Exhaust Smoke after start up (1971 Buick Skylark, SBB)

Discussion in 'Small Block Tech' started by bob1090, Jul 18, 2017.

  1. bob1090

    bob1090 Member


    I’m looking for some advice/suggestions regarding where or what I might look into next to solve my exhaust smoke problem on my ’71 SBB. The smoke almost always appears 30 seconds to a minute after start-up and is usually blowing out a heavier white smoke from the drivers side exhaust, but sometimes comes out pretty heavily from both exhausts.

    Yesterday I decided I’d pull her out to do some compression checks and coolant and oil level checks, but noticed it wasn’t smoking too much so I took her for a ride first. By the time I got back for a quick 5 minute drive a light white smoke had appeared from both exhausts. Compression check with engine cold checked out ok (all cylinders above 120psi with exception of one at 115psi). Oil level appeared to be slightly low, but nothing seemed out of the ordinary (Oil looked like oil). Coolant was about 6 inches below the top of the radiator cap, so I filled it up knowing there’s an overfill tank, but noticed that the coolant looked a dark brown milky color. I had flushed and replaced the coolant last spring after I installed a new cam, rockers and year correct lifters and push rods that the previous owner had goofed up on. Anyhow, I don’t think the coolant should have gotten that dirty that quick, right? I only drove it about 1000 miles since the coolant was replaced. I haven’t witnessed any leaks or drips on my driveway and she’s always ran right around 195 once warmed up. I’m not excited to rip it apart, but I’m assuming the low level of brownish coolant and exhaust smoke sounds like a head gasket. Any thoughts?


  2. MrSony

    MrSony Well-Known Member

    Replace headgaskets. Oil is getting into the coolant. Don't drive it anymore than you have to. You'll need to replace the headgaskets, and completely flush the cooling system. 120psi seems about 30psi too low imo. May be due for a hone and re-ring as well.
  3. alec296

    alec296 i need another buick

    Check your tailpipes and spark plugs. If you are burning coolant you will see it basically steam clean the inside of the exhaust and the spark plugs to confirm the head gasket failure. if the engine overheated head gaskets are practically a given for failure .
  4. Mark Demko

    Mark Demko Well-Known Member

    Pressure test the cooling system
    sean Buick 76 likes this.
  5. Fox's Den

    Fox's Den 27 years of racing the same 355 Buick motor

    Or do a leakdown test
  6. bob1090

    bob1090 Member

    Thanks for the responses. I had intentions of performing a leak down test on the cylinders last night, but the cheap leak down tester that I picked up was "calibrating" with only 15-20psi going through the line and the regulator on it wasn't exactly working the greatest either, oh well. So I hooked up 100 psi of shop air to the first cylinder at TDC and could hear air hissing out pretty good from the oil fill cap on the valve cover as well as from the oil dipstick. That, along with the dirty coolant, was all it took for me to start tearing her down. All I had time for last night was draining the oil and coolant and yanking the radiator. The oil didn't give me any further insight to my problems. I drained it cold thinking that if there were water it'd come out as soon as I pulled the oil pan plug, but there didn't appear to be any sign of water/coolant. However, when I drained the coolant it become a hole different story. It definitely appears that there's a little oil getting in the coolant, but it also looks like there's transmission fluid getting in there too! The coolant that actually made it in my collection pan and not on my garage floor looked mostly milky brown with some very red colored swirls in it.

    I'm not an experienced mechanic by any means, but I'd like to think that I'm mechanically inclined. That being said, any advice to steer me in the right direction without having to break my bank to get her up and running again would be great. I'm thinking that I'm probably going to need a new radiator though because as far as I know that's the only place transmission fluid could get into the coolant. I suppose I could rig up a pressure test of the transmission cooler ports on the radiator to be sure. Can I just flush the tubes running to the heater core with a water hose? I know I'll have to wait to flush the block until I inspect the head gaskets so I don't get water/coolant in places it shouldn't be.

    Next, I'll have to inspect the transmission fluid. If I find any water I'll have to post again to figure out the best way to flush the trans system because I've never done it before...

