Hi,

I have a 1990 F-250 - 5.8L V-8. The oil pressure drops to nothing at low rpms when the engine is warmed up. I already replaced the oil pressure sending unit just to make sure it wasn't that.

Anyway, so now I suppose I'll need to replace the oil pump.

I notice in the manual, it says to remove the intake manifold, disconnect the radiator, etc before jacking up the engine for clearance to the oil pan. Is this all neccessary (particularly removing the intake manifold seems excessive)? I can understand the radiator disconnect... but the intake manifold? Why?

I thought I would get some of that engine flush stuff from autozone, and flush the engine prior to removing the oil pan. Has anyone used this stuff? Will it cause more problems than it solves?

Thanks,
Daniel

 

Hey Dgpruitt,

Before you do this, I believe that 1990 trucks also have the ghost oil pressure gauge. That is, the gauge is just a calibrated idiot light. The giveaway is the sending unit size. Small = ghost gauge. Large (about 1"diameter, and 2" long) = real gauge. If the ghost is your setup, check your pressure with a machanical gauge. Oil pumps are a lot of work, hate to see you go through it, and find that all is well. Also, these gauges are NOTORIOUSLY finnicky. My 95 flops all over the place, and it's a ghost gauge.

If however, you DO need to do the oil pump, no you don't have to remove the upper intake. You can raise the engine enough to get the pan out. The pump must be removed and dropped into the pan to get the two of them out, and installation must be done with the pan sitting on the crossmember. Not a BAD job, but kinda cumbesome. Just be SURE to take your new oil pump apart and FLUSH it before you install it. I also pack some vaseline into mine to aid as a primer after flushing them. Also, spend the extra money and get a 1 piece pan gasket. You'll be glad you did.

Hope this helps.

 

Thanks for the info re: pressure switch. This is what my oil pressure sending unit looks like:



This required a 1 1/16" socket...

I already have the new oil pump, I bought a melling high volume pump. It looks to be the same size as the regular pump, so I hope there won't be any need to modify the oil pan for clearance.

Also, I already bought the multi-part oil pan gasket... maybe I'll go back and get the single piece one if that one works better/easier to install.

When you say, "flush" the oil pump prior to installation, do you mean to just run some oil through the mechanism (and then pack with vasoline)?

Thanks again,
Daniel

 

dgpruitt,

That is the sending unit from the GHOST oil pressure gauge that I
mentioned in my first post. Save yourself a LOT of work (potentially). Go and get a mechanical gauge. Hook it up where the sending unit above currently is, and drive for a day or two. Watch your oil pressure. You may not have any engine trouble, and your gauge wiring is kaputt. The setup that you have is notorious for being troublesome. Mine is all over the place. Remember, that gauge is just a calibrated idiot light, and that sending unit above is just a switch. Just like for an idiot light.

However, if you DO in fact have problems (do you hear your lifters clacking? any bearing knocks?), then what I mean by flushing the pump is this:

Take the four bolts out of the bottom of the new pump. Take the rotors out of the pump next. Then spray some degreaser throughout the pump, and blow it out with compressed air. Just in case there is any metal chips left over from the machining process, I do this. Put the rotors back in. Pack the spaces between the rotors with Vaseline. Reinstall the cover, then reinstall the pump.

Hope this helps.

 

I also saw that you're buying a high volume oil pump. I wouldn't use that. Stick with a standard oil pump, and you'll be fine (assuming that you need a pump that is).

 

I do get some rattle/clacking on a hard accelleration - lower gear, high rpms (sounds like lifter noise, almost like a diesel engine).

No knocks or rattles occur during the low oil pressure readings, however.

I'll get a mechanical gauge, and see what's happening with the oil pressure.

Thanks,
Daniel

 

OK. I put in a mechanical oil pressure gauge.

Cold, the pressure starts at 25 @ idle. After warming up, the pressure settles to about 6 @ idle.

After seeing this. I changed the oil, and put in straight 40W -- no change in oil pressure behavior.

So what's next. The new oil pump install? I checked the ford dealership, they quoted me $575 for parts/labor. Ouch! I suppose I'll try it myself.

