White Sludge in Thermostat Housing, Rust in Coolant Passages

[///M3RIC]

I have an M3 that hasn't been driven in ~10 years. I've been slowly tearing it down for repairs and maintenance. I removed the thermostat housing and waterpump and found white buildup in the housing and pump and rust in the coolant passages.

Does the sludge indicate I need to replace the head gasket, or could that be caused by something else? When I dropped the oil pan to do the rod bearings the oil wasn't milky. When I drained the coolant, it came out clean.

Rust in the passages could indicate incorrect coolant, tap water, something else? Can the rust be flushed out? Or is this block cooked?

[Slideways]

Someone used tap water to top off the system or refilled it with tap water + coolant mix the last time it had a coolant change. After sitting for 10 years with that in it, it formed mineral deposits and some rust in the iron block. BMW coolant + distilled water, even if not changed for 10 years, will not do that.

Flushing the system a few times with water is probably the best option. Remove the coolant drain plug from the block, if you have not already, to get all the old coolant out.

S54 headgaskets like to break between cylinders, so unlikely it is a headgasket.

[Keith_MN]

Check out a product called Thermocure. A few people here have used it, myself included. I had some nasty corrosion in mine. Replaced or thoroughly cleaned most everything except a few difficult to access pieces, flushed it a few times, did a Thermocure treatment and it seems to be happy now.

Edit. Also you might want to invest in an ultrasonic parts cleaner.

[6speedS54]

I just did Thermocure treatment on my cooling system, had rust also. Prepare for 3-4 days of driving around with it in your system and then full day of flushing it out. For the thermostat manifold, do a mix of 50-50 vinegar/water, let sit for 30 min or so and scrub it out with plastic scraper.

[///M3RIC]

Thanks for the input, it’s relieving to hear I’m not the only one that has experienced this. I’ll definitely get some Thermocure and flush the system.

[///M3RIC]

Someone used tap water to top off the system or refilled it with tap water + coolant mix the last time it had a coolant change. After sitting for 10 years with that in it, it formed mineral deposits and some rust in the iron block. BMW coolant + distilled water, even if not changed for 10 years, will not do that.

Flushing the system a few times with water is probably the best option. Remove the coolant drain plug from the block, if you have not already, to get all the old coolant out.

S54 headgaskets like to break between cylinders, so unlikely it is a headgasket.

So you think the white sludge is mineral build up? That would make sense, my mind went to worst case scenario and thought the head gasket was a goner.

[6speedS54]

Here are some pics

[SteelGreyM]

The rust is from tap water. Hope that sludge isn't head gasket sealant

[///M3RIC]

Here are some pics

You had the white sludge too! Was it mineral build up? No head gasket issues?

[6speedS54]

You had the white sludge too! Was it mineral build up? No head gasket issues?

yeah, mineral buildup from tap water, no head gasket issues that I know of. Car has 124K miles on it. Chances are radiator has build up also, will replace it later on. If you do Thermocure, prepare for a not so pleasant smell 😂 (wet dog, sewer kinda during it being in the cooling system and couple weeks post, don't forget to make sure it cycles thru the heater also)