Oil burning 5.0, can it be diagnosed without tearing bottom end down?

dstang01 · Oct 30, 2009

So my 5.0 burns oil, about a quart every 600 miles. A little background, the car has 70,000 miles on it, compression is excellent on every cylinder, and one spark plug appeared oil fouled. It only seems to smoke on a hard accel or a downshift, this points to rings but it seems wierd that one plug is fouled and all the compression is so good. I was thinking maybe the valve seal on that cylinder, and was hoping to do an H/C/I.

Now this is a gamble, because if I set up my H/C/I and it still burns oil, Ill have to tear it down again to rebuild. I'd like to avoid rebuilding if I can, or tearing down the bottom end. Is there a way to spot bottom end issues looking into the bores when the heads are off (any give aways/hints to look for), or do you have to do a full tear down to diagnose?

final5-0 · Oct 30, 2009

If it were the seals ............

You'll have new ones when you go with new heads

Grady

dstang01 · Oct 30, 2009

final5-0 said:
If it were the seals ............

You'll have new ones when you go with new heads

Grady

That's exactly my point, I'm hoping I can kill 2 birds with one stone with my H/C/I, more power and stopping my oil issue That is... if valve seals are the problem

On the contrary, if rings are the problem, I'd hate to bolt up a nice new H/C/I only to still burn oil. Probably burn more oil too with the H/C/I than the stock setup due to higher cylinder pressures

Thats why I'm hoping theres a way to tell if its rings without pulling the motor.

Labora · Oct 30, 2009

I'm sure you've already checked. But make sure your PCV is good, it doesn't usually cause issues during decel but it can put undue pressure on things elsewhere.

Adam95GT · Oct 30, 2009

its dumb to risk it... if i were doing HCI on an oil burning engine it would be getting new rings no questions asked.

Chythar · Oct 30, 2009

I had the same dilemma with my old GT, but in my case the engine had a nice clanking noise going on. My mechanic said it was worn crank bearings, but I thought it was something in the valve train. So I tore off the top end to rebuild the heads. I got lucky; I decided to do things the right way and pulled the shortblock out to rebuild it as well. Turns out my crank bearings WERE worn - plenty of brass showing.

You're already partway there, best to rebuild the whole engine and know it's all good.

tderrick · Oct 30, 2009

You could run a wet / dry compression test on the cylinders ...

Compression test dry, then add some motor oil to the cylinders via plugs holes. Any improvement seen would imply rings. #'s the same, valve related....

dstang01 · Oct 30, 2009

tderrick said:
You could run a wet / dry compression test on the cylinders ...

Compression test dry, then add some motor oil to the cylinders via plugs holes. Any improvement seen would imply rings. #'s the same, valve related....

Correct me if Im wrong, but isn't a wet compression is used to rule out rings vs. valves, IF the dry compression is bad? In my case, all the cylinders fall between 150 and 155 on a dry. If it was rings, wouldn't the dry show it?

Check out my plugs too, the fouled one is from cylinder 3. Im not sure what this means, the cylinder had just as good compression as the others so I figure it MUST be valve related.

Adam95GT · Oct 30, 2009

dstang01 said:
Correct me if Im wrong, but isn't a wet compression is used to rule out rings vs. valves, IF the dry compression is bad? In my case, all the cylinders fall between 150 and 155 on a dry. If it was rings, wouldn't the dry show it?

Check out my plugs too, the fouled one is from cylinder 3. Im not sure what this means, the cylinder had just as good compression as the others so I figure it MUST be valve related.

No not if all the rings are equally bad. a wet test is the best way to tell... but like i said to be safe id just rering and rebearing the bottom end.

dstang01 · Oct 31, 2009

How hard of a job is it to re-ring the stock pistons? There are fairly inexpensive re-ring kits around, can you just drop the pan, unbolt the rods and slide the pistons out the top (with heads off) with the engine still in the car? Is it even worth doing this if I dont pull the engine and bore .030 over?

final5-0 · Oct 31, 2009

Wonder if you'd be money ahead with a junk yard explorer sb
that had low mileage

Grady

Adam95GT · Oct 31, 2009

final5-0 said:
Wonder if you'd be money ahead with a junk yard explorer sb
that had low mileage

Grady

and put a decent cam in it.... and be done..

