Compression Test Results - Need advice

[edog1973]

So I did a compression test on the 460 in my Holiday Rambler yesterday.  The motor seems to run strong with no major issues.  However we are planning a long trip next summer.  I want to find and repair as many issues as possible before we leave. 


When I pulled the plugs they all looked normal grayish tan color.  Except one had a deposit between the electrodes.  The valve covers where the PCV valve and oil filler come out have quite a bit of oil on them (PCV valve rattles, so I assume it's OK).  I was thinking this may indicate excessive blow by.   


Here are the test results:


Cylinder 1 - 120
Cylinder 2 - 110
Cylinder 3 - 120
Cylinder 4 - 130
Cylinder 5 - 125
Cylinder 6 - 110
Cylinder 7 - 100
Cylinder 8 - 120


I ran the compression test with the engine cold. (There is not much room getting to a couple of those plug holes and I'd like to avoid charred skin on a hot manifold)  From what I've read the lowest needs to be 75% of the highest which is almost exactly where where she is at.  Should I call these results good and move on?  Should I test again after warming it up?  Any advice is welcome.

[Oz]

Any1?

[Froggy1936]

You can call it OK and just move on OR No1  You did not give us the current mileage Nor when the oil was last changed  Fresh non diluded oil is important, If it is not new ( less than 100 miles) Change it Replace the spark plugs with a step hotter Drive it a short distance 10 mi or so Let it cool enough to prevent burning yourself Remove and inspect plugs Indexing them with cly removed from THen With ign killed (remove a wire from the coil)  Block the throttle wide open and remove the air filter Check compression mentally  noteing first needle position crank eng to max reading and record  After all 8 squirt 1 squirt of oil into ea cly and spin engine 5 sec Then recheck all cly compression writeing the readings below first set of readings , Any major difference in 1st and 2nd reading means a ring /piston defect Refering to your chart and the first set of readings determines your decision  Now your sorry you asked  eh  Frank

[Rickf1985]

Frank went into the really long version, I don't know why he suggested hotter plugs? But the compression test should be done with the throttle held open the entire time. From what I see those readings especially on a cold engine raise no flags at all to me. The oil at the valve and oil fill is normal and just a result of many years of minor leakage around the seals. If you are worried about blowby get it hot and then with it idling take the oil fill off and see how much if any blowby comes out. Should ideally be zero but if it actually does have over a hundred on it then a little will be fine. Froem what you said about the plugs I don't thing the rings are bad and it does not sound like the valve seals or guides are bad either.

[edog1973]

OK so earlier today, before anyone responded, I went ahead and ran the test again warmed up.  Not by Frank's standards, I just ran it in the driveway for 15 minutes until the temp gauge was at 190 for a few minutes.  I don't know the age of the oil it, but it's not black.  I'd say it does not have a lot of miles on it, but could easily be a year or two old from talking to the PO. I did have the throttle held wide open while performing both tests. I forgot to mention in the first post that the engine has 138K on it.  I think.  The odometer is at 38K and I have Internet VIN report that shows it was at 74K in 1992.  Plus the PO said it had about 100K when he got it 10 years ago. So the numbers from the second test are... Drum roll please....


Cylinder 1 - 130
Cylinder 2 - 135
Cylinder 3 - 135
Cylinder 4 - 150
Cylinder 5 - 145
Cylinder 6 - 130
Cylinder 7 - 120
Cylinder 8 - 140


OK, the drum roll may not have been necessary. Each cylinder went up roughly 20 pound from cold to warm.  I didn't do the second part of adding oil to each cylinder and testing again.  If that's critical please let me know.  At this point I'm leaning toward saying "I did my due diligence, and I think she has better that a 50% chance of surviving a 10K mile trip without needing an engine rebuild."


If you disagree please let me know.  And thank you to Froggy and Rick for the replies.  It's much appreciated. 

[MotorPro]

Drive it !!!