  7. alec296

    alec296 i need another buick

    Yes looks like you need a radiator.
    Check your spark plugs. See if any are much cleaner then the rest. That can tell you which cylinders may be burning coolant. If you find some that are caked with crumbling black chunks it maybe oil it's burning. Considering your hearing air leak thru valve cover, sounds like it may be burning oil due to ring wear. I would finish the leak test on all cylinders. That would give you more info
  8. Mart

    Mart Gold level member

    White smoke out the tailpipes sometimes means bad trans modulator. Pull line from trans modulator and the end should be dry! If trans fluid is detected, you are sucking in trans fluid into engine and burning it, hence the (James Bond) white smoke.
  9. bob1090

    bob1090 Member

    New leak tester was picked up yesterday, so I'll finish that before I tear it down any further. When I had plugs out for compression test they were all equally black. No crumbling black chunks, but very black so I'm assuming its burning a little oil.

    I haven't pulled the trans modulator, but I ruled that out another way by pulling the trans modulator vacuum line from the intake manifold for a minute while it was running to see if the smoke would stop. No luck.

    I'll come back with updates when I find time to work on it all some more!
  10. alec296

    alec296 i need another buick

    Black plugs usually means it's running rich. And check trans line that way isn't accurate. Under vacuum it forms a siphon. Pulling fluid even with engine off. You would need to run it for an hour to burn off what has been siphoned into the cylinders overnite. Piston may have a puddle on it.
    If all plugs are black and no 'steam cleaned' spark plugs it's more then likely not coolant. have you checked the trans fluid and oil? If your burning that much one would show low by now. Kinda going with Mart on this. Plug trans line and run it.
  11. bob1090

    bob1090 Member

    Good point, for some reason I was thinking that if trans fluid was being sucked into the intake through the vacuum line on the manifold that it'd be getting burned up right away. I'll pull the vacuum line off of the trans modulator and inspect. Any ideas for testing the trans modulator without running the engine though?

    I don't want to run the engine again before I tear it apart and clean this brownish red coolant out of it and I don't want to flush the block until I know the status of the head gaskets. I really need to finish that leak down test to see if I can gain any further information first.

    I did check my oil before I drained it and it was a tad low (halfway between full and add a quart) and I'll admit that I never really checked the trans fluid this season while the engine was at operating temperature. At the end of last summer when I checked it at operating temperature I know it was fine. The coolant was very noticeably low though, so it's going somewhere. But like I said, the coolant doesn't really look like coolant. It's brownish red so maybe that's why my plugs aren't looking clean?
  12. MrSony

    MrSony Well-Known Member

    Don't run the engine. Get the gaskets sorted out first. A little ATF isn't going to hurt anything while it's running after you address the leak until you can get to it.
  13. bob1090

    bob1090 Member

    I finally received the leak down tester I ordered and was able to test all cylinders yesterday. I had gotten antsy before I received the tester and removed the radiator, fan, alternator and distributor because I knew I was going to yank the heads after I did a leak test anyways because MrSony had mentioned that the compression seamed a little low and based on my other observations I was suspecting a head gaskets was the problem.

    Here are my results for compression(engine warm, all plugs removed, throttle plate fully open) :
    8. 117psi ; 7. 115psi
    6. 122psi ; 5. 130psi
    4. 115psi ; 3. 115psi
    2. 120psi ; 1. 120psi

    Here are my results for leak down (engine cold because half taken apart, all plugs removed):
    8. 8% ; 7. >60%
    6. 11% ; 5. 14%
    4. 9% ; 3. >55%
    2. 9% ; 1. 12%

    I was honestly expecting to see a correlation between leak % results and compression results, but I guess not. Cylinders 3 and 7 are obviously an issue.

    When testing cylinder 3 I could hear air leaking out of the whole in the timing cover where the distributor was removed from. I plugged that whole and attempted to determine where it would then leak from, but couldn't pinpoint it. You could hear some coming out of the oil cap on the valve cover, but most of it sounded like it was making it down into the crankcase and escaping from there somewhere. I'm assuming this is indicative of a bad ring on 3rd piston?

