I bought a '76 F100 that I am in the process of fixing up. When I first considered buying it I just got it into my head that when you buy a 34 year old truck and intend to drive it fairly regularly you may as well rebuild the engine right off the bat. The truck came from out west and other than alot of surface rust, the body is in excellent shape so now that its down in humid, rainy south Alabama I want to get new primer and paint on it quick before the surface rust turns to cancer so that is the 1st priority with me.

Thing is, the 360 runs alot better than I could have hoped for buying it sight unseen. Cold, the oil pressure runs towards the middle of the gauge, hot, fairly low but still (barely) in the normal operating range. It runs cool in the few trips Ive had over 5-10 miles but when you shut it off it steams some and the gauge moves towards hot, going to flush the radiator, replace the t-stat and hoses. It needs a new carb, or a rebuild of the original and a good tune up but what other things could I do to determine if I should take it apart? If I do a compression check, what psi should I be looking for? Would a new oil pump boost the pressure or, if its worn mains causing the low psi, would it even be worth the trouble? I am working within a budget so I can either do the bodywork (and interior which is rough and all the little stuff that a 34 yo original truck needs, you can imagine) and wait on the engine or vice versa. Eventually, I'd like to do the 390 crank, rods and rebuild when circumstances permit.

 

I guess I would run a compression test first, just to get a feel for the engines internals. Don't know a good number for you there but I would go with anything over 90 is good. We will have to get more feedback from others in the forum.
As long as all the cylinders compression test numbers are similar to each other then you should be good for a while.
Maybe run a little heavier oil for now. Down south you should be able to run a 20w50.

new plugs and wires, and fix that carb and you might be pleasantly surprised at how well it runs.

That's my 2 cents.

Mark

 

My (very) limited understanding of the compression test is that it's not so much what the absolute number is as the pattern that the pressure gauge reports.

Again, I'm very new to this, but if she's bouncing wildly, you've probably got a bigger problem than if the average number is low.

There's a pretty good description of the behavior in the Haynes manual. (I got mine from LMC truck.) Worth the $20 I paid, for sure. If you want more information, you can do a "wet test".

Never tried any of this myself, but hope to soon... Oh, and please let us know what you find out!

 

"My (very) limited understanding of the compression test is that it's not so much what the absolute number is as the pattern that the pressure gauge reports."
Yep, as Poison Oil Racing mentioned, the ideal situation is if all numbers are very close. If you have one or more that are way different, you have problems.

"Again, I'm very new to this, but if she's bouncing wildly, you've probably got a bigger problem than if the average number is low."
I believe you're thinking about a vacuum gauge. A compression gauge usually pumps up to the highest reading for that cylinder and stays until you release the valve.

Here's a good video on how to check compression. A few things he forgets to mention is;
disable the ignition system,
hold throttle wide open
and make sure battery is fully charged.
YouTube - How To Check The Compression Of Your Engine

 

Since you plan to flush the cooling system, don't forget to set the heater temp to hot so the core gets flushed too. In fact, I pull the hoses and flush the core in both directions in case anything is lodged on the inlet side. Second, add a recirculating catch can to send the overflow back into the radiator. I use a Jeg's catch can ($19) and modified it to recirculate. Third, add a bottle of Redline Water Wetter (or similar product) to improve heat transfer. Lastly, switching to synthetic oil will also helps the engine run cooler.

I haven't done this yet but some gearheads have said to drain a gallon of coolant, refill the system with a gallon of white vinegar, run it for 10 minutes, then do the regular coolant flushing procedure. Vinegar is supposed to dissolve calcium and other minerals that tend to build up. Chemically, it makes sense.

Check out Survival Motorsports. They offer a kick-A stroker kit to change that 360 into a 445.

 

Go ahead and check the compression and see where you are at as others suggested. Complete the things you already said you were going to do to tune up the engine and also you might want to get some good manual gauges so see exactly what the engine is doing. I wouldn't rely on the stock gauges for overall engine performance especially when trying to make a decision on rebuilding your motor. If things come out well enough, than I'd just tune it and drive it.

 

Thanks Buck and all who have responded, I will take your advice. What do you guys think about the oil pressure though? A new pump is easy enough to install with the motor still in the truck but if that is not the reason for low pressure there is no sense in going to the trouble. I guess what I am asking is, is low oil pressure in an old engine more likely due to worn mains and internals or a worn out oil pump?