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  • Mystery steam from under exhaust manifolds

    Hi, I've got a bit of an enigma here that I need some advice on, and there's a bit of backstory to it that may help with any diagnosis. I've been searching for weeks and haven't found anyone experiencing similar problems. Here goes.

    I bought a 98 firebird with 73k on the clock for around $1700 back in January. Apart from a broken headlight motor gear, it was in really good shape, but the ownership history was sparse at best, and it seemed like it had been sitting for quite a while. In May, it started to spring a minor oil and coolant leak. I've since replaced the upper and lower intake manifold gaskets (really every gasket I could find apart from the head gaskets and exhaust manifold gaskets), and of course those have been sealed properly and torqued to specifications. I also replaced the infamous coolant elbows.

    I got the car up and running after 6 months (I'm in college, give me a break), but after running for five minutes or so, some steam started rising from underneath the exhaust manifold on the passenger side. I figured it could have been some PB blaster burning off from under the heat shields, since at one point I planned on removing the exhaust manifolds to replace the head gaskets, but ultimately never went further than applying lots of PB to the passenger side and a little bit of it to the driver's side. It also developed a small coolant leak from the front of the engine, and I ended up replacing the water pump (which was actually fine, if a bit old; the gasket was again the issue) along with the coolant temperature sensor.

    I thought the steam could have been related to air in the coolant, but after several runs I am certain that I've fully bled the coolant system and there should be no air pockets left, but the problem persists.

    I decided to try idling the car for as long as possible to see if either it was some condensation that needed to fully evaporate or some sort of crud burning off. After 20 minutes or so, there was less steam coming from under the exhaust manifold on the passenger side, which was good news, but additional steam started coming from under the exhaust manifold on the driver's side. I tried driving the car around the parking lot, and the temperature slowly rose from the regular 210 to close to 235, which isn't great.

    The strange thing is that there is NO steam coming from the exhaust pipes, and no external leak. No liquid is pooling anywhere, nothing is visibly getting wet. Furthermore, I'm unaware of any connections to the coolant system near the back of the engine. I THINK I can hear a slight sputtering sound from the area of the back of the passenger side valve rocker cover, something akin to water touching a hot metal surface and instantly evaporating, but with the sound of both the engine and the serpentine belt, it's hard to say for sure that I'm hearing a unique sound.

    I won't be able to get back to the car for a short while to jack it up and take a look underneath, so I'm just looking for more informed ideas of what could be causing the issue.

    A quick recap of important factoids:
    - car was probably left sitting for a long time with dexcool in it, which has eaten just about every plastic gasket. The radiator seems to have survived.
    - developed a coolant and oil leak from the lower intake manifold gaskets
    - intake manifold gaskets and coolant hose elbows (among other things) were replaced
    - coolant has been refilled and system has been burped, oil has also been refilled
    - after the system builds up some heat and pressure, steam starts rising from under the exhaust manifolds (and it is definitely steam, not smoke), which is a new issue entirely.
    - no error codes whatsoever

    Anyone have any idea what's going on here?
    Head gaskets? (Shouldn't be a problem now since they weren't the issue before, I never touched the head bolts, also no steam/white smoke from tailpipe)
    Freeze plugs? Knock sensor? Something else entirely?

    Is it worth running the car some more to see if it burns off or stops on its own? Should I get a professional coolant acid flush to clear out any potential blockages that could be causing this? Maybe a pressure test? Any advice is appreciated.

  • #2
    My first thought is knock sensors and frost plugs are in that immediate vicinity - however, leaks do have a tendency to run along surfaces, pool and drop out. Common leak areas are the elbow that goes into the lower intake manifold which you have said is bone dry and you have ruled out.

    Did you find and fix the coolant leak at the front of the engine? And I know you said you burped the engine - but you did burp the engine via the screw on the thermostat housing correct?

    If you absolutely can't find any wet spots and you are positive you correctly torqued down the manifolds and installed the gaskets...the next step would be to run a coolant die in it to identify where the leak is coming from. A shop certainly has the tools for this - you may be able to purchase a kit? ... powerwash/clean the block up...run the die in the car for a few minutes and put the black light on it to see where you have the die leaking from and you'll be able to trace back on the point.

    If you are seeing steam (not exhaust) though my notion is you have quite a large leak coolant leak - what is the level of your coolant at since running it?

    Also - put your hand over your exhaust - are you getting any exhaust hitting your hand at all? Posting a video may help us a little better as well and give us a bit of a visual.

