Well, I think my old 1997 Ford may be starting to lose compression. The truck runs well down the road, has plenty of power, starts the second you hit the key, and the mileage is as good or better than published specs for a new truck which isn’t great at 15-17. The truck came to me with 279,xxx miles and I have had it 12 years. Over the time I have owned it, the odometer never moved and I have no clue how long it has been that way. My guess is that the truck has well over 300,000 miles.
Anyway, here is what is going on. A few months ago I parked the truck in gear (it is a manual) and came out to the parking lot to find the truck had crept quite a distance across the lot. Luckily there were no cars in the way for it to run into. Now I shift it into low range if on a steep slope as that seems to keep it from moving. I also put a rock or other object under the tires if I think it needs that extra little stop.
I have noticed it doing this on my property as well. You can tell it is overcoming compression of cylinders over time. It will lurch forward until it overpowers the compression of the next cylinder, then it repeats. I haven’t done a compression test yet but it seems what I am seeing pretty much tells the story. The truck has always used a little oil but maybe a quart between changes. It is nothing crazy for a truck this old and hasn’t increased. The oil never looks all that terrible when I change it either.
What is the realistic life of these Ford 4.6 engines? I know they go a long time and I have always maintained it but everything eventually comes to an end. I am wondering if it is the valves which of course a wet compression test would confirm. It seems to be uniformly losing compression over all cylinders as well.
I am thinking with how it is running so well in this condition, I will just let it go until it presses the issue like burning a valve or whatever the end-stage of this will be. At that point I can decide to dump it or fix it.
I’d just use the parking brake and keep on driving. Just make sure it’s in good condition. If your truck has rear disc brakes, the park brake was marginal at best when it was brand new.
There’s a reason these engines were in such heavy use for fleet and commercial applications. Even when worn they still run well.
It was never engine compression that kept the truck from moving, it was engine friction. For compression to keep the truck from moving it would have required a completely airtight cylinder seal. That’s unlikely, there will always be some minimal air leak past the rings. You could always turn it over by hand, right? Same thing.
Compression would certainly have kept the engine from moving quickly when not running, but it obviously couldn’t keep a non-running engine still.
Still, it amounts to the same thing, you’ve lost some of the tension on the piston rings that cause the internal friction, but as long as the engine runs well, use the parking brake and drive it.
That’s what you should have been doing all along anyway.
No need to speculate, an engine compression test is a relatively simple shop job. Another idea, even easier, connect a vacuum gauge to the intake manifold. Does it hold pretty much steady in the 17-22 inch range at warm idle? If so, other than getting the parking brake working, nothing needs to be done.
My 50 year old Ford truck uses the 5L v8, has over 220K miles, passes the above intake manifold vacuum test. I haven’t measured the cylinder compression in past 30 years as there are no corresponding symptoms. A few years ago I thought I was having a compression problem, but it turned out the carb was leaking fuel into the intake manifold. Fixing the carb leak was all that was needed.
I think @cwatkin said his F-250 had rear drum brakes
I just checked and that setup seems to have 12" rear drums, which is probably a dual-servo setup, which often means a decent parking brake
Our fleet’s 1997 F-250 light duty 7-lug trucks had the 5.4-liter V-8 with rear disc brakes, with the parking brake in the hat . . . and the parking brakes were indeed very marginal, as @asemaster suggested
Yep! This is one with the drums so it is marginal at best. It works but not on a steep incline. I have wheel chocks now that I carry with me or use the nearest good sized rock for that purpose. This truck isn’t a daily driver but gets used around my property, taken to the river, camping, and hauling scrap or other materials that would beat up a truck.
Something else I do is put it in low range if parked where moving is a concern. That seems to help but I still back it up with something to block the wheels.
I will run a manifold vacuum test soon. I think these are common loaner tools but is this a tool that can be abused and be out of calibration?
I will also have the parking brake gone through next time it is in the shop for anything. I had that done not too many years ago but it leaves a lot to be desired. Again, I don’t think it was ever great.
I personally would just buy a decent vacuum gauge . . . it’ll probably be a kit with a few adapters . . . rather than borrow the tool
As far as being out of calibration, this is my non-scientific thinking . . . if the gauge reads exactly zero, not hooked up to anything, it’s probably still accurate
fyi . . .
I’ve only had one single vacuum gauge read incorrectly . . . because it was NOT pointing to zero when it wasn’t hooked up to anything . . . over the years, and the Snap-on vendor exchanged my gauge for a new one
Yes, definitely a real truck… I don’t worry about scratches with this one as it isn’t meant to be pretty and never was as long as I have had it. I have had loads of scrap metal, firewood, hay, brush, trash, etc. piled above the cab many times. Amazingly the manual transmission still shifts smoothly and the engine sounds fine. After sitting overnight there might be some lifter clatter for a minute or two on first start but that goes away and it is smooth after that.
It always get me how people have a close to $100K pickup all outfitted with the outdoor racks, gear, etc. and drive around a mud puddle. They are posers and should have bought a Corvette, Mustang, or something like that they way they treat their trucks.
Yes, but I’ve never noticed that problem myself. I’ve never tested mine for accuracy either though. They work basically the same as a tire pressure gauge. There must be a way to test their accuracy, but not sure how. A 100% vacuum should measure about 30 inches. A simple vacuum gauge can be purchased for less than $5. If you are buying one, I’d suggest buying the type that includes a hand-held vacuum pump. A good way to check for vacuum leaks.
Just use a hand vacuum pump to a vacuum gauge, pump a little to see if both gauges match…??..
If my tools weren’t so far away, I would run down and try that… lol
For some reason I don’t think it works like that, but I don’t remember why, if it doesn’t…
No nearby tools so can’t test, but I think that would work. At least to verify the two matched. Doesn’t guarantee they are accurate though. It seems like a person could use the eqn PV = nRT. Or P1/T1 = P2/T2. The pressure of a non-deformable sealed container P1 is atmospheric, 15 psi at room temp T1, then put it in the freezer, the amount of vacuum that develops , P2/P1 = T1/T2 could be calculated (I think) using the two temperatures. If if the calculated pressure dropped to 10 psi at the lower temp, the vacuum would be (10/15) * 30 inches. Of course there’s one major problem with this idea, whether the temperature gauge is correct? … lol
George, there are a few reasons I didn’t go to college to become an Engineer, and you just stumbled across one of them… I don’t have a freaking clue as to what you just said… I never said I was the smart one on here, ever!!..
