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M42 running hot after mess delete

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    M42 running hot after mess delete

    Hi all,

    So a few days back I dealt with the mess under the intake for my little motor. I replaced all the hoses that needed to go back in with new ones from fcpeuro. With that I also replaced the water pump, thermostat, fan clutch, expansion tank, along with any gasket that was removed. So after refilling and bleeding to the best of my ability, I took it around for a couple drives and each time the temp would climb pass the 1/2 mark and stay steady between there and the 3/4 mark. Thats the issue I’m having and I just wanted to see if I might be missing something or bounce some ideas. heres what Ive done and observed while trying to solve the issue
    • fan clutch doesnt seem to engage, however it is new and I've read that it might be a dud from the factory. I doubt that though because i threw on the old one to see if it would work but it also did not engage. Perhaps both are bad?
    • Took out radiator and flushed it thoroughly with a hose. I read that a reason for the clutch to not be engaging is that the radiator may be clogged up with gunk, which could also be a reason for it running hot. Still nothing even runs at the same temp while on the highway which kinda eliminates the fan clutch as the main culprit because it should run at operating temp on the highway just off wind right?
    • New expansion tank leaking from the lower seal when the cap is off or the bleed screw is open. The old tank did this too and the main reason i decided to tackle this job in the first place. Could this leak be causing it to run hot because it might leak pressure?
    Could it possibly be the thermostat got gunked up or should i flush the block out. Maybe a turn for the worse the head gasket is shot, but thats a long shot i hope because the car doesn’t smoke or lose coolant really. Let me know if y’all can think of what it is, whether its thermostat or fan clutch or anything else. Sorry for the lengthy post, thank you.

    1. make sure fan blades on the clutch is not installed backwards.
    2. What gasket did you use for the thermostat housing?There is a small passage that is used for bleeding and if clogged, you will have a hard time bleeding the system.
    3. The leak could be due to pressure.
    4. Make sure the car is bone cold before you try to bleed it a second time. The longer it runs, the longer you will have to wait, possibly overnight.
    Alex 88 m5 | 91 318is | 19 Subaru Ascent
    BMW Tool Rentals & Fender Roller


      Did you figure this out?


        Originally posted by dlmrun2002 View Post
        Did you figure this out?
        Yes, somewhat. Since I posted this I've replaced the radiator+expansion tank with a new nissens unit, replaced the tstat housing gasket again + another tstat o ring(cleaned off any rtv and did not use any this time around), made sure that small passage was clear of any debris, and refilled with 50/50 bmw blue +distilled water. After that I unsuccessfully bled the car several times, it wasn't until a couple days ago (2 weeks later) that I was able to get a good amount of bubbles/ air out of the loop. Now its been running like a champ (after two days of 1hr+ test drives), the gauge creeps past the 1/2 mark about a needles width when warmed up. I figure it might have one last stubborn air pocket somewhere keeping it a little hotter.

        So the issue seemed to be that the system needed to be bled, thoroughly. Unfortunately, it seems that it has to be bled many times to completely free of air. Which can take several days, as you need to let the car cool down completely before you can bleed again. Another thing, I was unsure of what to do for the tank leak and was unsure of the radiators condition so thats why I opted to replace it with a new unit to eliminate that variable from the equation. Good luck on the bleeding its by far the most frustrating process I've had to deal with on the car. Apologies that I didn't respond sooner I hardly check the forums, and let me know if any of this makes any sense or helps at all.

        This is the process I followed for bleeding:

        Originally posted by KenC View Post
        Jack up the front of your car.

        Take off the cap and bleed screw.

        Turn temp selector to high heat (fan off).

        Fill with coolant mix until the reservoir is nearly full.

        Put cap and bleed screw back on. You need a closed system, or your coolant will boil.

        Turn car on and warm up until thermostat is open (radiator return hose will begin to fill and get very warm).

        Give your car a few good revs and slowly open the bleeder screw. Close and repeat a few times until you have no more air bubbles. Sometimes you have to rev it quite a bit to force some of the bubbles through.

        Let your car cool off completely and assess coolant level in reservoir (there is a cold fill line).