Help with Compression Test Results
08-03-2015, 06:02 PM
#1
Senior Member
Thread Starter
Help with Compression Test Results
These numbers aren't good, but as far as I can tell not horrible. The engine doesn't "burn" oil but does have a leak (1 quart every 2 months). No unusual smoke coming out of exhaust. When doing a vacuum test, pressure test, and block test all came out ok. Vacuum is on the low side, but within normal range during idle. Engine has at least 180k on it, but it could very well be 280k, or 380k.
#1: 120
#2: 120
#3: 120
#4: 120
#5: 150
#6: 100
#7: 100
#8: 100
This is after adding oil in 6-7-8 just to see what would happen. It increased a little bit but not much.
What would you guys do with this truck? A complete rebuild isn't in the near future, I think. Do you think the compression would drop rapidly, or do you think I can drive it around (2k-3k miles/year) until it gives out or I can rebuild the motor?
-Pat
#1: 120
#2: 120
#3: 120
#4: 120
#5: 150
#6: 100
#7: 100
#8: 100
This is after adding oil in 6-7-8 just to see what would happen. It increased a little bit but not much.
What would you guys do with this truck? A complete rebuild isn't in the near future, I think. Do you think the compression would drop rapidly, or do you think I can drive it around (2k-3k miles/year) until it gives out or I can rebuild the motor?
-Pat
08-03-2015, 06:25 PM
#2
Not horrible. It should last like that for a long time yet.
#5 could be so much higher due to carbon buildup. Have a good look at the plug for that one, it may not be firing as well as it should.
On an original motor after 25 years, those aren't bad numbers.
A big part of the loss from original will be the valves. Adding some oil for a wet test like you did seals the rings, so now you're testing the valves.
Had it jumped up substantially after adding a few drops of oil (wet test) that would indicate a serious problem with the rings.
Since it didn't, that tells you that the rings are pretty good still, and any leakage is mostly valves - which is to be expected, they're not going to seal perfectly forever.
Most people's thought at this point is to throw rebuilt heads on and boost up the compression, but that's not always the best idea.
If you redo just the valves you throw a bunch of extra pressure at the bottom end of a 25 year old motor and usually take out the bearings.
A good case of if it ain't broke, leave it alone.
A can of seafoam engine treatment, half in the oil and half in the gas tank will help clean up some of the gunk and should make it last a little better.
It's far from a freshly rebuilt motor though, so obviously mashing your right foot to the floor is not a very good idea. Drive her easy, she'll probably just keep on turning for years yet.
#5 could be so much higher due to carbon buildup. Have a good look at the plug for that one, it may not be firing as well as it should.
On an original motor after 25 years, those aren't bad numbers.
A big part of the loss from original will be the valves. Adding some oil for a wet test like you did seals the rings, so now you're testing the valves.
Had it jumped up substantially after adding a few drops of oil (wet test) that would indicate a serious problem with the rings.
Since it didn't, that tells you that the rings are pretty good still, and any leakage is mostly valves - which is to be expected, they're not going to seal perfectly forever.
Most people's thought at this point is to throw rebuilt heads on and boost up the compression, but that's not always the best idea.
If you redo just the valves you throw a bunch of extra pressure at the bottom end of a 25 year old motor and usually take out the bearings.
A good case of if it ain't broke, leave it alone.
A can of seafoam engine treatment, half in the oil and half in the gas tank will help clean up some of the gunk and should make it last a little better.
It's far from a freshly rebuilt motor though, so obviously mashing your right foot to the floor is not a very good idea. Drive her easy, she'll probably just keep on turning for years yet.
08-03-2015, 07:51 PM
#4
Like Chris said there not terrible numbers. Ya u dnt want to run the hell out of it . It's 25 years old but I think It will be fine for awhile . Doing sum things to clean out the motor alittle will help just alittle like sea foam
08-03-2015, 08:21 PM
#5
Senior Member
Thread Starter
I already own the truck, and will give a little history behind it.
I've posted a few other questions about repairing the car. I originally bought it to haul around pinball machines. I'm literally going to only be driving it for probably an estimate of 2k-3k per year. Shortly after getting the truck, I just fell in love with it, and found myself just taking drives down the highway for the heck of it.
I then started getting excited about the truck, and this is my first experience with repairing my own car. I created a blog about what I've done to it, and my trials and tribulations. I thought of making the engine perform better, increase mpg, and horsepower, etc. I had made some plans for it.
