I ran a quart of Marvel Mystery Oil in my engine last oil change, and it made my engine MUCH smoother and noticeably quieter. However, I think the engine flush clogged up my oil pickup screen. Any ideas on how to unplug it before I go and drop the oil pan? I already tried replacing the oil sending unit but that is not the cause of the very low oil pressure in my engine.

 

I would go ahead and drop the pan. It might take too long for any kind of solvent to work before your engine is damaged.

 

Its a Marvel it still runs....although I wonder just what it did clean up.

 

I suspect the Marvel Mystery Oil flushed deposits that were reducing flow in worn cam, main,& rod bearings, oil passages etc. Increasing the flow reduced the pressure. Try increasing the weight of the oil you use (maybe to 20W-50), if it increases the pressure then you'll have a pretty good idea that it's not the screen clogged. Reducing the operating temp via a lower temperature thermostat may also increase the oil pressure (higher temp = larger bearing clearances = more flow = lower pressure and vice versa). Maybe the oil pump is worn, too.

 

Lariat, can you be more specific? How low is the pressure and how much change does that represent?

 

If Piffery1 is correct...you should be hearing the main bearing knock when you first start up...it would sound something like an instance when you just change your oil and you start it up for the first time, only it will keep on knocking lightly, but get louder as you increase rpm. I also think that increasing the oil pressure would help and suggest a product called Lucas Oil. Its an oil additive for racing engines and would increase the oil pressure quite a lot. Your friendly auto parts dealer should stock it. I tried the Marvel Oil Mystery years ago, and it did the same thing to me....and then changed the oil and increased the oil pressure...problem solved.

 

Okay, here is the long version:

My '85 F-150 (rebuilt 60K miles ago) had a "tick" sound in the motor. Several people recommended I substitute one quart of Marvel Mystery Oil and run it for about 500 miles or so. The Marvel Mystery Oil worked fantastic and made my engine run smooth as silk. I changed my oil, and all is well. My truck ran GREAT, oil pressure was where is should be, and engine was quiet, no leaks at all. About 3K miles later, I noticed my oil pressure would register low every now and then. It would often start off great, drop lower, and stay low, but sometimes it would come back. The last few times I started it, it stayed low so I shut it off. When I say low, I mean between the "N" and "O" in the "NORMAL" band when it was previously between the "M" and "A". I changed the oil again, and the oil still looked good, and I found nothing suspicious in the oil filter. I changed the oil sending unit, but that is not the problem. The engine still sounds good and smooth with no knocking sounds at all, but the oil pressure is still WAY lower than normal.

 

I think you ought to install a mechanical oil pressure gauge and see where you really are before tearing into the engine. If the factory gauge is in the "normal" range the engine is probably getting enough oil. The gauge is more of a relative indication than an actual gauge. There's no guaranty of liniarity or anything else.

 

I have an interesting thing with mine, my oil pressure gauge is not accurate... and it's that way because of "under dash" temperatures. the heat under the dash is enough to give false reading on the gauge. I'm not too sure if it's all that common of a problem where you are, but here, in Canada, this problem USUALLY arises when people start turning on the heat. Just some food for thought is all.

 

Had this on a 351w in a '88 van. Was screen on pickup clogged from valve seals. I'd drop the pan and clean it. I know its a pain but really the only solution. I pulled mine and rebuilt it since was over 100k miles and had been run on low oil pressure for awhile before I found out. (Employee was driving it)

 

On my '83 w/460 "N" in "Normal" is ~12 psi and needle just slightly to right of straight up is 65 psi (oil pump relief valve setting) as measured on a good quality gauge. If you get a mechanical gauge don't get an "El Cheapo", I've had one that took 14 psi to move off Zero although it was ok @ 30 psi. P.S., You can usually tell the good gauges, they come with copper tubing rather than the plastic stuff.

 

Having observed such a noticable change in pressure, I agree that you should confirm the readings. But your own assessment that the pickup screen may be blocked is not unreasonable. The only reason to suspect the gauge is the fluctuations. But until you confirm the reading it would be wise to keep the load and the rpms down as a precaution. Look for any fluctuations in the temp gauge too, if they both act peculiar at the same time it could be the little voltage regulator on the instrument cluster circuit.

 

Thanks guys. The temperature gauge is working fine; only the oil pressure is reading way lower than normal. I talked to a mechanic today, and he told me that a good engine should not develop any sludge to block the pickup screen, regardless of age, and that unless the oil pump is malfunctioning, I probably have a problem in the engine. Does this sound correct? If the problem is indeed a clogged pickup screen or oil pump, will replacing the oil pump with a "high volume" oil pump offer any advantages?

 

A high volume pump is not necessary unless your engine is used at very high rpm and/or very heavy load. It consumes power to run the hd pump.

If you find that your screen is blocked, since the pressure was ok before, cleaning it may be all you need. But if you take the trouble to drop the pan, you might be more comfortable changing the pump anyway. And you would be well advised to plastigauge a few bearing so you get a good idea about how the lower end is holding up and insure that there has been no damage due to the low pressure situation.

 

I'd put a good mechanical gauge on it and measure pressure at 1000, 2000 & 3000 rpm. If you get at least 10 psi per 1000 rpm (at normal operating temp) i.e., 20 psi @ 2000 you're probably ok for a while. If not, I'd pull engine and check rod and main bearings clearances. High volume pumps are mainly for racing engines built with larger clearances although you can use one on a worn engine to get higher pressures. But, I'd fix the problem instead of treating the symptom.