Took my newly acquired (it was free) 1990 F250 5.8L 351(103K orig miles) to my local mechanic to have at tune up and the oil pump replaced. Truck runs strong, no smoke an fires right up but has sat around alot. The previous owner removed all the emissions stuff ione of those things was bolted on front of engine and had pulley riding on serpentine belt. The previous owner stated that that now that the pulley is gone the serp belt rides toward the outside of fan pulley making it wear prematurely.

My mechanic was going through it and said he thinks the main crank is shot (since its connected to that same pulley) and that is was is causeing it to ride off center and not in fact that pulley from the now removed emissions part. His suggestion was not to put any $ into engine and not replace oil pump ( pressure would be fine at start up but once driving around would drop way low when at idle) and just replace oil often and drive as is till it finally goes. From there decide whether to rebuild or not.

The guy has been a great mechanic for me but just would like second opinion. His diagnosis seems kind of severe (or maybe I am in denial) just want to see what some of your thoughts are. I wont be driving this truck very ofter of very far (especially after that diagnosis) but it the main crank is not the issue I would rather replace oil pump and be on my way.

Thanks for the help!!!!

 

I've never heard of that before...Does the truck knock, groan, whine, or purr? When you said oil pressure is fine, is there a mechanical gauge installed to verify what oil pressure there is? The gen years of our trucks use a sender that basically registers oil pressure when the sender has 7 psi. It could be 25 psi and it will register anywhere between "N" and "L" of "NORMAL".

If you could get a pic of the belt and the pulley, we may even be able to help you decide what is causing it. Could be the pulley is incorrect, belt is incorrect, or pulley is incorrect..When people remove things and say, "Ahh, it's ok," doesn't mean it will be for very long.

Let us know your results.

EDIT: stated pulley was incorrect twice.

 

It sounds pretty smooth, no knocking or anything out of ordinary. The oil pressure is fine when running or a start up. Once it warms up and you come to stop/idle it will drop until you take off again. They hooked mechanical gauge to it to verify weak pressure. When I pick it up in the next day or so I will get more details on pressure readings etc and get a picture of belt/pulley. Thanks for the help

 

Glad to see they used a mech gauge on it. When you get the pics, maybe with a visual look, other members here can help you out further. Like I said I haven't heard of that happening, not saying anything is impossible, but would like to see the pics and other members will chime in.

Just for kicks, what oil filter is on the truck? If you look around here, you will find FRAM is unacceptable. Fram=Orange Can of Death. Stick with Wix, Motorcraft, Napa.

 

IMO i think the PO may have bent something causing the belt to ride wrong. If the tensioner is good and all pulleys are aligned correctly the serp belt has to track right. I suspect either the tensioner or the crank pully itself, not the crank.

 

i have seen people use a hammer to remove that pulley and bend it instead of using a pulley puller.
and you can try to runn trans fluid in the oil for a few hundred miles before you change the oil and see if that doesnt help out your oil pressure

 

I actually changed the oil last week and used a Fram filter. Guess that was bad move. Mechanic also mentioned that and I think he was changing it to Motorcraft. Once I pick up the truck I will get some more details on actual oil pressure and his thoughts on main engine crank. Hoping it is a just a bad pulley and an oil pump that needs replacement and not a bad crank.

 

Something I forgot to mention and based on ostrx250 reply got me to thinking. The water pump has been replaced on this truck in the not too distant pass and if I am not mistaken it runs off the main fan pulley too?? Maybe this could have been reinstalled incorrectly causing the belt to run off center? I may just be trying to convince myself the main crank is not shot but signs are pointing to more less threatening issue.

 

If they used the recommended pump and original pulley, it should be good.

 

Picked up rig from shop today. Switching out oil filter helps some but after warmed up will pressure gauge will stilldrop to floor when at idle. Mechanic says you can pull on main crank pulley and it will move in and out, indicating bearings etc. are shot. This movement is what is also causing the serpentine belt to wear much faster than normal. He does not reccomend changing out pump since it is putting money into an engine that may have less than 10k miles left on it and to save it for if/when I decide to replace motor.

Otherwise engine sounds and runs fine without a puff of smoke or any wierd nosies. So not sure if I should take his advice on oil pump or will changing out the pump give me more engine life, possibly as much as I need since this is typically used for trips to home improvement store and letting friends borrow to move stuff. Any thoughts or suggestions would be appreciated. Thanks!!!!

 

I'm starting to think your mechanic is right. There should be very little endplay in the crankshaft. Usually it's measured with a micrometer, not with your hands. Not a good sign. The oil pressure sounds like it's very low too. I wouldn't be surprised if you do need a rebuild in the near future.

 

being that the truck was free, pull the motor and put new main bearings in it and have the crank ground or replace with new, and then put your new oil pump in. new rod bearings would be a plus as well if you're replacing the crank

 

Yeah he has never steered me wrong with any of my other cars past or present. Superdutymj what do you estimate your fix would run me? Would I be better off with a complete rebuilt motor?

 

The cost is going to depend on a lot of factors. How much of the work are you going to do yourself? Are you just going to do enough to get it running right again or do you want a complete teardown and rebuild? Are you going to replace any parts that are worn and make it good as new?

I'd say anywhere from a couple hundred bucks up to $3k.

 

Would prefer to just get it running right without a complete tear down and rebuild. But with main bearings shot I may have no choice. This is beyond my mechanical ability so will have to pay the pros for this.