Hey fellas,
I've been fighting air in my cooling system for years. It's bad enough that I have to stop every 10-20mi to bleed it out, or I'll end up with a massive air pocket in the thermostat housing that will cause my temp gauges to peg and eventually puke coolant out of the expansion tank overflow line.
The most obvious cause was a bad HG or cracked head/block that was allowing combustion gases to get in to the cooling system. However after checking for both hydrocarbons and acidification multiple times, I'm confident that this is not the cause. Fast forward after many, many sleepless nights and I think I may have found a cause.
The thermostat housing sits roughly 2" higher than the top of the radiator (e28 535i) and at the same height as the cap on the expansion tank. However the fluid level in the tank is 2" below the cap. So while the fluid level is at the same height as the top of the radiator, it's actually 2" lower than the thermostat housing. I can bleed the thermo housing by lifting up the tank and cracking the bleed screw, but once I drive the car and the water pump circulates and it heats/cools the fluid in the system, inevitably those fluid levels will equalize and I'll have 2" worth of air gap in my thermostat housing. That's my working theory.
I'm running the stock late model m20 expansion tank, which a quick Google image search show is the same tank being used on ~90% of the M30 swaps I can see. I see some swaps using the M30 expansion tank that mounts to the firewall, but due to the location of a bunch of relays and the strut bar, I don't have room. (side note: our LeMons/ChumpCar E30 has an M30B35 in an identical installation, except it runs the M30 expansion tank. It's never had a single cooling issue).
So I need some detailed info and photos from you M30 guys:
- What expansion tank are you running? M20 (early or late model) or M30?
- Does your thermostat housing sit above your radiator? By how much? What radiator are you using?
- How high is your thermostat housing compared to the fluid level in your expansion tank?
I know I can't lower the front of the engine as there's only 1/8" between my oil pan and the steering rack. And I can't raise the expansion tank more than ~1/4" because the cap will hit the hood. But there must be something I'm missing... Help!
(pics to come later today)
I've been fighting air in my cooling system for years. It's bad enough that I have to stop every 10-20mi to bleed it out, or I'll end up with a massive air pocket in the thermostat housing that will cause my temp gauges to peg and eventually puke coolant out of the expansion tank overflow line.
The most obvious cause was a bad HG or cracked head/block that was allowing combustion gases to get in to the cooling system. However after checking for both hydrocarbons and acidification multiple times, I'm confident that this is not the cause. Fast forward after many, many sleepless nights and I think I may have found a cause.
The thermostat housing sits roughly 2" higher than the top of the radiator (e28 535i) and at the same height as the cap on the expansion tank. However the fluid level in the tank is 2" below the cap. So while the fluid level is at the same height as the top of the radiator, it's actually 2" lower than the thermostat housing. I can bleed the thermo housing by lifting up the tank and cracking the bleed screw, but once I drive the car and the water pump circulates and it heats/cools the fluid in the system, inevitably those fluid levels will equalize and I'll have 2" worth of air gap in my thermostat housing. That's my working theory.
I'm running the stock late model m20 expansion tank, which a quick Google image search show is the same tank being used on ~90% of the M30 swaps I can see. I see some swaps using the M30 expansion tank that mounts to the firewall, but due to the location of a bunch of relays and the strut bar, I don't have room. (side note: our LeMons/ChumpCar E30 has an M30B35 in an identical installation, except it runs the M30 expansion tank. It's never had a single cooling issue).
So I need some detailed info and photos from you M30 guys:
- What expansion tank are you running? M20 (early or late model) or M30?
- Does your thermostat housing sit above your radiator? By how much? What radiator are you using?
- How high is your thermostat housing compared to the fluid level in your expansion tank?
I know I can't lower the front of the engine as there's only 1/8" between my oil pan and the steering rack. And I can't raise the expansion tank more than ~1/4" because the cap will hit the hood. But there must be something I'm missing... Help!
(pics to come later today)
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