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how to tell when blowby is more than the ccv problem?

C

cjben

NAXJA Forum User
Location
Illinois
My 1992 xj 4.0 is using one quart of oil about every 250 miles,more than that if i put a lot of highway miles on it. It has 180,000 miles on it. I did a compression test about 6 months ago,and all cylinders were between 130-140 psi and the plugs weren't oil covered,they looked normal. i am planning on doing some bolt on upgrades to sqeeze a few more ponies out of it before long,but I don't want to do it if the engine is toast. I know these engines are good for a lot of miles,but my xj shows signs of previous owner neglect. so the question is: Is there a way to tell if the blowby is the ccv problem,or something more serious? I have noticed the engine smokes on start up,but from what i can tell it doesn't smoke while i am driving it,and it still seems to have quite a bit of power. . thanks for the help,Ben
 
cjben said:
My 1992 xj 4.0 is using one quart of oil about every 250 miles,more than that if i put a lot of highway miles on it. It has 180,000 miles on it. I did a compression test about 6 months ago,and all cylinders were between 130-140 psi and the plugs weren't oil covered,they looked normal. i am planning on doing some bolt on upgrades to sqeeze a few more ponies out of it before long,but I don't want to do it if the engine is toast. I know these engines are good for a lot of miles,but my xj shows signs of previous owner neglect. so the question is: Is there a way to tell if the blowby is the ccv problem,or something more serious? I have noticed the engine smokes on start up,but from what i can tell it doesn't smoke while i am driving it,and it still seems to have quite a bit of power. . thanks for the help,Ben
Click to expand...
I think the only way would be to replace the CCV fittings and tubes to see if it keeps doing it.
 
The Orifice in the CCV system can clog, I would "think" that would throw the system way out of whack. Have you tried cleaning out the orifice with a pipe cleaner? As well, check over the tubes and fittings and make sure there is no vacuum leak?
 
also pull the valve cover off and clean the underside off it and the baffles under the holes for the ccv lines/grommets.

clean off any sludge from the rocker arms and valve springs and make sure the passage for the oil are not clogged.
 
A leakdown test will tell you an awful lot about the insides of your cyliners, and how well the valves are seating.
 
Since the compression numbers were normal on all cylinders, that virtually rules out any serious piston ring blowby and any valve problem.
If there are no external oil leaks to account for the oil loss, the likelihood is that your engine has worn valve stem oil seals. These would allow oil to leak past the valve guides from the crankcase into the intake ports especially under high vacuum situations (deceleration, closure of throttle).
Blue/gray smoke from the tailpipe in these situations would be a telltale sign.
 
dr dyno,it is smoking blue from the tailpipe at start up,but i would think it should be smoking the whole time it is running to be burning a quart every 250 miles. thanks for the ideas.
 
I had bad valve stem seals in a V6 in an old mini-van I had. It didn't make any smoke, unless I sat at idle, the longer I sat, the worse the blue smoke cloud would be when I pulled away. Like Dr. Dyno said, high vacuum circumstances sucks the oil thru the valve stems into the motor, and it can suck a lot of oil. The next time you have to wait at a light, watch out your rear view mirror for blue smoke coming up, especially when you pull out of the stop, any oil sucked in will burn then when you rev up the motor.

OR, your CCV system is messed up and the oil is puking up into the air filter.
 
What weight and type/brand oil are you using?

What kind of oil pressure do you have?

Do you have any external leaks, like the oil filter adapter or real seal?

So far it sounds like the engine may be OK, valve seals would not be a major deal.
 
I am using 15w40 rotella t. oil pressure is 40-50 on cold start up,then around 20-30 at idle. The rear main seal is leaking some,and if i decide the engine is in good condition,i will be replacing the rear main. I just hate to do the work and then have to pull the engine for a different one anyhow if it isn't the rear seal causing the oil loss.
 
cjben said:
I am using 15w40 rotella t. oil pressure is 40-50 on cold start up,then around 20-30 at idle. The rear main seal is leaking some,and if i decide the engine is in good condition,i will be replacing the rear main. I just hate to do the work and then have to pull the engine for a different one anyhow if it isn't the rear seal causing the oil loss.
Click to expand...

I've only ever used rotella in diesels, is there any specific reason you're using it or is it just the oil you happened to have at the time? (not related to fixing your problem at all, I'm just curious).
 
rotella is a good oil,not just for diesels,i have had good luck with it in other vehicles i have had,i just stuck with it for my xj.
 
