Minor pitting on head surface, using MLS gasket

[bflan2001]

I have some minor pitting on my rebuilt head around the coolant passage up front. I was told a little extra RTV during the installation will take care of it, but I'm using an MLS headgasket so I don't think I can use RTV. I also read to fill the pitting with JB Weld. Is that something I can do myself? I know the surface tolerance is super tight, not sure I'm comfortable sanding the JB Weld down.

edit: I just realized the pitting is where the profile gasket would go, not the head gasket. So I guess either option is viable, which would you recommend?

[DesktopDave]

+1 on the JB Weld.  It'll be stable and it's pretty easy to scrape off once it's set up.  Personally, I spread the mix on with some card stock and then use cling wrap to level it out.  It'll set up in about an hour depending on temperature, scrape it with a single-sided razor blade to level it out and let it cure for a day or so.

No sanding required.  Good thing too, it gets incredibly hard once cured.

[n2motorsports]

Zombie thread!

Just got my head back from machine shop with some pitting as well.  Hope this isnt too bad for jb weld?  Thoights?

https://photos.app.goo.gl/ZxZyCdooXCzTwKvX9
https://photos.app.goo.gl/GJ1PNnM5a4ZTuARi9

As you can see, the coolant ate thru, I checked with a flashlight.   Machine shop didnt think it was a big deal, and I kind of agree, since it's a closed system so some seepage from the head to radiator cant hurt.  Only thing blocking the coolant in the head is the thermostat, which opens at operating temps anyways?  Might take a few extra minutes to warm up, but I live in a warm climate so that should matter.  Ok, just ranting on now...thanks

[bmwman91]

I would not worry about that. There is a bypass groove in the thermostat housing cover at that location anyway. In fact, you WANT the passage to be open because it makes bleeding the system into a simple affair. All the stuff you read about the M42 being hard to bleed is nonsense. If the bypass is open, the system will force 95% of the air out after 30 seconds of idling. I don't even need to open the bleed screw in the radiator, simply having the cap off is enough. Just fill the system as high as you can until the level stops dropping before first start, start it and add coolant as it gets to the cold line and try to keep it around there. Revving the engine with a hand on the throttle makes it go faster. A long time ago I thought bleeding was hard, but that was because the bypass groove was totally full of RTV or something, so I had to wait for the engine to warm up and open the thermostat before air could get out.

[monty23psk]

I would not worry about that. There is a bypass groove in the thermostat housing cover at that location anyway. In fact, you WANT the passage to be open because it makes bleeding the system into a simple affair. All the stuff you read about the M42 being hard to bleed is nonsense. If the bypass is open, the system will force 95% of the air out after 30 seconds of idling. I don't even need to open the bleed screw in the radiator, simply having the cap off is enough. Just fill the system as high as you can until the level stops dropping before first start, start it and add coolant as it gets to the cold line and try to keep it around there. Revving the engine with a hand on the throttle makes it go faster. A long time ago I thought bleeding was hard, but that was because the bypass groove was totally full of RTV or something, so I had to wait for the engine to warm up and open the thermostat before air could get out.

+1, m42 is easy to bleed as long as that groove is not blocked, no apparent air leaks and the car is not parked at a declined. Just have a handy mix of coolant to keep adding. I learned with the e39, the way to bleed is to keep filling the system with coolant until coolant comes out the bleed screw.

[DesktopDave]

+3

I also use RedLine WaterWetter (or another surfactant like Royal Purple Ice, etc.) and mix the coolant with a little extra distilled water.

My M42 seemed to appreciate 33/66 ratio. Two gallons of distilled water, 1/2 bottle of RL WW, one gallon full strength/pre-mix BMW blue or Zerex G48 (~$20). Be aware that heavily diluted coolant carries risks: it can crack a block if it freezes, and it will have to be changed more often to prevent corrosion.

[bmwman91]

Interesting. What do you find about the WW and 33/66 ratio that works better? I live in a very mild climate, so straight 50/50 has always worked well in my cars.

[DesktopDave]

My primary goal with diluted coolant was to make bleeding easier. The thermostat bleed passage is far more important, but every bit helps. I've also found a very small increase in fuel mileage, approx 2%. I also suspect that the car warms up slightly faster, but that's likely to be a biased observation.

It's also slightly more frugal - distilled water is only $1/gallon. I'll mix up a big batch and do a few different vehicles at the same time.

I've never had a problem with freezing; Pittsburgh can get pretty cold, but it hasn't been a problem. IIRC 66/33 is good down to about 0degF absolute temp.

[monty23psk]

I am in South Florida and never really get cold days. I use 50/50 mix with BMW blue coolant and the correct amount of WW and never have any cooling issues. Going by temp gauge, it runs cooler since I started to use WW.

[Nick_318is]

Sorry to continue the coolant hijack, but I like the BMW blue mixed 50/50 with distilled water and water wetter. The car never budges from half way, even when driven hard on a track.