Compression on 2.8

[GKM007]

I have been leaking oil for some time out of many of my seals and decided today was the day to do a compression test.

1: 170
2: 165
3: 155
4: 165
5: 167
6: 165

Those number look decent all with 10% of each other which means my oil leakage should not be blowby? According to the Hayes book I need a minimum of 101 PSI, but does not say what top is.

On a side note 1/4/5/6 all pumped up quicker than 2/3. What might cause that valves?

I think I have proven that I do not have blowby with number like that? I guess after 280k its time to reseal the motor, its earned it.

I just wanted to run this thought by you guys before I buy the seal kit and start pulling this motor apart.

 

[wildbill23c]

Numbers look ok to me, I'm no compression expert, but I've owned several fords, they all leak oil somewhere, the 2.8L V6 well just worry if it isn't leaking something was always what I figured. Had every seal, gasket, etc. replaced in my 84 Ranger, it was leak free for a couple weeks and then it went right back to leaking in the same places it had leaked for years...I gave up and just added oil to it every month LOL.

 

[RonD]

Numbers look good but higher than I would expect

18 X Compression ratio = expected compression on test

2.8l has 8.7:1 compression ratio

18 x 8.7 = 156

But test depends on compression gauge and battery condition, faster crank speed = high compression numbers

I would think rings more than valves.
You could add a bit of oil to 2 and 3 and retest, if there is no delay after oil is added then it is the rings taking a few strokes to seat
If there is still a delay then you are right it is the valves.

 

[Angie]

I am no expert on these either, but in my 78 pinto with rebuilt motor and custom ground cam stock rest except for some head work. after 3 revs cold crank all 6 hit 180 on the compression tester. so your numbers look in spec if this helps any. maybe 5k miles on the build in 3 years. just goes out for shows and such.

 

[GKM007]

I was thinking as I drove to work this morning. 2 and 3 were the last I tested, might have just been cooling down at that point. By the time I figured out how to get the right angle on 3 I could touch the header. Might be closer to a cold number?

I might test 2 and 3 on their own while hot. I have to pick up a new plug on the way home, broke the ceramic getting it out. If they still act the same while hot I will have to try the oil method to rule out the rings. For the sake of time would it hurt to leave the rest of the plugs in and just take out 2 and 3? Might crank lower, but I could hook up my charger and set it to 60amp start to make up for the extra compression?

I have taken vacuum readings on the motor too. It sits at a steady 16, which is a tad low but not horrible either. I know the valve seals need to be changed as all plugs show a little oil, and it will smoke sometimes when I start it.

Order the gasket kit last night. $68 bucks for an entire gasket kit. Low price but a ton of labor!

I do have a brand new battery so it cranks nice and solid, it did get a touch slower by the time I got down to 2 and 3 maybe that could also account for lower number too.

This is the compression tester that I bought.
https://www.amazon.com/INNOVA-3615-Compression-Tester-Plus/dp/B001QJ9JRY/?tag=959media-20

 

[GKM007]

All cylinders but 2 and 3 reached max after about 3-4 strokes. 2 and 3 took 6-7 to reach max.

180 cold sounds really high based on the numbers Ron threw out, but I guess once you start doing cams and head work air volumes change a ton!

 

[RonD]

You did the compression test on warm engine........?

That would explain the higher numbers.
Use 19 instead of 18 for warm test compression expectation
19 x 8.7 = 165

Compression test is not about high numbers, it is about averages, and the difference between the average and highest and lowest numbers, the 10% thing.
And since compression gauges are usually not calibrated prior to every test and battery and start motor conditions vary, cold test will yield the same info as warm test, in my opinion cold test is often better because engine metal is not expanded so you may find larger difference in a cylinders psi when cold than when it is warm.


Yes, you can just remove one spark plug, disable the coil(spark) and dry test that 1 cylinder to get the slower crank speed number.
Then add oil, wet test, and see if pressure builds faster.

I think the 2.8l had solid lifters so probably not valve train issue.

The 4cyl pinto engines had higher compression ratios, so 170+ wouldn't be unusual, 180 average would mean some compression changes had been done, cam maybe shaved head most likely

 

[85_Ranger4x4]

I think the 2.8l had solid lifters so probably not valve train issue.

Unless not adjusted correctly.

 

[GKM007]

Everything I was reading on Google people were saying to do it after warm. But with that new number 19 x 8.7 = 165 puts me right were I am at, and I don't fluctuate more than 10%.

Time to do seals, lot of seals...

I am going to try the wet method when I get home though just cause I am curious, but internally I think I am looking good. Amazing that after 280k it's still a solid motor.

 

[GKM007]

In order to do my valve seals I will have to tear apart my valve train so I will get the chance to make sure that part is all good too.

 

[RonD]

The numbers 18 and 19 are not written in stone.
They come from the air pressure at sea level 15psi(14.7 really)
And then the mechanical compression added by the pistons motion, 3 when cold, 4 when warm.

If testing at 3,000ft above sea level the results will be lower because air pressure is lower.

So general numbers not precise by any measure, just a general idea of what to expect if you know the compression ratio for the engine being tested.


Yes, valves in 2 and 3 could be mis-adjusted but I don't think that would cause a delay in pressure building up, it would just stay the same.
Individual Hydraulic lifters could be effected by oil pressure and spring pressure when cranking, that was what the solid lifter comment was based on.

 

[AndyB.]

My 85 2.8 tests at 185 psi on all six.

When you pull the valve covers, check the baffle on the passenger side around the pcv valve, it can be car once off--make sure it's clear.

You'll likely find the valve guide deals riding on the valve stems and no longer seated on the guides. A leaky intake manifold gasket can also cause oil consumption.

A vacuum test would be helpful.