    How is the car idling and running aside from the steam/leak/overheating issue?

    2002 SOM Z28 Camaro
    1996 3800 camaro- Gone - still the fastest N/A Canadian 3.8L F-body
    V6 best: 13.43 @ 100.77 mph


    My Current Build | Synthetic Oil | Videos

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    • #3
      Also - have you inspected the two lines passenger side that go back to the heater core?

      2002 SOM Z28 Camaro
      1996 3800 camaro- Gone - still the fastest N/A Canadian 3.8L F-body
      V6 best: 13.43 @ 100.77 mph


      My Current Build | Synthetic Oil | Videos

      Comment


      • #4
        Originally posted by LETZRIDE View Post
        Did you find and fix the coolant leak at the front of the engine? And I know you said you burped the engine - but you did burp the engine via the screw on the thermostat housing correct?

        ...

        How is the car idling and running aside from the steam/leak/overheating issue?
        I did fix the coolant leak at the front of the engine -- that was the water pump gasket. I did burp the engine via the screw on the thermostat housing. I've also replaced my thermostat, in case that's relevant.

        The car idles and runs just fine. This is actually my second firebird and my third V6 F-body, but the first one that's completely in my name and the first that I've performed such major repairs on myself, so I do have some context as to what they sound and feel like when healthy. Nothing unusual, and it responds well when I increase the throttle -- no extra steam or anything.

        Here's a brief video of what the steam was like before I tried running it for 20 minutes or so. There's about half as much steam coming out of it now, but it's coming from both sides, as I mentioned.

        The heater core hoses seem to be fine, I'll take a closer look at them next time I can, and I'll try a dye test.

        edit: forgot to mention, I am getting exhaust hitting my hand, there is definitely some healthy flow through there.

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        • #5
          Are you losing coolant ? Do you have to top off the radiator after you run it?
          08' L76 6.0L 4X4 Chevy EXT.Cab LTZ Vortec MAX with Snug top cover, Dynomax exhaust,Hptuners& K&N intake
          96' Camaro M5 to A4 conversion, alot of mods ,see Homepage. GT35R Turbo http://www.cardomain.com/ride/244123...vrolet-camaro/

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          • #6
            Originally posted by ssms5411 View Post
            Are you losing coolant ? Do you have to top off the radiator after you run it?
            I am not losing coolant, at least not at a detectable rate, but it could just be that I still have a lot of coolant in the overflow reservoir so it's hard to tell.

            I probably won't be able to try anything new with the car for a few weeks, since I'm away from home on vacation, but I'll keep everything mentioned so far in mind to run a new batch of tests when I get back. It's pretty awkward to get everything figured out on a car with one exception and then be separated from it and have nothing to do but try to make sense of the information I've gathered so far. I'll be puzzling over this one for a while, so any ideas help.

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            • #7
              I didn't see you mention them specifically, but you did say you replaced most of the gaskets in your opening post; have you replaced the valve cover gaskets? Your description about something at the back of the valve cover on the passenger side makes me think you've got a tiny bit of oil squeaking out consistently as the engine runs.

              They're a pretty common gasket to go with age and usually result in small leaks that run down your cylinder heads over time and make everything look pretty grimy.

              Are you losing any oil at all?

              Comment


              • #8
                Originally posted by Namrepus28 View Post
                I didn't see you mention them specifically, but you did say you replaced most of the gaskets in your opening post; have you replaced the valve cover gaskets? Your description about something at the back of the valve cover on the passenger side makes me think you've got a tiny bit of oil squeaking out consistently as the engine runs.

                They're a pretty common gasket to go with age and usually result in small leaks that run down your cylinder heads over time and make everything look pretty grimy.

                Are you losing any oil at all?
                I have replaced the valve cover gaskets, and I'm not losing any oil at all.

                Comment


                • #9
                  Your losing something, either oil or coolant.
                  08' L76 6.0L 4X4 Chevy EXT.Cab LTZ Vortec MAX with Snug top cover, Dynomax exhaust,Hptuners& K&N intake
                  96' Camaro M5 to A4 conversion, alot of mods ,see Homepage. GT35R Turbo http://www.cardomain.com/ride/244123...vrolet-camaro/

                  Comment


                  • #10
                    It's been a while now and I'm finally back in town, I haven't been able to get any dye yet, but I did prop the car up on jack stands and got to take a look under it. Nothing suspicious whatsoever. No drips, nothing wet or shiny and not even any visible steam from underneath the exhaust manifolds. I can rule out freeze plugs too. My updated theory is that I may have put too much oil in it, since the oil pressure is a few ticks above normal and after it starts steaming it drops to below the center of the dial. Also, the dipstick indicates that it's way past full.

