Help! Enough smoke to fog mosquitos

[Gatorbait]

Hi Folks, First post but have been lurking for a couple of weeks.

I recently purchased a 1985 C4 but the previous owner was not very helpful when asked questions after I bought it from them.

I immediately changed the oil to synthetic not know what they were using, and now it seems to get a puff of smoke while idling at a stop light.
Yesterday I was stuck in rush hour traffic and the exhaust was putting out enough oil smoke to be a mosquito fog machine.

Is it the valveseals and how much would it cost me to repair?

Or can it be the synthetic oil and I should change it back to regular motor oil?

Thanks

 

[Ron59]

Valve seals usually only cause smoke on startup or when the engine is holding back during deceleration. For the oil as long as it is the proper grade(10W-30 or 5W-30) syntetic or regular should be no problem. If it smokes alot I would do a compression check. If you have any cylinders that read low just squirt in a bit of oil and re check .. if the reading stays low the problem is with the valves .. if it improves the problem is with the rings. All 8 cyl should read within 10% of each other.

 

[LongBeachC4]

I run Mobil 5-30 no problems

 

[vetteoz]

For the oil as long as it is the proper grade synthetic or regular should be no problem.

Synthetic oil often causes " leaks" on older engines in places that didn't have them before because it's smaller molecules can get through spaces Dino oil can't
Also because of it's different detergents it may "wash" away sludge deposits that are sealing a existing leak

Valve seals usually only cause smoke on startup or when the engine is holding back during deceleration.

If the guide seals are shot a engine will suck in and burn plenty of oil at hot idle.
When a couple of mine went out at the track ( damaged by installing higher lift rockers than put the valve seal into contact with previously unused part of valve stem )
I had more smoke out the exhaust pipes than from the burnout :ugh

 

[Hib Halverson]

Synthetic oil often causes " leaks" on older engines in places that didn't have them before because it's smaller molecules can get through spaces Dino oil can't

(snip):ugh

Sorry but that's not correct. A myth propagated by folks who are not well informed about modern engine oils.

With this smoking 85...the fact that the previous owner was less than communicative about the car post-sale indicates a good chance he/she knew about the problem and took some measures to conceal it. Examples would be going to a high viscosity engine oil, (say 20W50) or adding a "seal softener" to the oil.

With you changing to the correct viscosity, the problem which is causing the smoking became more evident.

"Vetteoz's" earlier comment about detergents is "partially" true in that if you have an engine which has not had periodic oil changes and has been operated in a manner which has allowed a high amount of "sludge" to build up in the rocker covers, an oil change which (regardless of the oil base stock) puts "fresh" detergents in the engine, can cause larger pieces of sludge to be dissolved but...that doesn't happen immediately and this smoking problem started right after the oil change.

Again, my guess is the engine could have had high vis. oil in it to cover up the problem. I've even heard of people mixing SAE90 or 140 gear oil with engine oil to conceal and engine oil consumption issue.

Best bet is to troubleshoot the engine and decide if the smoke is caused by a problem with valve guides or piston rings.

My guess is that, sadly, you're looking at either a valve job or an engine overhaul.

 

[Gatorbait]

Thanks for the replies.
I am at a loss with this. As long as the car is in park/neutral or driving and not stopped too long in gear at a light, no smoke.
But if it has to sit for more than 5 min in gear in traffic or at a light, it will start sending smoke out the tailpipes.

My thought on the synthetic was it loosening up old sludge, but again, I am not a mechanic. I wanted a Vette to drive and have fun, not be working on it.

Monday, I will take it to a Corvette Mechanic who struck out on his own from one of Rick Hendrick's Chevrolet dealerships.

 

[Gatorbait]

What is the item on the passenger side valve cover, not the oil filler cap? There are 2 rubber elbows that do not look right and I would like to replace them

 

[vetteoz]

But if it has to sit for more than 5 min in gear in traffic or at a light, it will start sending smoke out the tailpipes..

As mine was doing with the bad valve seals

 

[vetteoz]

What is the item on the passenger side valve cover, not the oil filler cap? There are 2 rubber elbows that do not look right and I would like to replace them

Should be a PCV supply line from rocker cover to the top port ( pas side ) of the TB
The PCV valve should be in drv side cover and T'ed into a vac line to the intake

 

[Gatorbait]

I picked up a rubber elbow yesterday and put it on. I was thinking PCV, but this is on the passenger side.
I took the Vette around the block so to speak and watched for smoke.
My oil pressure was steady at 80 while driving and would drop to 60's when at a light.
The evening was cool, and the engine temp stayed low. No smoke
I returned to the house and kept the car in gear enough to raise the temp and simulate sitting in traffic. I heard the fan kick in around 230 degrees and it brought it back down to under 220. Still no noticeable smoke.
When I put the car in Park and revved the engine, I got a giant puff of smoke that fogged the yard.
It seems the smoke only happens at high temp.

 

[Schrade]

You might have put too much oil in it, and the crankshaft is spinning through it, and foaming it up. BAD BAD BAD! Oil pickup will get foamy oil, and not enough oil gets pumped. Pressure will be low / erratic.