[Rickf1985]

Drive it. With 138 thousand on it and being in a motor home it has had heavy duty use so those numbers tell me it was very well taken care of. I would definitely get an oil sample from the transmission and send it in to a place like Blackstone and have it analyzed. That will tell you the general condition of the transmission and it is a hell of a lot more accurate than the local transmission shop who is going to immediately want to throw in a rebuilt tranny. What I would do is to call or go online and get a kit from Blackstone (or whomever you prefer, that is who I use) and then drop the trans pan after warming it up and get a sample of the oil and change the filter and put in new oil. Judging from the engine condition I am going to guess the transmission has also been well taken care of but if it is an overdrive tranny then Fords are known for failures in the low 100 thousand mile range. Better to address on your time than on a trip.

[edog1973]

Yep, I think we're just going to drive it. If we do run into issues we'll deal with it.  But I'm a lot more confident about its condition now.


Thank you for transmission testing recommendation. I just ordered the kit.  Transmission condition was next on my list.

[Froggy1936]

Sounds dependable, Change that oil & filter 6000 mi max or 1 year recommended !  Frank The hotter plug was due to deposit on 1 and the greyish color  solid brown is perfect !

[edog1973]

Just a quick follow up:  I took Rick's advice and had the tranny fluid checked out by Blackstone labs.  For the most part it looks like it's in good shape.  There are a few readings out of line, but they can be caused by old oil.  Here is the notes from the report they sent me:

"Well, mostly this transmission is in good shape. And the two things that are out of line are not necessarily problems. Aluminum can show wear at the torque converter or oil pump, or it could just be oxides off the case, maybe if this Rambler was sitting for a while before you bought it. Insolubles are the solids that are present and they could be from keeping the oil in place too long, or maybe something else caused them to form. The bottom line is, let's see how it looks after an oil change. We suggest resampling in 10K miles to monitor."

I have to say I was impressed with the service.

[Rickf1985]

Good to hear, I am going to venture a guess that the transmission is a C6? Three speed? If it is a four speed it is an AOD but they were not quite as heavy duty and unlikely it would be put behind a motor home. A C6 is a good solid transmission and the fact that after 100,00 it is showing a good oil analysis show the vehicle was not beat on and probably was driven easily with slow starts from lights and such. You got a keeper!

[CapnDirk]

Hey guys.  I see the oils sample kit is free, how much did the test cost?


Thanks

[edog1973]

It was $28 to have the analysis done.  Not cheap, but with what we all end up dropping into these money pits not unreasonable.

[legomybago]

A friend of mine had doubts on this type of oil testing that he was paying for on his dump truck. So he took a sample of the nastiest old (known) blown engine oil That had been setting out in an old bucket and sent it to caterpillar.......guess what? The test came back with excellent results!! They said his oil was perfect!!! That was the last time he paid for an oil analysis. I'm sure this is an isolated event, but you never know.....

[Rickf1985]

We are not talking about Cat here, they want the engine to go so they get to rebuild it. We are talking about an independent lab that has no financial interest in the end result of testing. They live by their test result reputation. I had a sample run through the spectrograph at the college I worked at at the same time I sent a sample to them and although their testing is much more thorough the tests on the spectrometer were spot on. These people have absolutely nothing to gain by lying and everything to lose.

[legomybago]

Good point Rick....

[CapnDirk]

All reputation aside, I was surprised at what I think is cheap insurance to know your trans. is going south.


If you are using good engine oil and normal time span changes there is not much you can do about the engine (you can usually smell the dipstick and tell that gas is in there).  The transmission is usually the neglected part.  You could pretty much ask anyone with over 100K on their vehicle if the trans filter and fluid have been changed and the answer would be no, or I don't know.


You never know if the PO(s) ever did anything to the trans.  Now that I know the cost of this, I'm going to test the trans fluid.

[Rickf1985]

You have to remember that a transmission is a sealed unit so there are no outside contaminates coming in that need to be filtered out. The only thing that needs to be filtered out in a transmission is the normal wear of the clutches. The oil itself will last a lifetime as long as it is never overheated. The filter will last as long as the clutches. Chances are pretty good that on a motor home the oil has been overheated a time or two, just by how much and how long. If it is still red and does not smell burnt then you are in good shape. It is perfectly normal to drop a transmission pan and find the magnet covered with black fuzz and residue in the bottom of the pan, this is normal clutch wear and does not indicate a bad transmission. This is where oil analysis comes in, to let you know just what is in the oil so you can make an informed decision on what to do.