twistednut's foolproof coolant refill procedure

[Ryann]

We've all read about it, talked about it, and struggled with it. The m42 is "a bitch to bleed". The following ridiculously easy procedure was shown to me by twistednut here on the forum and has worked flawlessly for both my own and my father-in-law's m42 powered e30s as well as an e46 330i. Mix yourself up 7qts. of coolant, open your heater valve, and:


1. Remove the hose clamp that holds the upper radiator hose onto the thermostat housing and pour coolant into the upper radiator hose until the coolant reservoir is at the cold fill line, then put the hose back on and tighten the clamp.

2. Remove the hose clamp that holds the upper radiator hose onto the radiator and pour the remaining coolant into the upper radiator hose, then put the hose back on and tighten the clamp.

DONE.

[bernzpeed]

what?

[Ryann]

Yup.

[Dj Buttchug]

win!

[Jafxod]

Guessing this would work for an m50 with m42 rad?

[///digitalme]

i did that on my m42 thats what the guys from mesa performance told me to do..still didnt work for me...thermostat is next on the line

[AndrewBird]

It took Josh and I LITERALLY 1 try and about 10 minutes to bleed his M50 swap with an M42 radiator. I honestly don't know how people can't do correctly.

My procedure for any car is fill the system with coolant through the radiator cap/expansion tank until full. Then, start the engine and continue to fill until full once again. Wait for the engine to full warm up and the thermostat to open. You can tell my feeling the radiator house coming from the thermostat housing; it will be warm once the thermostat has opened. Once open, refill again and put radiator cap on. Then after a few days, when the engine is cold, I recheck the level and refill if needed. Never had a problem on numerous different cars doing it this way.

One thing to note that I'm not sure if it even matter or not, but is good practice, is to poor the coolant in slowly. Too fast and you can actually introduce air into the system.

[ReallyDirtyThirty]

Fill expansion tank with coolant, raise front end of car (can be accomplished by pulling up on a curb, open hood, remove cap from coolant tank, blast heat, rev the piss out of the motor.

This method has always worked extremely well for me...

[Ryann]

i did that on my m42 thats what the guys from mesa performance told me to do..still didnt work for me...thermostat is next on the line

You mean you're still having engine temp. issues at idle, but not because you've got air in the system.

My procedure for any car is fill the system with coolant through the radiator cap/expansion tank until full. Then, start the engine and continue to fill until full once again. Wait for the engine to full warm up and the thermostat to open.

The problem is that sometimes there isn't enough hot coolant behind the thermostat to cause it to open.

One thing to note that I'm not sure if it even matter or not, but is good practice, is to poor the coolant in slowly. Too fast and you can actually introduce air into the system.

I totally agree, and this applies to the above method as well imo.

[///digitalme]

Yeah I called the place I bought my fan clutch told me this same procedure but still have the problem so im going to replace the thermostat hopefully this weekend and see what happens also will switch to the BMW coolant

[Threehz]

Sorry to revive a dead thread but I'm replacing my water pump and tstat soon for summer.

What makes the normal way to do it hard in the first place?

Ryann, you said sometimes there is not enough hot coolant behind the tstat for it to open. This makes sense, does this prevent coolant from filling up the entire system properly?

[bmwman91]

Here's the real deal with filling the coolant system in the M42. You have to bleed it, end of story. However, the difficulty of that process is largely up to you.

In the thermostat housing, there is a small bypass groove that connects the hot & cold sides. In many cases, it is totally plugged with gasket sealer and mineral deposits. Start by cleaning it out. When you install the thermostat housing with a new gasket, either use NO gasket sealer, or if you do, be really REALLY sparing with it so that it doesn't just squeeze into the bypass groove. If that groove plugs, then bleeding the system requires you to wait until the motor fully warms up and the thermostat opens.

So, with the bypass groove unobstructed, fill the coolant system until it is like 2" from overflowing. You will need to add coolant, let it drain in, fill, drain, etc. Once done, open the bleed screw 1 turn and start the car. Chances are you will hear an ugly screeching/hissing sound. That is all of the remaining air in the system squeezing out of that bypass groove in the thermostat housing. At this point, you are basically done. I usually let the motor warm up a little anyway and revv it to 3000RPM to bleed out the little remaining air, and to get the coolant level down around the fill line. You don't need to bleed off that much since, once the air screeches out, the level in the (previously overfilled) tank drops pretty far.

When bleeding, keep a close eye on the expansion tank. You do not want to run it dry!

[Ryann]

^^Just use Stan's method. It is simple as hell, works perfectly every time, and with minimal use of the bleed screw (if at all).

[reelizmpro]

After weeks of coolant boiling out of the cap, changing parts and using different bleeding methods including only filling the radiator side of the hose but not the thermostat side...I'm happy to report that this method worked the first time I tried it! Wow, I can't believe what a pain it was to bleed this radiator. I may just upgrade to a Z3 radiator on my S52 swap at some point just for the piece of mind. I usually don't bump old threads but this one should be a sticky as there are others who encountered the same problem with air in the system.