Overheating Stroker m20 -solved-

[downforce22]

Last week as I drove home from work, my stroker motor started overheating. It was overflowing as I pulled into the driveway. It had done it once before and I hadn't replaced the thermostat so I parked it and ordered a new low temp thermostat 71 C. I received the thermostat and replaced it last night and it is still overheating. At idle it creeps up to 210 F and starts boiling. Upper radiator hose is very hot and lower is cool to the touch.

Some information on the engine. It has done ~2500 miles and usually was running 190 to 200 F before this started happening.

m20b31
m54b30 crank
86mm bore
Ottoco MLS 86mm headgasket
Waterpump replaced ~2500 miles ago during engine rebuild
Fan Clutch replaced ~500 miles ago
WP Belt replaced same time as fan clutch
swapped from early cooling system to later style including belts, metal coolant hose and reservoir
Running whodwho ms2/laptop to measure water temp
oil is brown not milky
new gallon 50/50 prediluted coolant topped off in reservoir
Radiator return line functions, it was recycling water vapor back to the reservoir

The reservoir was full and I was bleeding the system until coolant came out the bleeder for about 10 minutes while the car was idling. I have narrowed down the possible issues to the following:

1. Failed T-stat - closed when it should be open
2. Air in system/ system not pressurized
3. Clogged radiator/coolant line/ coolant passage
4. Broken water pump not cycling coolant properly

What do you guys think? I am leaning toward a blockage in one of the hoses or failed t-stat. I may just remove the thermostat altogether to determine that it is not the issue and see if that helps.

[validius]

Boil the T-Stat and see if it opens

[BMWManiac]

Coolant is brown? When was the last time you flushed the radiator? I think you need to check your pump, t-stat, and radiator.

If your engine overheated, then you probably cracked your head.

[downforce22]

Coolant is brown? When was the last time you flushed the radiator? I think you need to check your pump, t-stat, and radiator.

If your engine overheated, then you probably cracked your head.

oops I meant oil is brown

[BMWManiac]

Yeah, that makes a difference!

Pull the radiator and make sure it flushes out. While you're doing that, pull the t-stat and put it in boiling water to make sure it will expand. I doubt your water pump is the problem since it is brand new and works off your main engine belt

Also, when bleeding, lift the front up as much as possible when you bleed....heater on full blast too

[downforce22]

Ok so before I bled the coolant system I decided to get it up to temp again to see if a bleed would fix the problem.

I got the car idling and temp creeped up to ~190 at idle. Then I decided to feel coolant hoses. Thermostat was closed so the metal line was cold. Upper radiator hose warm warm. The other two coolant hoses were hot. New coolant was not yet boiling so thats good.

Then I touched the heater hoses at the firewall. Bottom one was warm, not hot, top one was cold. So I cranked the heat, but it only blew cold air. I adjusted the temp adjustment in the car to make sure it wasn't stuck closed or something. I then proceeded to bleed the system with the bleed screw until coolant was dribbling out. The system was still blowing cold air out the vents even on full hot. I replaced the heater valve with a brand new one within the last 6 months and I can still hear it actuating when turning to cold.

Lower cooant hose to heater, still warm, top one still cold.

I have narrowed it down to the following. If the thermostat was bad before, it has been replaced and probably is working, that may have been working the whole time. Either way, this should not affect the lack of hot air coming out of the vents. The possibilities:

Air in the system - This is very possible
Blockage in the system - Possible to prevent water from circulating
Water pump not moving water - Possible, would explain cold air, cold heater lines at firewall, but a dribble of coolant comes out the bleed valve so I am thinking this is not likely

Any combination of the above.

I have drained and replaced the radiator fluid, but I have not drained the block. Before I drained the block to try to find a blockage, I wanted to see if anybody else had any ideas?

Thank guys, this is frustrating since it was fine just 2 weeks ago.

[BMWManiac]

Remove the radiator and let it drain. Now might be a good time to drain the block as well. Take your radiator and run a rose to it and
Ake sure it flows out. When you verify it is good, reinstall. Grab some distilled water and fill the system with just distilled water. Bleed it as normal up to operating temp. Drain, and see how much junk comes out. I do this once or twice depending on the vehicle I work on. Are you using the blue BMW coolant and 50/50 with distilled water?

[nando]

71c T-stat is too damn cold. a cold T-stat is not a solution to a hot engine - all it will do is make your engine run less efficiently. 80c should be the minimum IMO.

how old is the radiator?

[Mthrizzle]

You have a failing head gasket -- hate to state this..but we always hope its the monor stuff

[nando]

he should still get heat in the cabin if the HG was bad.

[Wanganstyle]

You have a failing head gasket -- hate to state this..but we always hope its the monor stuff

perhaps yes, perhaps no - a leak down test would tell.

OP; leak it down if you suspect a HG failure.

run car with no thermostat and see if it will make both radiator hoses hot. its easy enough to remove

[downforce22]

Thanks for all of the feedback guys, I appreciate it.

So I decided it would make sense to drain the coolant and try to find a blockage in the system. I drained the radiator, removed it, then drained the block. There was some sediment in both the radiator and the block. I ran a hose and water through the radiator to flush out any remaining sediment.

Then I ran a hose through the block. I also disconnected the heater core lines and flushed both of them out. With the water inlet at the upper thermostat connection water flowed through the heater core, cylinder head and out the top line.

I topped the system off with water this time to test it out. I reinstalled the radiator and hoses. With the reservoir full, I checked the oil (still nice oily gold/brown, no milkshake color). Make sure there were no leaks and fired it up. Again it crept up to 200 F with no heat coming out the heater. The heater core hoses were cool to the touch, but the bottom one got warmer as I followed it closer to the cylinder head.

This isn't making sense after I flushed the system and it seemed to flow well with the garden hose/water. To make sense of this I found a diagram below with a normal water cycle.



So looking at the diagram (tell me if I made a mistake), we can ignore the hose to the radiator right now since the thermostat is the least of my worries. I ignored the throttle body hoses as they shouldn't affect the process. Now, I thought maybe there is a blockage in the head or block that is preventing water from flowing to the heater core. So with the engine still hot, I disconnected hose 3. The almost boiling hot water in the head came pouring out. To make sure there wasn't a blockage upstream somewhere, I opened the exp tank and stuck the garden hose in there. Water flowed just fine out the hose from the back of the cylinder head. :???: So there is no blockage upstream of the heater core. Also, the lines were filled with water through the exp tank so tells me the left half of the 3 way hose is not clogged.

Im going to check the 3 way hose next to make sure it is not clogged. Otherwise, what could it be??

[Mthrizzle]

Get an infra-red thermometer -- measure the temp of the lower and upper portion of the radiator - report

[downforce22]

well guys, I am stumped. I removed the water pump and the pump seems fine. It spins at the same rate as the pulley.

I am still not getting heat in the cabin. If I pull off the lower cabin hose from the cylinder head if drains and then nothing. So If I open the expansion tank, a vacuum is relieved and the lower hose drains. Any telltale signs the pump is bad? I would rather not replace with oem $150 BMW pump only to find no change. I also tested the thermostat and it open at ~180 F just fine but the car was creeping up to 196 at idle.

[EyExR]

I would do a leak down test at this point.

You may have a couple of issues going on. What caused the car to overheat in the first place? Double check your fan clutch strength to see if that may have started the problem.
Also, bleed the heck out of it. Elevate the front on jacks, cabin air on hot and high, squeeze hoses (especially the bottom radiator hose) and keep bleeding.