    When testing cylinder 7 I could hear air coming out of the adjacent spark plug holes. Perhaps a bad intake or exhaust valve?

    What should I do next? Anything else I should do before I pull off the heads?

    I've also attached a picture of my plugs and the thermostat and thermostat housing that's covered in the nasty colored coolant which I'm still unsure if it's from transmission fluid, oil or rust...



  14. Fox's Den

    Fox's Den 27 years of racing the same 355 Buick motor

    Those leak down numbers look like my brothers Mustang with the Procharger on it. He was pushing oil out the dipstick and the radiator started pushing water out the filler cap. Looks like it is time for a rebuild.

    On my motor I have 10.6 compression and I hit about 190-95 on the compression test. The last leak down test I did was 5-8 % leakage in all cylinders. That was after running nitrous for a summer. Need to do a new one now since that was about 7-8 years ago.
  15. sean Buick 76

    sean Buick 76 Buick Nut Staff Member

    Sorry to say it looks like rebuild time... If you want re do the compression tests with some oil squirted into the plug hole and if the numbers jump right up it confirms the rings are leaking bad... Even a worn out but healthy 350 should be over 150 PSI on the compression test I think.
  16. bob1090

    bob1090 Member

    Ya, that's the response I expected. I've never pulled an engine or transmission, but I have to admit I'm sort of excited to do it and investigate before I most likely take it to a machine shop. Based on the little bit of poking around I did I'm assuming I'll get the valve seats done, the crank balanced and the cylinder walls honed or bored if needed. Since I've never done this before, can anyone estimate about how much that'll run me? I'm in the Buffalo, NY area.

    Aside from the machine shop costs I'd like to get a little bigger cam in there and as long as I have the engine out, maybe a torque converter? It has a TH350 transmission. I'm really hoping I don't need any boring and can stay away from purchasing pistons, but that seams unlikely. I feel like I'm in over my head on this one, but hopefully I can make it through this without breaking the bank!
  17. alec296

    alec296 i need another buick

    I would say if your losing compression past rings you will need an oversized bore. I suggest you research Pistons. A lot of stock replacement Pistons will have lower compression then stock as they sit lower below deck then the factory piston.

    Change cam bearings. Don't use the hi volume oil pump kit as it can wear front cam bearing . I suggest drilling out the oil pickup screen passage to oil pump in block to 1/2 and get a melling 20-IS5 pickup. It's a bigger tube from a 76-80 350.
    Do not have shop bake heads to clean. It's been mentioned that it can cause issues of cracks on the early heads.
    8ad-f85 likes this.
  18. 8ad-f85

    8ad-f85 Well-Known Member

    With a cylinder under pressure, bad valves will hiss out the air the carb or tailpipe direction.
    It is still possible to hear them from the other holes, of course but...
    Coming out the adjacent plug holes is sounding like blown head gaskets and/or cracked block/head between the cylinder, based on the rest of your description.
  19. alec296

    alec296 i need another buick

    Maybe running the test again on the questionable cylinders.
    8ad-f85 likes this.
  20. bob1090

    bob1090 Member

    I ran the tests again on cylinders 2 and 7 and got the same results. I had time to pull the intake and drivers side head last night. I don't see anything wrong with the head gasket. I was actually hoping I would because now I'm afraid there may be a crack somewhere that's causing my coolant to get all sludgy.

    Here's a picture of what was left at the bottom of the pan I used to collect the coolant. It sat in this pan for a day and this sludge settled to the bottom. I can only imagine what the bottom of my engine looked like right now...

    Is it normal for this much oil to be on top of the intake gasket?

    Here's the cylinder head I pulled. I couldn't find any damage to the gasket (still on the head in the picture). The cooling passages are a bit brown/rusty/dirty as expected. Are those two "L" shaped cavities on the intake surface just empty holes? They were full of oil and gunk. The exhaust valve looks a bit whiter on the two cylinders that had poor leak down results.

    The piston walls actually looked to be in pretty good shape(no scoring or ridges). Maybe I'll get lucky and not have to have them bored?

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