White smoke while coast - JeepForum.com
 
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post #1 of 6 Old 06-23-2021, 05:43 AM Thread Starter
lawsonej
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White smoke while coast

Is this a valve seal issue? 98 grand cherokee 4.0.

Dont see smoke at all on startup or while accelerating. But if I am coasting from 60mph to a stop, like you would at stop light... I see white smoke fanning out behind my jeep. Oil level doesnt seem to be dropping. Coolant is at proper level.

Any thoughts?

260000 miles approx.

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post #2 of 6 Old 06-23-2021, 06:03 AM
Delta0
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Quote:
Originally Posted by lawsonej View Post
Is this a valve seal issue? 98 grand cherokee 4.0.

Dont see smoke at all on startup or while accelerating. But if I am coasting from 60mph to a stop, like you would at stop light... I see white smoke fanning out behind my jeep. Oil level doesnt seem to be dropping. Coolant is at proper level.

Any thoughts?

260000 miles approx.
Apart from don't look, worn valve guides?

Could be oil from your PCV valve.
Try extending and lifting up the pipe from the PCV valve.
The nearer the lift is to the PCV valve the better,
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post #3 of 6 Old 06-23-2021, 06:51 AM
gutthans
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Is that coasting in neutral or with the engine in gear?
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post #4 of 6 Old 06-23-2021, 07:28 AM
zjosh93
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Typically they say white smoke = coolant and blue smoke = oil. But in the real world with modern oil it all pretty much looks white, especially in the rearview mirror.

That's a classic valve seal symptom. You can also let it idle for a long time and see if it starts to smoke.

The 4.0 isn't known to have valve stem wear issues. The motor in my 93 has over 300,000 miles and the valve stem wear is still fine. It had the blue smoke on decel and after a long idle. New seals fixed it and it's still fine after... ten years (wow time goes by).

FWIW if you have a dial indicator you can get a good feel for the valve stem wear by checking the radial play in the stem at the head when you replace the seals. Just set the indicator up perpendicular to the stem and wiggle it back and forth.

There are at least a couple threads on here about replacing valve seals. I prefer the rope trick because it's cheap and relatively fool proof.
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post #5 of 6 Old 06-23-2021, 11:44 AM Thread Starter
lawsonej
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Quote:
Originally Posted by zjosh93 View Post
Typically they say white smoke = coolant and blue smoke = oil. But in the real world with modern oil it all pretty much looks white, especially in the rearview mirror.

That's a classic valve seal symptom. You can also let it idle for a long time and see if it starts to smoke.

The 4.0 isn't known to have valve stem wear issues. The motor in my 93 has over 300,000 miles and the valve stem wear is still fine. It had the blue smoke on decel and after a long idle. New seals fixed it and it's still fine after... ten years (wow time goes by).

FWIW if you have a dial indicator you can get a good feel for the valve stem wear by checking the radial play in the stem at the head when you replace the seals. Just set the indicator up perpendicular to the stem and wiggle it back and forth.

There are at least a couple threads on here about replacing valve seals. I prefer the rope trick because it's cheap and relatively fool proof.
I have the hose that you put in the spark plug hole and pressurize with air and the spring compressor, I have heard of folks using these in the past, but I may be wrong. I appreciate your feedback. I might have to try the long idle time and dial indicator! Thanks
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post #6 of 6 Old 06-23-2021, 02:06 PM
zjosh93
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Yeah, those are the other way to do it. I just am wary of that method because if you lose the valve seal for any reason, the valve will fall into the cylinder. If you were unlucky enough the cylinder will be down all the way (air pressure tends to do that) and now you have to pull the head to get the valve back.
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