Oil Pressure

[3youngns]

I just picked up an 89 Bronco with a 351. Looks and runs great. EXCEPT. After the truck warms up, at idle the oil pressure gauge shows a drop and the check engine light comes on. If I put the truck in nuetral and bring the RPM's over 1000 the gauge shows that the pressure is normal.

I have been given a couple of different ideas on what could be the problem. From hardly expensive to hardly affordable. I would like to hear what you guys might think.

Thanks for your help,

3youngns

 

[Justshootme84]

hardly expensive would be a bad oil pressure sending unit. Hardly affordableand more likely is worn main bearings in the motor and/or a dying oil pump. You can still drive it if you don't hear any knocking in the engine, but i would keep a daily check on the oil, and make sure it's full. You might try one of the screens that fit on your oil filter. If it's trapping some metal filings, your motor is on it's last leg. Low oil pressure is a common problem in the Broncos, and the sending unit is not very accurate.

 

[highboy73]

when you change the oil put a bottle of lucas in it,the stuff is amazing

 

[Guest_3youngns]

Yea, those were the options that I was given. Try the Oil pressure sending unit first. Then it may be time to have the main bearings looked at. The guy I bought it from told me that he was told it could be the bearings. At least it is a second vehicle.

3youngns

 

[Jbronco]

I am having exact same problem as the gentleman said if my bronco drops below 1000 rpms after engine is warm my pressure goes to nothing i have been told change oil pump or pressure hoses but if any get this problem fixed please post reply Thanks

 

[Broncoholics]

Sounds like the idle needs to be raised slightly. In Dirve, its too low at idle to keep the pump going enough. I found bad connections on the oil sending until before. Ive also seen people use teflon tape to seal up the oil leaks on the treads. You need the metal threads of the sending unit to touch the block so its grounded.

Also use some 20/50 oil and perhaps some of that thick engine treatment stuff to help add oil pressure.

 

[Seabronc]

If you are in a hot climate try 10W40 or 10W50. I use 10W40 this time of year, if I use 10W30 I get the same indication.

Good luck,

 

[3youngns]

So far I have very minimal knocking. Sounds more like low grade gas than anything else. Since the first post I have changed the oil and the pressure sending unit. There was NO metal in the oil. The oil out of my street bike looked worse and its an '03. I went to a synthetic blend. I dont remember the weight but it is heavy. The pressure drops quicker now. A mechanic buddy sugested we start with the oil pump. I'll keep you updated.

 

[Shadow_D]

I had the same problem with my Bronco and it was the main bearings. I did have the motor replaced by the Ford dealer at a tune of $4000.00 :wacko:

I tried the oil pump and the heaver oil with no change but it was also knocking pretty good.

As far as the synthetic oil, it will not help you in this case as it will go through any openings you may have in the gaskets and it will make the knock worse.

I would suggest you baby that motor as much as possible and save your money for a new motor. You may even try getting a motor out of a junk yard and rebuild it yourself. Get a good manual that will give you all the info you need to do a rebuild, Haynes is a good choice as it has the wiring diagrams as well which will help when you swap the motor.

 

[Justshootme84]

I agree with SeaBronc on this one, try a slightly heavier oil ,but not a synthetic. I wpould also change oil about every 2000 miles to keep an eye out for any changes in consumption. You should use or lose no more than a quart/1000 mi. on a worn motor. You may not use near that much either if the rings and valve guides are still good.

My 84 Bronco went thru the same trend before I got my hands on it. I am good friends with the original owner, and he took great care of the motor. At 170,000 miles the pressure was dropping to nothing. He tried two sending units, but within a month of that it started knocking. Also tried a new oil pump, but the metal filings from the worn mains killed it within a week. The oil pickup tube also has a common problem of getting sludged up and clogged, which further starves the pump. ENd result was a new longblock kit, and a good deal for a used Bronco for me. I have had two other 351W motors die on me the same way.

 

[Broncoholics]

$4000 for a motor! @-)

 

[3youngns]

I've heard that this is a common problem. I have been checking the oil and it is not losing any. It just passed smog when I bought it. We'll see.

 

[JBronco]

I was just wondering how much of a pain changing the bearings is i know i have never done it before and if it is a pain to do would anyone know about how much it would cost for mechanic to do the job im pretty sure that is my problem i have no knocking sound but if i go below 1000 rpms with a warm engine my pressure drops to nothing thanks.

 

[Shadow_D]

Changing the bearings is fairly simple but it does require you to pull the motor.

If you are going to replace the bearings then I would suggest you go and rebuild the whole motor. If you do the bottom half only then you will most likely blow the top half.

You should get the block to a good machine shop to have it cleaned & checked along with the crank. You may also need to have the crank turned as long as it is still good.

You could also opt. for a short block (without heads) motor from Ford for around $1500.00 or a long block (with heads) for around $2000.00.

Going with the new motor will save you the time of doing the rebuild yourself and you can have your truck back in operation within a week.

If you do the rebuild yourself it could cost as much if not more than a motor from Ford depending on what parts you get. If you do the rebuild yourself you can spread the cost out for as long as you want meaning you buy the parts as you can afford them.

 

[Shadow_D]

I didn't have the tools or place to swap my motor so I had Ford do it for me. That's why it cost me $4000.00. Damn Labor :angry:

 

[Justshootme84]

THe longblock kit in my Bronco was installed at a local garage for about $950, paid by the previous owner. I spent the next several months repairing their shoddy work. WHile $4000 does seem rather costly, a good mechanic is worth the extra $$$ if you don't have the time to do the work.

Sometimes you can extend the life of a motor for a while by only rebuiling the bottom end (crank and bearings), but you prolly have just as much wear in the rings and pistons and the heads, valves, etc.

 

[Broncoholics]

I replaced my bearings by pulling the oil pan, intake manafold, exhaust and heads. I decided to put new rings on and hone it out with those little berry lookin things (rented) which just scuff up the side wall surfance for the new rings to seat properly. Seemed to work well and only took a weekend. If you have the tools, do it yourself and save some bucks and learn some stuff along the way. The biggest thing is make sure you know the torc specs on all the bolts. The rod bearings are only like 15-20lb. so you can over tighten them easy. Head bolts are 80-100 if I remember right. The book will tell ya...

 

[Guest_Ngapuhi]

I had exactly the same problem when I bought my 82XLT. Managed to fix the problem by leaving the motor in, dropping the sump and replacing the big ends and main bearings.

Oil pressure now on start up between 60 - 80. When warm it drops down to 40 - 60 which is great.

My mechanic who is a Ford fanatic and still owns his trusty 78 F100, recently purchased a brand new F250, tells me that the 351 motor has always had problems in the oil pressure department. He is the one who converted my truck from petrol to running dedicated LPG.

On each oil change my oil is like new, obviously due to having no carbon burning ie no petrol just pure Gas. The petrol we get out of a pump is like a lucky dip...thats why most of us run on LPG... it's a constant.

I have logged on and become a member... I think I've pushed the right buttons, I'm still new to the net and I'm better with a shovel than a keyboard..ha ha

 

[Ngapuhi]

My Mrs just showed me how to log in before I start. Sorry people.Live and learn a.