Engine smoke when whacking throttle
Thread Starter
Instructor
Joined: Sep 2008
Posts: 233
Likes: 17
From: Macon GA
Engine smoke when whacking throttle
Hope some of you smart engine guys can figure this out. 78 resto mod with a SBC 350 crate short block with Edelbrock aluminum heads. Engine has less than 250 miles on it. When I whack the throttle there is a buff of white smoke out of the right side header. Not continuous smoke but just a buff. Also a small amount of what looks like water droplets comes out of the header. All plugs look good except #4 & #6. Both are black and a little wet. Compression check and all cylinders are between 150 and 160. #’s 4 & 6 are at 150. Leak down test was negative. Cooling system pressure test was good. Engine runs strong except for the smoke and #4 & #6 plug issues. Because of the tests I don’t think it is a cylinder head. I used ARP head bolts and sealant on all bolts, at least I think I did. If I missed one could a head bolt without sealant cause this? Any ideas??
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Test coolant again ... perhaps also test for presence of combustion byproducts,
walks like a duck ... quacks like a duck ... it's a duck
water droplets ........ white smoke
In addition to comp check, have you performed a cylinder leak-down test ?
were both of block's decks milled/resurfaced ?
If heads were used, was each milled/resurfaced ? If New heads, was each checked for flatness/scarring ?
Which head gasket (brand pn) was used ?
Did you install with any self-applied sealant/coating. ? ... if so, which ?
walks like a duck ... quacks like a duck ... it's a duck
water droplets ........ white smoke
In addition to comp check, have you performed a cylinder leak-down test ?
were both of block's decks milled/resurfaced ?
If heads were used, was each milled/resurfaced ? If New heads, was each checked for flatness/scarring ?
Which head gasket (brand pn) was used ?
Did you install with any self-applied sealant/coating. ? ... if so, which ?
Thread Starter
Instructor
Joined: Sep 2008
Posts: 233
Likes: 17
From: Macon GA
Did leak down test on all four cylinders on that side. All results were good. Did the chemical block test for coolant contaminates - negative. Also loosing mo coolant. New GM crate short block. Edelbrock heads - both checked flat with no scaring. Edelbrock 7361 gasket set as recommended by Edelbrock.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Cylinders #4 & #6 are the center two on the right side. I would surmise that you have a stuck heat riser valve (stuck closed) and that those two cylinders and the head gasket got really hot and the gasket let go. White smoke when engine is revved. See if the heat riser valve is stuck. If so, you can fix it....or you can just drop the down pipe and cut the valve butterfly off of its shaft so it can't happen again. If you don't drive the car a lot in cold weather, there will be no loss of function...just a little longer for carb to heat up.
How do I know this? Don't ask.....
How do I know this? Don't ask.....
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
You never mentioned any coolant loss. So lets look elsewhere. Because all the coolant pressure tests seem to get a passing grade perhaps its another fluid being burned off.
Is this an automatic? There is a Intake vacuum port between cylinders 6 & 8. A vacuum line from your Intake might run down to the tranny modulator. Some do, some don't. If the modulator is defective, it will allow ATF be sucked up into the Intake, then to the closest cylinder (6). That would explain the fouled plugs.
If that ATF is burning, its most likely going to be white steam also.
Is this an automatic? There is a Intake vacuum port between cylinders 6 & 8. A vacuum line from your Intake might run down to the tranny modulator. Some do, some don't. If the modulator is defective, it will allow ATF be sucked up into the Intake, then to the closest cylinder (6). That would explain the fouled plugs.
If that ATF is burning, its most likely going to be white steam also.
Last edited by HeadsU.P.; Jan 11, 2020 at 05:06 PM.
Thread Starter
Instructor
Joined: Sep 2008
Posts: 233
Likes: 17
From: Macon GA
Thanks for the help so far. Smoke appears only when I whack the throttle and no noticeable smoke when idling or driving. It smokes like this when cold and when up to temperature. Car runs at about 200 degrees and has never gotten over 210. Headers so no heat risers. Automatic with the modulator vacuum is attached to the intake just in front of the distributor. Had a little weather issue yesterday so it will be later today before I can get back to it. Also #4 & #6 plugs are a little oily.
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
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
The vacuum port on most SBC is fed from the Intake Runner on the # 6 cyl and that cylinder only. So I have no explanation of a fouled #4 from any ATF being introduced from the tranny.
When I first read your post, I was leaning towards a faulty Intake gasket seal allowing coolant in at two adjacent cylinders. But you mentioned #4 & #6. No coolant passage port there. So now you are back to the head gasket question. But that too seemed to pass the test. IDK
When I first read your post, I was leaning towards a faulty Intake gasket seal allowing coolant in at two adjacent cylinders. But you mentioned #4 & #6. No coolant passage port there. So now you are back to the head gasket question. But that too seemed to pass the test. IDK
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Not so hasty. Let some members think on this first.
Is your coolant level dropping?
Getting back to post #1. Yes, if some of the headbolts did not receive thread sealant and cooling system builds pressure, coolant could work its way into the combustion chamber. But that would be a head gasket issue also.