TrueBlue95GT · Oct 31, 2009

dstang01 said:
How hard of a job is it to re-ring the stock pistons? There are fairly inexpensive re-ring kits around, can you just drop the pan, unbolt the rods and slide the pistons out the top (with heads off) with the engine still in the car? Is it even worth doing this if I dont pull the engine and bore .030 over?

I believe the stock rods won't fit out of the bores on the top. You'd have to push the rods as far as they will go to the top, take the pistons off and slide the rods out of the bottom....all while working around our bulky k member.

dstang01 · Nov 3, 2009

Awwww man, nothing's ever easy with stangs

At this point I'm wondering if its worth it to install the H/C/I for this winter's project with the short block as is, if it solves my problem then great

If not, I'll live with it for the year, then pull the motor and do a rebuild/ mild stroker next winter, the trickflow top end can be used for a 331/347 too (not to mention it's porting potential)

Honestly though, with excellent compression accross all 8 and that one fouled plug, I'm thinking it MUST be in the heads (unless I somehow cracked an oil ring in that cylinder, while the compression ring is in tact)

nmcgrawj · Nov 3, 2009

Sounds like u have your mind set.

Not sure how many options you will have up there for explorer motors...definitely a good option. I went this route for $500. Although....u could get a block with the same issues.

GDTrumbo · Nov 3, 2009

dstang01 said:
Correct me if Im wrong, but isn't a wet compression is used to rule out rings vs. valves, IF the dry compression is bad? In my case, all the cylinders fall between 150 and 155 on a dry. If it was rings, wouldn't the dry show it?

Check out my plugs too, the fouled one is from cylinder 3. Im not sure what this means, the cylinder had just as good compression as the others so I figure it MUST be valve related.

Have you checked your 150 to 155 psi readings against shop manual specs? If the 155 psi reading falls within spec and you have no cylinder down more that 10% of the others, your good. 70K is not a lot of miles by any means.

Try your test again. Remove All plugs and during each cyl. test, let it
turn over a good 6 or 7 times.

I think your probably seeing valve guide and seal wear.

GT

dstang01 · Nov 3, 2009

Thats what I'm thinking, just doesn't make sense to me to have ring issues yet. The owner before me was middle aged and had to get rid of the car for a minivan for his growing family, didn't seem like the kind of guy who beat the car to a pulp, but I guess you never know

The explorer thing is attractive, especially because you could replace the cam and springs and have a nice street motor. They aren't common at all up here in Canada though (my friend from washington has one, and I joke about swapping our engines when she's out of town ) plus you can't be sure the "new" engine is any more problem-free than the last without tearing it down, in which case you might as well just do so with your stock engine

I'll run a wet compression test and see if my pressures increase, and maybe a leakdown to be sure. Has anyone actually had a case of their oil rings going bad, but their compression rings still in tact?

79'293stang · Nov 3, 2009

Valve seals aren't hard, time consuming or expensive to change...Just install some new seals and if the smoking stops your in the green.

revhead347 · Nov 3, 2009

TrueBlue95GT said:
I believe the stock rods won't fit out of the bores on the top. You'd have to push the rods as far as they will go to the top, take the pistons off and slide the rods out of the bottom....all while working around our bulky k member.

Na, that's not true at all. You generally brake down the rod and piston with a press which you couldn't with it still in the block.

Kurt

revhead347 · Nov 3, 2009

dstang01 said:
Awwww man, nothing's ever easy with stangs

At this point I'm wondering if its worth it to install the H/C/I for this winter's project with the short block as is, if it solves my problem then great

If not, I'll live with it for the year, then pull the motor and do a rebuild/ mild stroker next winter, the trickflow top end can be used for a 331/347 too (not to mention it's porting potential)

Honestly though, with excellent compression accross all 8 and that one fouled plug, I'm thinking it MUST be in the heads (unless I somehow cracked an oil ring in that cylinder, while the compression ring is in tact)

Sounds like sound decision making. I think going with an HCI is a good choice. If it doesn't work, you can still re ring the block.

Kurt

Oil burning 5.0, can it be diagnosed without tearing bottom end down?

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