Hey guys well since i restored my 1978 f-250 with a 351M and a 4speed in it. I blew my clutch out of it last saturday of november. It was orignal clutch anyways tho. But we instlled new clutch and everything and took motor out to do this and put a new rearmain seal, mains, and oilpan gasket and valvecover gaskets in the motor. We cleaned everything and made sure nutting was in the motro when we put it back together and isntalled it. We also changed the oil and oilfilter in it (who wouldn't?) I have been driving it for little whle now and over the weekend friday night it was fine then saturday it was fine but sunday comming up over the ridge i glanced down and oilpressure guage is peged at the low end. I had no oilpressure. (quickly pulled over checked everythign out nuttign smeeled hot or anything and motor not makign any sounds or nockign or anything) Ok started it back up drive for 3more miles (to where iw as going then parked it and it got cooled off there). Left there started it up and the needle went up to the low side of the N in NORMAL. So i drive it home (like 3 more miles) and it dotn have any loss of power or anything. What do you guys reccomend I do? I was thinkign about changing the oilpressure sendign unit in the truck to see if it is going bad or not. Please let me know if you have any idea wuts going on .
thanks,
Jimmy

 

Don't freak

Even though the 351M had a bad oiling system ....sometimes little pieces of gasket or engine crud can get stuck in the sending unit and this makes for low pressure readings.
Just remove the SU and try and clean it out.

While it's out, hook up a mechanical gauge and get a positive reading
I suggest to mount a mechanical oil pressure gauge in the same spot as the sending unit for a genuine pressure reading.
You can use a T-line to install this.

 

Maybe a bad Oil Filter. New Oil Filter are known to be defective.

The best check of oil pressure is to test it with an oil pressure tester.

 

the oilfilter was a ford motorcraft one. I dont know it was running fine all along then bang it droped like a rock....

 

when you installed new bearings what size did you use?????????? it is possible the engine has been rebuilt with a .020 grind on the crank by now. you may have installed STD. bearings instead.

 

no the engine is standard and nothing done to it before (we know because the truck been with us since new) and my dad had installed standard some tiem ago but while it was apart we saw that they were little thin so we installed new ones..

 

did you platiguage the new bearings or just throw them in?

 

I run two oil pressure guages, the stock one and an aftermaket one. I like knowing for sure. Too much bearing gap will drop your pressure. Some oil filters are lower restriction and will drop your pressure. Then there's always the possibility the sending unit was damaged, wire was damaged, or it's a loose fit.

 

Well guys i put a pressure guage in my truck (screwed it right into the intake) and im getting 80psi when its cold and once its warmed up and ideling at 750rpm its at 35psi. and as soon as you touh the throttle once warmed up itll go up to 75psi... So as for that I bought a new oilpressure sending unit for my truck (tryed to clean the old one then it wouldn't work at all) so i just go ta new one to install.
thanks,
Jimmy