Before I went to the trouble and expense of pulling the head, I would drain-off some coolant into a clean bucket. Pull the passenger Valve Cover. Remove at least the one head bolt between cyl # 4 & # 6 and apply ARP thread sealant, retorque. And maybe the headbolt on the bottom row too. Those are difficult to get at.
Is your coolant level dropping?
Getting back to post #1. Yes, if some of the headbolts did not receive thread sealant and cooling system builds pressure, coolant could work its way into the combustion chamber. But that would be a head gasket issue also.
Before I went to the trouble and expense of pulling the head, I would drain-off some coolant into a clean bucket. Pull the passenger Valve Cover. Remove at least the one head bolt between cyl # 4 & # 6 and apply ARP thread sealant, retorque. And maybe the headbolt on the bottom row too. Those are difficult to get at.
Thread Starter
Instructor
Joined: Sep 2008
Posts: 233
Likes: 17
From: Macon GA
Coolant is not dropping. Running 10W30 Lucas Hot Rod high zinc oil (flat tappet cam). Engine has about 250 +/- miles of break-in type driving. Nothing hard just a few mild road miles. No hard acceleration or high RPMs. Will try pulling/re-sealing/re-torquing a few bolts (one at a time) between #4 & #6 to give that a try.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Something tells me its not the head gasket. Maybe just a hunch.
A blown head gaskets symptoms can go two ways. Sucking coolant into the cylinder for one.
Blowing gases into the cooling system via the block is two.
Having said that, remove the Rad Cap and with a slightly high idle, observe the coolant as it passes by the Rads fill opening. Any unusual bubbles going by?
A blown head gaskets symptoms can go two ways. Sucking coolant into the cylinder for one.
Blowing gases into the cooling system via the block is two.
Having said that, remove the Rad Cap and with a slightly high idle, observe the coolant as it passes by the Rads fill opening. Any unusual bubbles going by?
Last edited by HeadsU.P.; Jan 14, 2020 at 07:25 AM.
Safety Car
Joined: Jan 2009
Posts: 4,000
Likes: 299
From: New York
You have to load that motor up the rpm scale varying it constantly , Put it in 3rd at a low speed and make it climb an incline down shift to 2 or 1 and force the motor to slow the car down . Never drive it like its a sundry drive to church . You might simply have 2 cylinders that did not seat the rings ..
Thread Starter
Instructor
Joined: Sep 2008
Posts: 233
Likes: 17
From: Macon GA
More information. I pulled the intake today and noticed the intake runners for #4 & #6 are visibly cleaner than the other runners. All others have some gas residue on them but #4 & #6 are clean and shimmy as they were when I put this thing together. The exhaust ports for #4 & #6 are black and sooty. #2 & #8 are clean. Will dig further tomorrow when I pull the head.
Last edited by Triton170; Jan 14, 2020 at 02:50 PM.
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
More information. I pulled the intake today and noticed the intake runners for #4 & #6 are visibly cleaner than the other runners. All others have some gas residue on them but #4 & #6 are clean and shimmy as they were when I put this thing together. The exhaust ports for #4 & #6 are black and sooty. #2 & #8 are clean. Will dig further tomorrow when I pull the head.
I was going to say throw a vacuum gauge on it, but you have already removed the intake.
It would not hurt to hit the coolant system with a pump up tester......this will eliminate 100% having to remove the heads as you have performed the leak down already........leak down is pushing out against the fire ring during the test......but when running you have vacuum and pressure of course.
Jebby
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
OP
? has anyone done any porting to head or intake ?
Unless you see that something's wrong with head, take head to auto machine shop and have them Zyglo check for crack / leak ...
... check/test its rocker stud holes for same ... have shop pressure test the head. Do likewise with intake manifold.
Closely inspect bores 4 & 6 when their pistons are at Bdc.
Closely inspect block's deck for fine crack ... especially between 4 & 6. ... and at any water holes.
? has anyone done any porting to head or intake ?
Unless you see that something's wrong with head, take head to auto machine shop and have them Zyglo check for crack / leak ...
... check/test its rocker stud holes for same ... have shop pressure test the head. Do likewise with intake manifold.
Closely inspect bores 4 & 6 when their pistons are at Bdc.
Closely inspect block's deck for fine crack ... especially between 4 & 6. ... and at any water holes.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
You mentioned in the first post, you have Eddy aluminum heads.
Jackson might be on to something here. So the question now is:
Do the Eddy rocker studs thread into #4 or # 6 port? If so, were they sealed with a thread sealer? On some brands, the threads of the rocker stud are actually visible looking through the port. Or if extensive grinding (porting) was done, someone could open up the port TOO MUCH, exposing stud threads.
Also, when you removed the Valve Cover, was any milkshake substance present anywhere on the head?
Jackson might be on to something here. So the question now is:
Do the Eddy rocker studs thread into #4 or # 6 port? If so, were they sealed with a thread sealer? On some brands, the threads of the rocker stud are actually visible looking through the port. Or if extensive grinding (porting) was done, someone could open up the port TOO MUCH, exposing stud threads.
Also, when you removed the Valve Cover, was any milkshake substance present anywhere on the head?