                    I drained all the oil, which I found to be surprisingly darkfor me having driven the car all of 0.2 miles (though I also ran it while parked around a dozen or so times), but it wasn't quite black and had its regular viscosity, so I put 2/3 of it back in and topped it off with a bit of clean oil, and now the dipstick is no longer reading far beyond full. Also worth noting, there was nothing out of the ordinary in my oil, it was a regular color, and no coolant or particulates were present.

                    I started the car, and the oil pressure was still a little bit above the center line, but was below where it was before, and it held steady. I kept the car running for around 20 minutes or so, like before, occasionally revving it at maybe 1500 RPM. The amount of steam/smoke/whatever it was was drastically reduced, and I managed to get the car up to a healthy operating temperature of 210 degrees without any at all. I revved it for an extended period and managed to produce a very small amount of steam, but it was essentially negligible. I also burped the coolant one more time and there seemed to have been a few bubbles.

                    No matter what I did, I couldn't budge the temperature higher than 210, which is great compared to the last time I tried running it for more than 20 minutes, when I drove it slowly around the parking lot and the temperature rose steadily to 235 and above and wouldn't go down.

                    So, while I never did locate the origin of the steam/smoke, I'm tentatively declaring the firebird operational, but I'll post back here if the issue arises again. I'm not entirely sure why oil pressure seemed to account for this, or if it was changing the oil or the few small bubbles I got out of the coolant (seems unlikely since I did that after getting it up to 210 with no steam), but I suppose high pressure causing a leak somewhere would make sense. If anyone has a more technical explanation or idea, that would be appreciated.

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                    • #11
                      Take into account as well that when you are working on the motor a lot of grease from your hands gets on the exhaust pipes and manifolds...as the engine warms up it will billow smoke for awhile...I remember this scared the shit out of me the very first time it happened.

                      Since you burped the system again and there was some more air pockets I am wondering if that was the reason your temp was rising above 210 as air pockets will cause that.

                      How much oil did you initially put in? I still don't see how overfilling the oil would cause steam, unless it was leaking down and out from somewhere? But you also said you don't see any leaking or wet spots.

                      Keep in mind as well the accuracy of our oil pressure gauges isn't the best so I wouldn't put too much weight behind where your needle may be lingering except for if it is pointed in an extreme direction (I.e indicating no pressure or max pressure) ...if you want a proper reading unfortunately you'll need to use a mechanical gauge for that reading.

                      2002 SOM Z28 Camaro
                      1996 3800 camaro- Gone - still the fastest N/A Canadian 3.8L F-body
                      V6 best: 13.43 @ 100.77 mph


                      My Current Build | Synthetic Oil | Videos

                      Comment


                      • #12
                        Glad you figured it out, but like already said, over filling wouldn't of caused it, maybe a valve cover gasket. Your coolant however would definitely heat up more if it wasn't bled correctly.
                        08' L76 6.0L 4X4 Chevy EXT.Cab LTZ Vortec MAX with Snug top cover, Dynomax exhaust,Hptuners& K&N intake
                        96' Camaro M5 to A4 conversion, alot of mods ,see Homepage. GT35R Turbo http://www.cardomain.com/ride/244123...vrolet-camaro/

                        Comment


                        • #13
                          Good advice. I'm here to close this thread with what seems to have been the real, FINAL solution to my problems.

                          My previously mentioned actions had reduced the amount of steam, but didn't eliminate it entirely. I think bleeding the coolant was really what was doing it. I suspected that it had something to do with having erroneously filled the coolant overflow reservoir completely before filling the radiator and bleeding the system a month or so ago, especially since the coolant dipstick was always reading way past full.

                          So I lowered a length of tube exactly as far into the coolant reservoir as the "full when cool" line on the dipstick indicated, and siphoned out around a quart and a half of coolant before reaching that level, and lo and behold, it worked! I drove around town, on the highway, got everything up to temperature and at no point could I smell coolant or see steam, even when idling and checking under the hood, in stark contrast to before. I suppose there's a dumb lesson to be learned about checking fluid levels, since I never suspected overfilling the reservoir could have such an effect. I still have no idea where the steam was coming from, but I suppose that's not really an issue anymore.

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