Bad bad news on my ride...

It overheated, so I replaced the thermostat and got that all squared away, no more overheat problems, at least not after an hour of idle. When I took it out for a test spin, the first 5 minutes were fine, and then I steadily lost all my oil pressure. Was sitting on the "L" by the time I got it back into my driveway.

I'm not sure what caused the pressure loss when I was under way. Pressure was fine through some revs and an hour + of idle. Now I've picked up a very noticeable knock. I have no oil in my coolant, it wasn't noticeably burning through it, I'm at a loss to explain the pressure drop.

Also, does anyone have any experience with replacing the rod bearings to fix knock? What is the threshold for this working effectively or needing to swap in a new engine? Im not opposed to the idea of picking up another good 351w or 302 but that's a much larger project than I am equipped for. Will a mechanic be able to tell me reliably which option to pursue or is it a total crapshoot?

Thanks in advance!!

 

Total crapshoot. Most mechanics will just tell you to replace the engine with another one.

However, if you have time to rebuild it, and you haven't scored anything past what can be considered as fixable, you can totally fix your current engine.

 

In order to rebuild you will need to determine what the problem is. But, you should also figure out if a rebuild is reasonable before embarking on that expense. In other words, if you are losing oil pressure and/or have a knock then you know you have bearing problems. But, it may not be worthwhile spending money on the engine if the rings have lost their grip and/or the heads are warped or the head gasket has let go - all of which can easily happen due to overheating.

To figure that out you need to do a leak-down test as a compression test will not answer the above questions. But, a leak-down test will answer the questions and it isn't that difficult. You can Google it, but here's a link to a good description of how to both build and use one: Leak-Down Tester.

If the leak-down test tells you that you have good heads, head gaskets, valves, and piston rings then you can move on to the bearings. But, if the test says one or more of those things I listed are bad then you have to decide if you want to go to the expense of doing the bearings and repairing whatever the test said is wrong.

If it is just the bearings, which I personally doubt, then you can pull the mounts loose, pull the exhaust loose, remove the fan shroud, and raise the front of the engine and pull the pan. Use Plastigauge to determine the rod and main bearing clearances by pulling each one of the caps, one at a time and inserting a small piece of Plastigauge, re-installing the cap, torquing it down, and then pulling it back off and reading the width of the Plastigauge via the scale on the package. Compare that reading with what it says in your shop manual - and I strongly recommend not starting on something like this w/o a manual. However, you will also have to inspect the condition of the crankshaft's bearing surfaces while you have the caps off, and any scoring will require removal and turning down.

Also, you will not know the condition of the cam bearings when doing this. Normally they are ok, but they are also the last thing oiled so doing all of the other work w/o pulling the cam to check the bearings is a gamble.

Good luck!

 

Reminds me of my daughters toyota. Lost oil pressure followed by a knock, knock, knock. Had great compression still and started and ran pretty good still.

2 new rods and a new crank later, she was back up and running. Well until she ran it out of oil again....it's in the junk yard now

 

now as to why your truck lost oil pressure...could be lots of reasons. If it just went away then maybe something with your pump or the drive to the pump. If it slowly went away then the bearing may have been the original failure. You could have wiped or spun a bearing and it slowly ate itslef. Once the bearing(s) is gone, then you have no back pressure in your oil system and pressure goes away. You're basically just dumping all your oil/pressure in to the now empty cavity that used to be a bearing and back into your oil pan.
So the bad bearing may have caused the oil pressure to go...not the oil pressure casuing the bearing to go. Hard to say until you get in there and look

 

I've gone ahead and decided to just go ahead and swap the engine. I have a mechanic friend who will cut me a good deal on the labor of doing so (he also has access to a hoist ) so that resolves that problem, kinda.

This brings me to my next total newb question... What engine? Will any carbeurated 302 or 351w between 68 and 85 bolt in? To make it easy on my guy, I'd like to have to do as little re-arranging in the engine bay as possible. What engines would be a direct bolt-in swap?

Details: 84 F250 4x4 with 110000 miles, 4spd manual tranny and original 351w.

Thanks for all the input guys, super helpful!

 

I would stick with the 351w...you will have better low end torque over the 302. Try to keep it in the same era as the one you have. I have read that some of the earlier (mid 70's and earlier) had different size heads so that might be an exhaust alignment issue. Also in the 80's they added the provisions for emissions equipment.
So if you stick to one in the early 80's, you'll have the best chance of all your accessories fitting correctly.

 

I agree - go with a 351W. Yes, a 302 will bolt in, but they went EFI long before the 351's did, and EFI would require several changes including a computer, electric fuel pumps, etc. If you can find a 351W from 84 thru 86 it will be carbureted and won't have a computer as they are the HO variety. The earlier 351W's were also carb'd, but many of them would have originally had a computer (EEC-IV) and computer-controlled ignition (DS-III). If you find one of those you'll have to put the distributor and ignition-control module on from your existing engine - and use the DS-II wiring harness.

And, the 300/4.9L six will bolt to the tranny. However, you will need different engine perches, a different radiator, and different exhaust - and maybe more.

 

I thought the 351W 2V carb'd models didn't begin the Feedback Carb/EEC-III stuff until 1984, prior to that would have been DSII.

Chief would know for sure.

 

EEC-III Duraspark-III

EEC-IV went with the TFI-IV modules.

EEC-III, Duraspark-III was mostly a California thing.

 

Well, the '82 Explorer I had was sold in KS and had DS-III and a computer. I understood it to be EEC-IV, but could have been mistaken, but I know for sure the ignition was DS-III. And, I was told the carb was feedback, but never saw it.

And, the brown '82 behind the shop was said to have been "computerized" so the PO put a points-style distributor in, disconnected the computer, and installed a different 2150 carb. I can't confirm that it was DS-III, but he said it wouldn't run properly w/o changing out the dizzy, so I can only assume.

 

Thanks for all the help! I found another 351w with good compression out of an 85 F150 with the same tranny set up as my 84. Pick up some new mount and main bolts and should have it swapped over this weekend. fingers crossed that it won't turn into a nightmare and is a simple straight-across swap

 

Glad you found it. Should be a straightforward swap.