Sort of a Newbie. Compression test.

[Ronw435]

Hi all, not new to the forum but was wondering about a compression test question. I have a 1986 Ford F250 6.9 NA. Mileage unknown. I use the truck to plow a mile and a half road in the Northern New Mexico mountains. The truck starts great when plugged in in the winter down to +10 degrees. (Haven't tried it any colder as the need didn't arise. ) I thought that I would give it some maintenance as the brakes were a little soft and goes to the floor under constant pressure. Going to install a new master cylinder, new rear brakes as the seal had gone bad on the floater and fouled the shoes.

My question is that the truck runs good.... a little light on power... but runs good. A little blue smoke when you first start it but after it has run a while it clears up mostly. No bubbles in the radiator and the oil cap will sit on the spout while idling with out lifting it up when loose. I just performed a compression test and all cylinders were 200 to 220. This I believe is quite low for a diesel. The truck was cold....45 degrees...and the tester i have does leak a little at the fitting. I am checking it through the glow plug holes and the tester I bought was for a IDI Ford/ IH. there were two fittings that were the correct size threads but it did not fit like I would have liked. My question is would the compression be acceptable if the fittings fit well. I use the truck to mainly plow our road and I have to use low range to get up the hills. The road is a mile and a half long. The truck runs well on the road but like everyone says its not a speed demon but since it is mainly a plow truck I don't want to put 5 grand into rebuilding the engine.

I have not done a leak down test yet but was wondering if re-ring would help me out and be worth the work?

Thanks
Ron

 

[lotzagoodstuff]

I'd get your fittings sorted out and do a proper compression and leak down test to try to verify what you really have, but in my opinion, if it starts well, I wouldn't be too worried about it. While you have the glow plugs out, I'd check all of them and replace as needed. You shouldn't have to plug it in at +10 F, your glow plugs should do the job with regards to cold starting. Nothing wrong with plugging it in (instant heat is nice in the winter), but if you ever take it someplace where you don't have access to plug it in, you'll be happy you got a good glow plug circuit.

Lastly, if you really just plow with it, I'd try to put a load on it and run it hard until you see some elevated temps. It is possible that your rings are carboned up and a good workout sometimes helps. I also really like AutoRX for cleaning a carboned up high mileage IDI.

By the way: you are spot on about about the "not a speed demon" comment. No matter what you do, when you get a normally aspirated IDI up in elevation, they do struggle to make power.

Good luck whatever path you choose to pursue.

 

[BrandonMag]

I have not done a leak down test yet but was wondering if re-ring would help me out and be worth the work?

NO.

X2 on what lotzagoodstuff recommended.

Tearing the engine out of the engine bay, mounting it on a stand, taking the heads off and knocking the pistons out of the jugs is WAY TOO MUCH work for an old IDI that you're using to only plow a road. If it runs well enough to do what you need don't mess with it.

 

[Ronw435]

Thanks guys for the replies

I will take your advice and get it good and warm with some diesel clean in it to try to free up possible stuck rings.

Thanks this blog rocks.

 

[Big Bart]

Some other thoughts.

There is no stated range of compression from ford. Just that no two cylinders are off more than 20%. (Based on that you are good.) As stated if it runs good and does the job, keep going, you likely will not cause harm running it till it has issues. As a guage my truck has 400PSI on most cylinders. But I would not be concerned at 300 PSI if they all were in range. 200 PSI sounds low, but if its starting and running decent I would guess your gauge is bad. But untill you see issues needing attention like sever oil burning, lots of smoke all the time, blow by, etc., etc. Just keep running!

1) Also not sure how you did the compression test. But here is what I would suggest -
a) Hook up a battery charger. Helps keep the starter running equally as strong on each cylinder test.
b) Remove all the glow plugs out of the gate.
c) Use a starter switch and hook to the starter relay on the fender. (So you can turn over the engine at the engine bay. Since the key is not in the ignition and in the run position the truck cannot start.
d) Count 5 compression strokes and stop. Do so for all 8 cylinders. I watch the frist one to get a guage of a potential issue (Like a valve or rings.) but it is after 5 compression strokes you should count the reading.

2) Perhaps borrow or buy a better compression set.(Like the OTC brand.) If your glow plug adaptor does not fit right or your gauge is cheeper chicken, it may not be holding all the pressure or reading right. You may have 300psi but it reads 200psi. Or you have 350 PSI but much of it is leaking past the threads on your glow plug adaptor.

3) I would also suggest your check your timing. May help with power, easier starting (Can make a big difference.), and smoking. Some recent posts (Also many older ones.) on how to do so. Tools to do so are $170-300. As stated in many posts, running down to your local truck shop ends up in someone tunning by ear because they do not have the tool and don't want to buy one. Well that is guessing not tuning! So if someone says they can, confirm they have the right tool for the job.

Happy plowing!

 

[Ronw435]

Thanks for the tip Brad.

I did test the compression through the glow plug holes. I had all the gp,s out when i did the test and two good batteries.

I am going to put a new thermostat in it(Motorcraft) and try to work it enough to get it good and warm. Would taking it up in the mountains on the highway and pull it up the big hills in 2nd gear be the way to work it? Its a C6. 3.55 gears. I really don't have anything to really load it except for a box full of wood.

What would be a good solution to put in the cylinders to try and free up the rings , if that is part of my problem?

I was told the truck was used as a plow truck for a church for the last several years. Maybe it has not been run enough to get things loosened up?? I have not put it on the road for the last three years as I only plow our mountain road which is private.