once the engine is fully warmed up, so there might be something else at work here.
I run straight 30 weight API CF-4 heavy duty diesel engine oil in my old cars. The CF-4 blends have a much higher dose of dispersant, detergent, anti-wear, and anti-corrosion additives, but their combustion by-products are not friendly to catalytic converters, which is why the concentrations of these critical additives have been *reduced* over the years in spark ignition engine oils. The CF-4 blends are also available in 15W-40 blends for colder climates. (I live in Southern California.)
Duke -
Re: Midyear - High Oil Pressure
Dave, I've got a similar problem with my 66 327/300. I had the engine rebuilt last year and my oil gauge needle is way past 60.The only modification I had was hardened seats. I can't help you with an answer, but only share the problem.I don't know if my siyuation is normal. Frustrating,isn't it!Comment
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Re: Midyear - High Oil Pressure
Hi David:
I used to run Valvolene 50 weight in my Big Blocks in the sixties and the result was the same. If this pressure bothers you, assuming it is a correct evaluation on your part, ( 80 psi ), simply change back to your regular oil. The jury is still out on the effects of high oil pressure as there was a thread a month ago regarding increased oil pressures and no consensus was reached but the guideline is 10 psi per 1000 rpm.
jerryComment
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Re: Midyear - High Oil Pressure
David-----
I suspect that there may be two factors at work here. First, your use of 40 wt engine oil increased your oil pressure to some degree. Second, the lack of linearity which these old analog gauges often exhibited is making a small real increase in pressure seem like a much larger one. If all that you did was change the oil from, say, 30 wt or 10w-30 to 40 wt, it should not have had such a dramatic effect on REAL oil pressure.
What I'd suggest is to temporarily install a high quality test gauge of 0-100 PSI range in your system. Use as large of diameter flexible line as you can (e.g. 1/4" ID) to connect the oil gauge to the engine. Install a "T" fitting at the engine so that you can maintain your existing oil gauge in the circuit. Then, "calibrate" your existing guage to the test gauge. You won't be able to perform the calibration in any sort of permanent way, but you'll know what the gauge marks REALLY MEAN with respect to oil pressure.In Appreciation of John HinckleyComment
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