E30 M30 overheating issue

[USMarineRetired]

I have read everything I can find related to overheating in an E30, E24, E28 and E34 and I cannot find an answer. I'll make this as brief as possible.

Originally thought it was a thermostat. Put in water and boiled it until it opened. Open temp was right on the money. Good Thermostat. Thought possibility of the water pump. Not leaking but wife works at parts store so I installed a new water pump thinking the old one sheared off the impeller. I had no coolant flow, it seemed. Bypassed the heater core, still no coolant flow. Hooked heater core back up. Radiator was staying cold in the lower half. I replaced the radiator thinking it was clogged. (I purchased this car from my sons friend who stated he ran some of that radiator seal in it, so I thought it might be plugged with that stuff.

Ok, so New radiator, New Water Pump, Heater core good, Thermostat good. Car is elevated more than 2 inches above rear. I have bled the system may times but still wants to overheat and boil back into expansion tank. I cleaned out the tube on the expansion tank that goes to the radiator as I found that to be clogged. Still wants to overheat.

Last night I grabbed the garden hose and turned it on to flow about 1.5-2.0 gallons per hour. Very light flow. I removed the main hose from the bottom of the expansion tank and inserted the running garden hose into the rubber hose that leads to the thermostat housing area and "T's" back to the upper connection of the heater core. I started the car and everything worked properly. I got heat. I have flow back through the radiator and into the expansion tank via the 1/4 inch hose. I let it run for 30 minutes with no issue at all. Set up like that, the cooling system seems perfect.

Now knowing that the system has no air in it, I left the car running, filled up the expansion tank and removed the garden hose from the hose that was attached to the expansion tank and quickly returned it to the expansion tank.Right after that the heater started blowing cold again and the car wanted to overheat.

I have a new expansion tank and cap coming in from Pelican early next week. If it's not that, which doesn't seem likely to me, I don't know what the issue is.

My compression readings were 175-180 across all 6 cylinders. All 6 plugs looked the same.

I usually don't need guidance but I am seriously at a loss for ideas on this one. Any help would be GREATLY appreciated.

Thank you,
Tony

[Kershaw]

How's your fan clutch? Of course, that wouldn't explain why it goes to cold.

[glnr13]

is your thermostat facing the correct direction?

[ThatOneEuroE30]

How do you have your cooling system routed? It is possibly it is routed wrong and causing it. If thats the case the reason it was fine with the hose connected is because it was flowing more and adding to the system. It going to take the path pf least resistance and the hose hooked up could be forcing it to run correctly with the added pressure to the system.

[LowR3V'in]

i guess it's backwards thermostat

[Bearmw]

Sounds like the tstat to me too. Among the many tricks I like to do includes drilling a small 1/8" or so bleed hole on mine whenever a new one is going in to make things easier. Raising the overflow reservoir also helps somewhat with bleeding. I also find that blowing in the overflow hose to slightly pressurize the radiator helps a lot with this.

Good luck.

[NZM3]

Hi,
I think from what you described you have a blockage in the return system/small hose from L/F of the cylinder head to the top of the expansion tank.

Water should be returning from the head to the expansion tank when the engine is running you should see this with the radiator cap removed.

oops, just read that you have 6 plugs, this is for the 4 cylinder M3 still it may be of some use to you.
.
Usually find corroded and blocked up fitting to the cylinder head.

[USMarineRetired]

Thank you all for the replies. It’s been a crazy couple of weeks. The overheating turned out to be air. I thought for sure I had it all out. I ended up squeezing/massaging to crap out of the upper radiator hose I felt the heater start kicking out heat.

I have never had a struggle with an air-pocket until I got a BMW! Ha!

Thanks again for all the input and I apologize for the delay.

Tony

[ThatOneEuroE30]

Thank you all for the replies. It’s been a crazy couple of weeks. The overheating turned out to be air. I thought for sure I had it all out. I ended up squeezing/massaging to crap out of the upper radiator hose I felt the heater start kicking out heat.



I have never had a struggle with an air-pocket until I got a BMW! Ha!



Thanks again for all the input and I apologize for the delay.



Tony

These m30 engines are notoriously difficult to get all the air worked out. I spent close to 4 hours getting mine bled.

[USMarineRetired]

Sounds about right with the 4 hours timeframe. That was about my total time I spent trying to fix it.

On a side note, that if you noted the “Kiss my ass” in my signature line, my apologies. I did not insert that in my signature line. I never have and never would say it or write it unless someone warrants the phrase. Must have happened during the approval of my first post. Regardless, it’s gone now.

[Echo30V]

Same here, took me a few hours to bleed the system on ,my 1990 325i Vert. Out of the e30, e36 and e46, the e30 was the most difficult to purge of all the air.

[ForcedFirebird]

Pics of the engine bay? I see a lot of m30 swaps trapping air due to the expansion tank height. The cap needs to be the highest point in the system.

Same here, took me a few hours to bleed the system on ,my 1990 325i Vert. Out of the e30, e36 and e46, the e30 was the most difficult to purge of all the air.

I have never had any of the bleeding issues people discuss, and I have filled countless e30 cooling systems over the years. Since you have a late model, it's simple to pop the expansion tank out of the holder and elevate it while filling if it gives you issues, but the only time I have had to do that was when the car was perked on a steep decline. Simply take the cap off, open the bleeder and fill until you have a steady stream from it. Close the bleeder, finish filling the system. If the expansion tank is the highest point, you will slowly see bubbles coming up so keep topping it off (can massage the hoses to speed it up). Once full, start the car with the cap off and warm it up for the t-stat to open, top off if necessary.

If you have trouble with bleeding, check the small hose that goes from the radiator to the expansion tank. Can't tell you how many times I've seen that clogged and causes overheating/bleeding issues.

[USMarineRetired]

If you were asking me for an engine bay photo, I don’t have one in my phone. I can take one over the weekend. My expansion tank is the highest in the engine compartment.

I have serviced the cooling system once before and it went as advertised. This past time gave me an issue. Not sure why. I think the air pocket was in my heater core to begin with. I had no issues with cooling and heater output until I turned the heater on for the first time. All is well now.

[Echo30V]

Forced: Thanks, thats exactly what I did, had car elevated, checked the small hose, but the trapped air was extremely stubborn and only reluctantly yielded.