Excessive Exhaust Smoke.
Thread Starter
Drifting
Joined: Feb 2000
Posts: 1,591
Likes: 53
From: Central MN
Excessive Exhaust Smoke.
Is it normal for older high performance engines ('70 L46) to smoke excessively upon a cold start? Given the fact that these engines are carbureted and have little or no anti-pollution devices, I'd guess that excessive smoke is normal. Once the engine warms up, the smoke goes away. Anybody have any insight?
By excessive I mean you can see and smell the exhaust.
By excessive I mean you can see and smell the exhaust.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Assuming that the smoke is a bluish color, the valve guides or seals are bad on the car! When the engine is shut off, oil is running past the seals and in to the cylinders. This is a common problem with most C3 engines that have some years on them.
When you are starting up the engine the oil that passed through is burning off. Not an easy fix but something that can be tolerated until the car needs to be torn down.
I would keep a good eye on the oil consumption and then base my repair on this. Should the engine seem to consume mass quantities of oil, then I would consider pulling the heads and having them rebuilt. But. . . If the car is high mileage and you have the funds, instead of pulling the heads off I would consider a complete rebuild.
Willcox Inc.
When you are starting up the engine the oil that passed through is burning off. Not an easy fix but something that can be tolerated until the car needs to be torn down.
I would keep a good eye on the oil consumption and then base my repair on this. Should the engine seem to consume mass quantities of oil, then I would consider pulling the heads and having them rebuilt. But. . . If the car is high mileage and you have the funds, instead of pulling the heads off I would consider a complete rebuild.
Willcox Inc.
Thread Starter
Drifting
Joined: Feb 2000
Posts: 1,591
Likes: 53
From: Central MN
Everybody.........Thanks for confirming my suspicions. I knew it was a long shot, but I was hoping the smoke was normal.
My High School Auto Mechanics teacher (Mr. Richie) preached never do just a valve job. His logic was that parts wear in conjunction with each other. Therefore, if you fix the valve problem, you'll increase the compression and cause piston ring problems. Is there any truth to his logic?
To do the job correctly, the engine should be rebuilt. However, from a financial point of view, a valve job alone is much cheaper. Down the road, if I have just a valve job done, will I regret not spending the money on a complete rebuild?
Although I doubt it is accurate, the odometer reads 37K miles. Based upon the overall condition of the car, I highly doubt it has 137K miles on it. At what mileage point is it common for a C3 engine to need a valve job?
Wilcox Corvette...........Bought some weather stripping from you a few weeks ago. Excellent quality and fit!!!!
My High School Auto Mechanics teacher (Mr. Richie) preached never do just a valve job. His logic was that parts wear in conjunction with each other. Therefore, if you fix the valve problem, you'll increase the compression and cause piston ring problems. Is there any truth to his logic?
To do the job correctly, the engine should be rebuilt. However, from a financial point of view, a valve job alone is much cheaper. Down the road, if I have just a valve job done, will I regret not spending the money on a complete rebuild?
Although I doubt it is accurate, the odometer reads 37K miles. Based upon the overall condition of the car, I highly doubt it has 137K miles on it. At what mileage point is it common for a C3 engine to need a valve job?
Wilcox Corvette...........Bought some weather stripping from you a few weeks ago. Excellent quality and fit!!!!
Last edited by Cosmo Kramer; Aug 16, 2007 at 09:16 AM.
Le Mans Master
Joined: May 2006
Posts: 7,708
Likes: 266
From: indy indiana
No, it is not normal.
I agree,check the color of the smoke.
I doubt if its water (white), that usually doesnt go away after warm, and doesnt smell like fuel ,nor oil.
A puff of blue smoke at start-up ( after sitting for a while),is almost always valve guides/seals. Larger the cloud and the longer it last, worse the problem.
Continuous blue smoke...get out your wallet for a complete rebuild.
Black smoke and /or smell at start-up. You shouldnt really be able to see any at all. The smell...well..its running rich cause its cold/ choke closed, ect.
I think you may have a combo of problems.None really bad except on the wallet and it CAN wait till winter.
I agree,check the color of the smoke.
I doubt if its water (white), that usually doesnt go away after warm, and doesnt smell like fuel ,nor oil.
A puff of blue smoke at start-up ( after sitting for a while),is almost always valve guides/seals. Larger the cloud and the longer it last, worse the problem.
Continuous blue smoke...get out your wallet for a complete rebuild.
Black smoke and /or smell at start-up. You shouldnt really be able to see any at all. The smell...well..its running rich cause its cold/ choke closed, ect.
I think you may have a combo of problems.None really bad except on the wallet and it CAN wait till winter.
Le Mans Master
Joined: May 2006
Posts: 7,708
Likes: 266
From: indy indiana
Nope.you wont regret it. To do a full on rebuild, you have to pull the heads anyway.
Yes,at a 130K miles, that engine is getting a bit worn. Yes, the valves are usually the first indicator of rebuild time. Also, that timming chain is getting close to the " your gonna walk home tonight" stage. Heads off, timming chain off..great time to replace the cam.