Thinking I put the cart ahead of the horse, I thought I'd start doing the major checks to see how worn out the engine really was. I have a running hot / coolant loss issue I'm currently working with, so have done a couple of the big tests already with that. I finally thought what the heck, I'll do the compression test. If it comes back good, I'll make it my baby and really start working on it (changing out exhaust, adding some more performance goodies to it).
Since it came back as it did, I started thinking that maybe I should sell the truck and get something else with a fresher motor (92-96) or should I just keep this one, and when it gives out to then really look into doing something crazy, like a 408 stroker.
This is really my first experience of having to deal with this, so just wasn't sure what to think of it.
So you guys would keep it still, don't go nuts with it, but give it small repairs until it gives out and needs a rebuild?
-Pat
I've posted a few other questions about repairing the car. I originally bought it to haul around pinball machines. I'm literally going to only be driving it for probably an estimate of 2k-3k per year. Shortly after getting the truck, I just fell in love with it, and found myself just taking drives down the highway for the heck of it.
I then started getting excited about the truck, and this is my first experience with repairing my own car. I created a blog about what I've done to it, and my trials and tribulations. I thought of making the engine perform better, increase mpg, and horsepower, etc. I had made some plans for it.
Thinking I put the cart ahead of the horse, I thought I'd start doing the major checks to see how worn out the engine really was. I have a running hot / coolant loss issue I'm currently working with, so have done a couple of the big tests already with that. I finally thought what the heck, I'll do the compression test. If it comes back good, I'll make it my baby and really start working on it (changing out exhaust, adding some more performance goodies to it).
Since it came back as it did, I started thinking that maybe I should sell the truck and get something else with a fresher motor (92-96) or should I just keep this one, and when it gives out to then really look into doing something crazy, like a 408 stroker.
This is really my first experience of having to deal with this, so just wasn't sure what to think of it.
So you guys would keep it still, don't go nuts with it, but give it small repairs until it gives out and needs a rebuild?
-Pat
08-04-2015, 07:12 AM
#7
Senior Member
As Chris said. You can expand your knowledge and resources during this time and track down the coolant loss/hot running which may be a head gasket. If this gets bothersome enough and you pull a head some decisions might be made for you. Have fun!
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08-04-2015, 09:12 AM
#8
Senior Member
Thread Starter
Well, I took the truck to a buddy of mine with a mechanic's shop. I just wanted to make sure my block test and compression test were done correctly.
When removing each plug in cylinder 6-7-8, water was found in the cylinder and blew out a bit when the engine was cranked (I don't know why I didn't see this before). He's saying it's a cracked head gasket, which probably leads to the losing coolant / running hot as well.
So I guess now, do I cut my losses and just sell / junk the truck and buy another, repair the head gasket, or put a fresh rebuilt engine in it?
It sounds like the only "sure" thing is putting a new crate in it? Fixing the head gasket could cause the bottom end to go bad with the extra compression, (however oil pressure is nice and strong). A used / rebuilt engine, well heck you have no idea what you're going to get there.
-Pat
When removing each plug in cylinder 6-7-8, water was found in the cylinder and blew out a bit when the engine was cranked (I don't know why I didn't see this before). He's saying it's a cracked head gasket, which probably leads to the losing coolant / running hot as well.
So I guess now, do I cut my losses and just sell / junk the truck and buy another, repair the head gasket, or put a fresh rebuilt engine in it?
It sounds like the only "sure" thing is putting a new crate in it? Fixing the head gasket could cause the bottom end to go bad with the extra compression, (however oil pressure is nice and strong). A used / rebuilt engine, well heck you have no idea what you're going to get there.
-Pat
08-04-2015, 01:32 PM
#9
Senior Member
You could rebuild it yourself? Learn, experience, tales to tell, if you have time and inclination. Sounds like you might have some resources available at you buddy's shop.
I'm sure you could find a quality engine rebuilder in you area, your friend would have some ideas. Since it's not your daily driver you still have time on your side.
I'm sure you could find a quality engine rebuilder in you area, your friend would have some ideas. Since it's not your daily driver you still have time on your side.
08-04-2015, 08:34 PM
#10
If the trucks in good shape I'd put a new motor in it . Try to stay awAy from a used motor unless u can here it run first and it dnt have a **** load of miles. Like u said a crate motor could be a good idea probly wat Id do.