Have you checked inside your air filter box for the missing oil? Is the filter soaked with oil?

I'd take the valve cover off, clean it thoroughly and replace the CCV orifice (the back rubber plug on the valve cover) as a place to start since it sounds like the engine is still mechanically fine to me.

Later,
Joe
 
My CCV orifice was a brass plug on the side of the valve cover, it may be different over the years, as well, I have a 2.5L L4, the 4.0L L6 may be different as well.

Has anyone tried converting to a PCV system? My XJ is still in the garage with the last of the repairs and putting the interior back in it. But if my clean up of the CCV hasn't stopped the oil puking problem, I'm going to try to convert to a PCV system.
 
Smoke on start up is generally due to leaking exhaust valve guide seals. Smoke under power is from poorly seating oil control rings....I'm 100% with 87manche on doing the leakdown test....although it is possible for the compression rings to have decent seal and the oil rings not.

It is NOT from the type of oil. I hope you have been running an EFFECTIVE air filter...if the leakdown is good, make sure the ccv system is up to speed.
 
I have never done a leak down test. what tools do i need,and what is the procedure? and yes the air filter has oil in it,has been that way for the 2 years I have owned the jeep. I just now have the time to do some much needed TLC to the jeep. Oil in the air filter was the main reason i was asking if i could tell if the problem was the ccv or more serious.
 
have you fixed the blowby problem by replacing/cleaning the ccv system? i would do that before i would do a leak down test.

smoke at start up is usually valve guide seals.
 
cjben said:
My 1992 xj 4.0 is using one quart of oil about every 250 miles,more than that if i put a lot of highway miles on it. It has 180,000 miles on it. I did a compression test about 6 months ago,and all cylinders were between 130-140 psi and the plugs weren't oil covered,they looked normal. i am planning on doing some bolt on upgrades to sqeeze a few more ponies out of it before long,but I don't want to do it if the engine is toast. I know these engines are good for a lot of miles,but my xj shows signs of previous owner neglect. so the question is: Is there a way to tell if the blowby is the ccv problem,or something more serious? I have noticed the engine smokes on start up,but from what i can tell it doesn't smoke while i am driving it,and it still seems to have quite a bit of power. . thanks for the help,Ben
Click to expand...

I had a 1 quart/100 mile oil leak at the oil filter adapter recently that did not leak when parked, no oil spots on the driveway but leaked on the road. Replacing the o'rings in the oil filter adapter fixed the oil loss.

Some of your oil loss is into the air filter, but I doubt it is 1 quart/250 miles. Check the passenger side around the oil filter for a leak, it mimicks a real seal. If you have not done much maintenance on it yet, it may be the valve cover gasket, rear oil seal and oil filter adapter o'rings all leaking plus some on the exhaust valve guides/seals at start up (which makes sense since the spark plugs were clean). If you had serious oil blowby on the running engine the plugs would have shown signs of it!

Fixing all the vacuum leaks in the valve cover, intake manifold and CCV system should solve you oil in the filter problem but look to the valve cover, oil filter adpater and rear seal for the big oil losses.

I would rebuild the head when and if you do any manifold upgrades. Till then I would run it and fix the leaks.
 
Rick Anderson said:
My CCV orifice was a brass plug on the side of the valve cover, it may be different over the years, as well, I have a 2.5L L4, the 4.0L L6 may be different as well.

Has anyone tried converting to a PCV system? My XJ is still in the garage with the last of the repairs and putting the interior back in it. But if my clean up of the CCV hasn't stopped the oil puking problem, I'm going to try to convert to a PCV system.
Click to expand...

From what I have read here in an oem forum thread recently switching to a PCV valve system can makes things worse. It would also probably cause high, low, and variable idle speed problems.
 
cjben said:
I am using 15w40 rotella t. oil pressure is 40-50 on cold start up,then around 20-30 at idle. The rear main seal is leaking some,and if i decide the engine is in good condition,i will be replacing the rear main. I just hate to do the work and then have to pull the engine for a different one anyhow if it isn't the rear seal causing the oil loss.
Click to expand...

Your compression numbers and oil pressures are normal so I'd say your engine is pretty healthy. All you need to do is replace the valve stem oil seals, replace the rear main seal (can be done by simply removing the oil pan and the no.7 main bearing cap), replace the oil pump (at 180k miles it's well past its best), and address any other oil leaks you might have e.g. oil filter adapter o-rings.
Since you're going to remove the valve cover anyway, you can give the CCV baffles a thorough cleaning and do the same to the CCV elbows.
 
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