Dodge Grand Caravan 1999 - 3.8L low compression on one cylinder

[MaximumMini]

Looks like the head gasket is blown to the bolt hole, probably overheated then traded in when the issue from overheating revealed themselves.

I think I see what you are referring to.
My thought on that is that anytime theres a compromise to the headgasket allowing super heated gasses and actual flames to blow by the headgasket, you're going to have some kind of evidence of heat/burn damage be it ever so slight. I can't find any evidence of that so I felt it could not have been the headgasket?

Also, wouldn't a head bolt mostly prevent the escape of gasses due to no exit?

Wrong?

 

[MaximumMini]

So today so far I pulled the exhaust valve out and inspected it.

Dirty and good bit of carbon, probably due to not firing.
But no obvious burns, cracks or damage. Same with the seat and guide.

I still don't see anything significant enough to cause an 85% leak rate on the cylinder.

 

[MaximumMini]

What is the chance a malfunctioning LIFTER could cause this low compression (60psi, 85% leak down test result)?
Another thread on this forum seems to suggest if anything, a malfunctioning lifter will RAISE compression on a "engine off" cranking compression test.

https://bobistheoilguy.com/forums/threads/low-compression-most-likely-cause.44328/

 

[thastinger]

I think I see what you are referring to.
My thought on that is that anytime theres a compromise to the headgasket allowing super heated gasses and actual flames to blow by the headgasket, you're going to have some kind of evidence of heat/burn damage be it ever so slight. I can't find any evidence of that so I felt it could not have been the headgasket?

Also, wouldn't a head bolt mostly prevent the escape of gasses due to no exit?

Wrong?

Nah, I think you're correct but would be impossible to prove. I think it would be difficult for a head gasket alone to reflect a 100PSI compression loss...but a properly performed leak-down test would have reflected that loss if it were the gasket...that would be a big loss on a leak-down. You gaining 40PSI with oil in the chamber seems to have revealed stuck rings to me because the only way a single cylinder could lose that much would be stuck rings or a broken compression ring.

 

[MaximumMini]

The only thing I have yet to inspect is the Rings and the intake valve on this cylinder.
Beginning to feel I may find nothing wrong

 

[MaximumMini]

Nah, I think you're correct but would be impossible to prove. I think it would be difficult for a head gasket alone to reflect a 100PSI compression loss...but a properly performed leak-down test would have reflected that loss if it were the gasket...that would be a big loss on a leak-down. You gaining 40PSI with oil in the chamber seems to have revealed stuck rings to me because the only way a single cylinder could lose that much would be stuck rings or a broken compression ring.

Thanks Thastinger.
Next up I'm pulling that piston out of the block to check the rings.

Running out of places to find the source of the compression loss here.

 

[BornSlippy]

How did the spark plug look out of that hole?

 

[thastinger]

Thanks Thastinger.
Next up I'm pulling that piston out of the block to check the rings.

Running out of places to find the source of the compression loss here.

If you have a bore dial gauge, or can rent one, that would be good to run down the cylinder bore to see if it has become "egg-shaped" or has developed some significant "out of round condition" because a 15% leak down isn't bad on a 175K mass manufactured engine...but that leak-down test is performed at TDC so it only reflects the chamber and ring condition.

 

[MaximumMini]

How did the spark plug look out of that hole?

Like it had been misfiring but not wet or oily. Not too bad.

 

[MaximumMini]

If you have a bore dial gauge, or can rent one, that would be good to run down the cylinder bore to see if it has become "egg-shaped" or has developed some significant "out of round condition" because a 15% leak down isn't bad on a 175K mass manufactured engine...but that leak-down test is performed at TDC so it only reflects the chamber and ring condition.

I do and I will.

On this engine the leak was 85%
I was expecting to find a nice hole in the piston.

Just for the sake of knowledge......
If you remove the rocker shaft, what difference does it make where the piston is in the cylinder?

 

[MaximumMini]

Well guys, I THINK I finally found the problem.

Let me show you a few pictures. Tell me if this is it or not
No broken or stuck rings.....but broken RING LANDS between the rings. <scratches my head>
so will this cause catastrophic compression loss ? ;-)

What likely caused this?
No evidence of any damage to any heads, pistons or valves from detonation.

 

[BornSlippy]

Time for a Hellephant swap.

 

[BornSlippy]

My first thought after seeing that discolored valve is bad injector and it was running lean.

Here's a thread about a 3.8 in a Jeep;

C

Thread 'I think she was running a little lean.....'

Sep 29, 2020

2011 Jeep Wrangler 3.8L/42RLE with 131,xxx miles. Customer complaint......Misfire & a Squeaking noise.

*DTC P0303 (Misfire Cylinder #3), Using my Low Amp Clamp & Scope.....Verified one cylinder has low compression.
*Performed Leak Down test on Cylinder #3 at TDC with Bank 1 Rocker Shaft removed, 75% leak down.....With no air escaping the Intake or Exhaust valves.
*Removed Bank 1 Cylinder Head (Which is quite easy) & found the Piston had a broken Crown/Ring Land, Galled the Cylinder wall, And had been VERY hot (Has a charcoaled look to it)
*Flowed all 6 injectors & found #3 to be severely...

• clinebarger
• Replies: 49
• Forum: Mechanical/Maintenance Forum

• 

 

[MaximumMini]

My first thought after seeing that discolored valve is bad injector and it was running lean.

Here's a thread about a 3.8 in a Jeep;

C

Thread 'I think she was running a little lean.....'