Yes,at a 130K miles, that engine is getting a bit worn. Yes, the valves are usually the first indicator of rebuild time. Also, that timming chain is getting close to the " your gonna walk home tonight" stage. Heads off, timming chain off..great time to replace the cam.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Melting Slicks
Joined: Jan 2003
Posts: 2,713
Likes: 31
From: Shreveport LA
LA Events Coordinator
What if it's a new crate engine (GM Performance)? Mine has about 250 miles on it and it "blows blue-white smoke" when I first start it and it idles for a while. After running it (cruise etc), the smoke disappears for a while, then returns. Does she still need to be broke in?
Thread Starter
Drifting
Joined: Feb 2000
Posts: 1,591
Likes: 53
From: Central MN
I have nobody to be mad at, but myself. The seller assured me the odometer was accurate. He signed an odometer statement confirming the milage. Additionally, I paid an inspector $200. to check over the car (thankfully, all the numbers match) and confirm the odometer. Based upon his inspection, I understood the odometer to be correct. Bottom line: I paid way too much for the car. Live and learn, I guess.
Pro
Joined: Oct 2006
Posts: 545
Likes: 2
From: Peoplez Republik (communist portland) Orygun
Well...On with it!
1. What'd you pay for this car?
2. Can we see pics?
3. Welcome to the C3 forum
oh...C'mon, give yourself a break you bought a 38 year old car (matching numbers, chrome bumper Corvette). Of course it's going to burn a bit of color at start-up.
Instructor
Joined: Apr 2006
Posts: 212
Likes: 0
From: Woodland Park Colorado
It is very possible that the milage is accurate and have the problem with valve guide seals. The valve guide seals are rubber and over time from sitting they dry out and crack and have the smoke problem at startup. I think you need to check the motor out more as far as compression and such to see if all you need to to is change the seals. Seals can be changed without pulling the heads off. Good luck and welcome to the forum.
Le Mans Master
Joined: May 2006
Posts: 7,708
Likes: 266
From: indy indiana
What if it's a new crate engine (GM Performance)? Mine has about 250 miles on it and it "blows blue-white smoke" when I first start it and it idles for a while. After running it (cruise etc), the smoke disappears for a while, then returns. Does she still need to be broke in?
Thread Starter
Drifting
Joined: Feb 2000
Posts: 1,591
Likes: 53
From: Central MN
woodlandcorvette.........Yea, I guess your right. It is possible for the rubber valve seals to be worn out due to age and not necessarily high mileage.
Here are a few of the seller's pictures:
I paid $32.5 for the car. Given the fact that the car is an un-restored numbers matching car with 37K miles (?) I thought the price was fair. Personally, I'd give the car a rating of CC = -2.
Here are a few of the seller's pictures:
I paid $32.5 for the car. Given the fact that the car is an un-restored numbers matching car with 37K miles (?) I thought the price was fair. Personally, I'd give the car a rating of CC = -2.
Le Mans Master
Joined: May 2006
Posts: 7,708
Likes: 266
From: indy indiana
A set of valve cover gaskets, new seals( which are very cheap) and your good to go. They are easy to change and doesnt take that long. Do NOT over tighten the valve cover bolts.
Race Director
Joined: May 2005
Posts: 10,674
Likes: 122
From: Millington Illinois
St. Jude Donor '08-'09
Nice car, Nice color! If the mileage is correct and it hasn't been apart I would expect the valve seals to need to be replaced. The rubber breaks down with exposure to heat, oil and aging. No big deal. If the mileage is correct you bought the car at a fair price for a #s matching 4 speed 4.11 car.
Le Mans Master
Joined: May 2006
Posts: 7,708
Likes: 266
From: indy indiana
If you have never been inside valve covers before, you may want someone next to you that has.
Valve seals look like a cross between an umbrella and a bell mushroom. Made of rubber,of course. Look in a manual to see if you think you can do this work yourself.Its fairly simple and straight forward, but you do need a few special tools.You will also have to readjust the valves after doing this. The seal slips over the end of the valve stem. The end where the spring meets the rocker. Use caution not to drop the valve into the cylinder,there are several methods of doing that. With all that said, this isnt major brain surgery.
Seals can be purchased at almost any parts store,including your local chevy dealer. be sure to get the right year parts for the engine,as there are two different types of material used for seals, of which one may not last long in your application.
I really am saying this to others who may be in the same boat,but have little or no history of turning wrenches. Best of luck.
Valve seals look like a cross between an umbrella and a bell mushroom. Made of rubber,of course. Look in a manual to see if you think you can do this work yourself.Its fairly simple and straight forward, but you do need a few special tools.You will also have to readjust the valves after doing this. The seal slips over the end of the valve stem. The end where the spring meets the rocker. Use caution not to drop the valve into the cylinder,there are several methods of doing that. With all that said, this isnt major brain surgery.
Seals can be purchased at almost any parts store,including your local chevy dealer. be sure to get the right year parts for the engine,as there are two different types of material used for seals, of which one may not last long in your application.
I really am saying this to others who may be in the same boat,but have little or no history of turning wrenches. Best of luck.
