Compression check

[Insco2]

98 cherokee 4.0 bone stock.
185 k miles.
here my first entry. if in wrong location please feel free to move.
i bought a stock xj from a buddy for 450$
he had fought over heating problems.
he replaced the radiator water pump and thermostat.
it over heated on him 1 mile from the house and he nursed it home, parked it and went and bought a trailhawk.
with no knowledge of the damage done, i wanted to do a compression check to see where the engine was.
upon investigation i found a rubber freeze plug on the rear of the head out! i guess thats where all the coolant went.
what a fight but i managed to get a brass freeze plug somewhat into place with no leaks. loaded with coolant and ran some victory laps. no problems what so ever!
heres what the test proved.
engine warm.
all plugs removed.
throttle wide open.
cylinder
1: 100 psi *105 Psi after a teaspoon of oil to cylinder.
2: 135 psi
3: 130 psi
4: 142.5 psi
5: 120 psi
6: 150 psi
what are your takes?
i am going to run errends and smoke a pork roast will be back periodically today.
thanks all!

[4.3LXJ]

I would be a little concerned about #1. Check the cooling system for excess pressure. You might have a bad head gasket

[Insco2]

To be honest when I loaded the cooling system after installing the freeze plug, I noticed the upper hose was extremely hard to squeeze. I wouldnt assume that should be the case. From my understanding there should be very little pressure in the cooling system.

[4.3LXJ]

It won't go over 16 psi if the radiator cap is working. But that plug blown out may be a telltale sign of too much pressure

[Insco2]

Wouldn't the pressure be relieved out of the coolant overflow tank?

[4.3LXJ]

Yes, it would. But it would cause cooling issues also. Would tend to overheat easily due to gas pockets

[Charlie Foxtrot]

I like your approach. May I suggest doing a simplified cylinder leak down test while you have the plugs out. A worn valve, or mildly scored cylinder could account for the the low #1. Put some compressed air into the cylinder and see where it comes out. Also, how's the coolant look? Can you ask the prior owner about his coolant? If you hear reports of brown sludge, or serious discoloration, you may have combustion gasses getting into the coolant. Otherwise, its most likely just worn parts. good luck.

[Insco2]

I did add some oil to the cylinder and ran the test on #1 again, it did rise 5 psi.
Is a varied reading that far apart common. I agree with wearing parts. Just for sake of argument say it was valves and it did need a valve job. Would an increase in pressure across 5 cylinders say 30 psi be noticeable?

[Insco2]

I guess if I was going to do a head gasket, would putting a fresh head on it by worth the effort?

[4.3LXJ]

That is the right way to do it

[Mudderoy]

Wouldn't the pressure be relieved out of the coolant overflow tank?

If the cap is bad pressure could build.

[Charlie Foxtrot]

Varying pressures are normal, tho your spread is a little large, and #1 is kind of on the low side. There can be big differences between cold & hot engine pressures, so warm up the engine & recheck. If the numbers improve, it's just worn cyl/rings. Adding a little oil to low cylinder(s) and rotating the crank a few revolutions can help diagnose worn rings. A 5psi increase is not significant, in other words a small variance such as 5psi could arise just from slight variations in technique, not necessarily the addition of oil. Do the simple cylinder leakdown test - add compressed air into the cylinder at TDC (block the crank from rotating), listen to the exhaust (listen at the tail pipe), listen at the intake, open the rad cap & watch for bubbles, pull the dipstick & give it a listen, and pop off the oil fill cap in the valve cover and give a listen there. Bubbles at the rad cap is the kiss of death ( you will need to pull the head). Very small amounts of leakage at a valve can be normal and sometimes can be fixed by giving the valve stem a rap with a mallet - sometimes combustion deposits hold open or cock a valve. If that doesn't seal the valve, you can try checking the valve spring tension & maybe upping it a bit. Sounds of escaping air at the dipstick &/or valve cover indicates worn/broken rings &/or cylinder wear/scoring.

[Insco2]

If the cap is bad pressure could build.

I took the jeep out for a 10 mile ride last night it ran fine, although the upper radiator hose was so hard to squeeze by hand I'm wondering if the radiator cap might be bad. Should I be able to squeeze the hose manually when hot?