Sep 29, 2020

2011 Jeep Wrangler 3.8L/42RLE with 131,xxx miles. Customer complaint......Misfire & a Squeaking noise.

*DTC P0303 (Misfire Cylinder #3), Using my Low Amp Clamp & Scope.....Verified one cylinder has low compression.
*Performed Leak Down test on Cylinder #3 at TDC with Bank 1 Rocker Shaft removed, 75% leak down.....With no air escaping the Intake or Exhaust valves.
*Removed Bank 1 Cylinder Head (Which is quite easy) & found the Piston had a broken Crown/Ring Land, Galled the Cylinder wall, And had been VERY hot (Has a charcoaled look to it)
*Flowed all 6 injectors & found #3 to be severely...

• clinebarger
• Replies: 49
• Forum: Mechanical/Maintenance Forum

• 

Good read. Thanks!
Gives me something to consider as probable cause

 

[Exhaustgases]

Well guys, I THINK I finally found the problem.

Let me show you a few pictures. Tell me if this is it or not
No broken or stuck rings.....but broken RING LANDS between the rings. <scratches my head>
so will this cause catastrophic compression loss ? ;-)

What likely caused this?
No evidence of any damage to any heads, pistons or valves from detonation.
View attachment 274020

What is the line and color difference on the land between the 1'st and 2nd rings that is almost inline from the bottom of the wrist pin?

Yeah interesting having that chunk gone. Rings too tight? Over heating?

Your overhaul parts list is getting more expensive.

 

[MaximumMini]

What is the line and color difference on the land between the 1'st and 2nd rings that is almost inline from the bottom of the wrist pin?

The color change is right at the crack.

Yeah interesting having that chunk gone. Rings too tight? Over heating?

No chunk missing. Everything is there and in place. Just cracked. Fortunately.

Your overhaul parts list is getting more expensive.

Ya know, until today that's exactly what I thought.
But it seems that's the only cylinder with a problem so I'm gonna assume that injector was not working properly and leaned out that cylinder just enough to cause the ring land to break. I'll replace that injector, install a new piston, rings and all the seals AlI can and should be back in business in a few days.
I'm actually more optimistic now because the bearings were in Pristine condition, like new.

 

[meep]

I think @thastinger is on it.

I rebuilt a Chevy 283 years ago. It had a fairly notable ridge on it, about 8 sheets of college ruled notebook paper thick, and the cylinder walls were glassy smooth. But smoothness doesn’t count when they are simply polished surfaces but no longer dimensioned right. It had to be bored out 40 over because the wear was around 32 at the worst. The naked eye won’t catch it nor will fingers, but measuring N-S, E-W at the top, bottom and middle began to tell a story. You could put new rings on it and maybe see some improvement, but hard to say how much.

I agree that a valve or head problem might make more sense here, since it’s just one. You’re deep enough in in a short period of time that you could have that head redone, put new rings on it and try it? Clearly head work will improve it, perhaps enough to be happy with it?

Or go ahead and pull it for a rebuild or even mild build! Probably can’t stroke it more than it is, and the bottom ends dont handle boost, but maybe a slightly more interesting cam?

 

[MaximumMini]

I think @thastinger is on it.

I rebuilt a Chevy 283 years ago. It had a fairly notable ridge on it, about 8 sheets of college ruled notebook paper thick, and the cylinder walls were glassy smooth. But smoothness doesn’t count when they are simply polished surfaces but no longer dimensioned right. It had to be bored out 40 over because the wear was around 32 at the worst. The naked eye won’t catch it nor will fingers, but measuring N-S, E-W at the top, bottom and middle began to tell a story. You could put new rings on it and maybe see some improvement, but hard to say how much.

I agree that a valve or head problem might make more sense here, since it’s just one. You’re deep enough in in a short period of time that you could have that head redone, put new rings on it and try it? Clearly head work will improve it, perhaps enough to be happy with it?

Or go ahead and pull it for a rebuild or even mild build! Probably can’t stroke it more than it is, and the bottom ends dont handle boost, but maybe a slightly more interesting cam?

Thanks.
Tomorrow I'll get dimensions to see if the cylinder is out of round.
I have inside mics for that.

 

[Exhaustgases]

Yeah pics are pics. Sure looks like a chunk out of that land between oil ring and 2nd compression ring just above the boss area for the wrist pin.
Optical illusion ?

 

[Donald]

Hi, first post here.

I have a newly acquired 1999 Dodge Grand Caravan 3.8L

If I didn't know cars and engines well, I would probably keep driving this vehicle since it pulls hard and feels darn near normal when driving and idling.
But there is always someone who knows more or has had similar experience.
Problem is, it is throwing an occasional P0302 (misfire cyl 2) code and bucks very slightly at idle when in gear.

removed rocker arm, no obvious damage to rocker pedestals, springs or rocker arms. looks good.
Did a compression test and got 60psi (very low). Adjacent cylinder 190psi (very good)
Did a leak down test and it was inconclusive. No clear indication of where the leak was. But it was large (85%)
I was really dissappointed in the leak down test. I had expected clear evidence of the source.
I did notice a small amount of air coming out of the dipstick tube when I removed the dipstick. But it seemed like too little to be significant.

Poured a bit of oil into the suspect cylinder and compression went from 60psi to 100psi.
Would that be enough for you to conclude a problem with the rings?
Tomorrow I'm going to look inside the cylinder with a borescope and see if I see cylinder wall damage. If I do, game over. engine comes out for a rebuild.
If no damage, I'll probably take the head off and inspect the head and head gasket.

I've started adding Marvel Mystery Oil to the cylinder yesterday to let it soak a few days and see if the rings might be stuck by carbon buildup from cheap gas etc. I've read many accounts of it unsticking stuck rings and restoring compression.

Any suggestions or comments welcomed.
Thanks

Forget MMO. It's a mystery anyone buys the stuff anymore.

If you are going to try and soak the piston use a real solvent like Seafoam. You will need to change the oil after the soak and before starting the engine. But most people use a soak to help with crud around the oil control ring not the compression rings.