Daniel

 

Wait a second. How many miles are on this motor? With those kind of pressure readings, it sounds more like your motor's shot. What happens is the bearings wear down and can't hold oil pressure the way they used to, and you get lower readings.

My motor runs over 50 lbs at cold idle, and 25 at hot idle.

 

why not use high volume pump? i am in the process of replacing my oil pump in my 94 300 six. i was leaning to the regular pump but some have said get high volume without really stating reason.

my oil pickup had a lot of crap in it when i took it apart.

thanks

 

Here's my take on high volume oil pumps. Take it for what it's worth. On older high mileage motors, if you pump the oil faster than it can get back down to the pan due to sludge buildup, etc..., you'll starve of oil. I've seen this before. Also, I've seen where guys wind their motors up, then at the high end, they lose pressure. They lose pressure for the same reason mentioned above. They suck the sump dry. Our motors in our trucks run for miles and miles with the stock oil pumps. A lot of engineering and time goes into developing these items. If you have low oil pressure, and put a higher capacity pump in, you're throwing good money after bad. Chances are that your bearing clearances are excessive also, and you're ready for a rebuild anyway. I've never used a high volume pump, and have never had any problems(knock wood ). That's my take on the issue. I'm sure that others will differ with me, and that's OK.

By the way Dgpruitt, at least now you KNOW that you've got an oil pressure issue. I also agree with ANDYM. How many miles are on your motor, and were they high miles? Let us know, and we'll help you as we are able to.

 

The truck has 86,000 miles. I bought it used, about six months ago. I've put maybe 2000 miles on it, mostly driving around town doing chores. I'm hoping it will be a good work truck. It gets used primarily to hawl construction materials from Home Depot (~50 miles round trip), and to take trash to the dump.

I don't know how this truck has been used in the past, although it had been fitted for a gooseneck trailer hitch, so maybe it towed a horse trailer or something similar.

An update on the pressure behavior: At a cold startup (first start of the day), the pressure starts at 55psi. It drops as the engine temperature rises, and at idle it eventually gets to 0psi. At this point, when you step on the gas, the pressure rises to about 10-12psi.

 

Er, that should be haul.

 

86,000 is pretty low miles on a 90. Maybe add 100,000 to that? My 90 with the 5.8 was doing exactly the same thing and after a couple of weeks, it started thumping and eventually knocking. I found a good size pile of bearing in the pan when I swapped the new motor in. This happened at 150,000 on mine.

 

According to the title and the title history (from carfax.com), this is the actual mileage.


The oil pressure problem has been present for as long as I have owned the truck (6+ months). But the engine doesn't have any bad knocks, except for some valve or lifter noise on heavy accelerations.

I'm inclined to try the oil pump replacement, see if there's any metal in the oil pan. If that doesn't work, then I suppose the engine will need a rebuild. I'll probably put that off for as long as I can since I can't afford to put that much dough into the truck right now.

The engine seems to have decent power, I was able to tow a bobcat with the front-end loader and backhoe attachment from Santa Fe to Pojoaque (uphill both ways ) without too much trouble.

 

my dads van is an 86 econoline 150 w/ 351w and it only has 70,000 some miles on it, I know this cause he bought it new when I was a kid. Anyways, it needs to have the oil pump replaced. We had a new oil pump screen replaced but they didn't put in a new pump while they was in there so now we are paying for it again... the lifters peck a lot at 60-65 but if you keep it easy maybe 50-55 at the most it'll be fine. We've tried changing the oil numerous times with 10w30 trying to do quick oil changes to clean out whats in there. We took it on a trip awhile back and stopped at jiffylube to get a quick oil change and they put in 5w30 because thats what the "manufacturer" reccommends. I seriously dought that in 1986 ford or any other car maker reccommended 5w30. Right now it has 10w30 mobil oil and since he put in 2 bottles of stp oil treatment the oil pressure is great, and the engine doesn't peck anymore. Next time I change it I'm gonna go with a 20w50 instead of using the oil treatment. Yes we know the oil pump still needs to be replaced but at least this is a good quick fix.