Firstfives.org

Morning guys,

Last night my 75' 530i developed an interesting problem. Exterior temp last night was roughly 65 degrees Fahrenheit. The car was running fine till i drove it home last night. Got off the freeway, took the off ramp a lil hard, and then the temperature shot up quickly. (usually sits below the line towards blue side) it shot up towards the line towards the red and i quickly pulled over before it got past the red. Open the hood and the engine is somewhat cold. Intake manifold was cold. Valve cover was warm but not hot. upper radiator hose is hot however, but lower radiator hose is stone cold. This makes believe there is a blockage in flow of coolant or no coolant flow all together. From what i can recall i know on E36 cars, the coolant flow from the top of the radiator hose, through the radiator, and back to the engine from the lower radiator hose. i looked on the technical FAQ here and on the coolant link, the M30 has its coolant flow from the lower radiator hose, through the radiator, and back to the head from the upper radiator house. So.... im a bit confused now. Itll make sense if it flows from top to bottom since the top hose is hot right now. But on this website it says it flows from bottom. Another thing i noticed was that the radiator itself was hot on the upper radiator hose side and warm on the lower radiator hose side.

Heres the link...
http://www.firstfives.org/faq/cool/cool.html

It coolant does flow from top radiator hose to bottom, im guessing either a stuck thermostat or a clogged radiator. I opened the bleed screw and is water coming out but more of a dribble then a stream. I still get cabin heat so im guessing the water pump is working for that. I recently had my radiator rodded out and cleaned from a reputable shop so i'm hoping thats not my problem. Though I also changed the thermostat recently so hoping its not that as well. I guess the only way to tell is take it out and test it.

Since i was a a 3 miles away from my house i waited for the engine to cool and drove it home. the needle never got past the middle of the temp gauge, even while being stuck at a red light for a while. easiest case would be air trapped in the system and it just got itself out wen i open the bleed valve.

any other ideas?

Check the easy stuff like the thermostat first. I replaced mine as a preventive thing back when I got my current 528i and I had multiple failures with the replacement tstats... should have just left it alone!

I guess that's the quickest way to start, stick it in some hot water and see what happens. Next I would check the radiator...

Let me know what you find!

Water pump ?
Can you see strong circulation in the expansion tank ?

Given that you said the engine was cold, but you had heat, it suggests it was bled properly since water was circulating, and it wasn't overheating. Which suggests to me you have a gauge problem, not a cooling problem. Check all grounds, perhaps adding one and check the sending unit connection.