New here. M42 Overheating

[Aufbau Principle]

Posted on r3v as well.

Hey all, brought home a '91 318iS a few days ago. Car ran fine when I test drove it a few days prior to that, but on the way home, the temp gauge climbed into the red. Let it cool off for a bit, then kept going, but blew the upper heater hose that goes from the firewall into the engine block.

Replaced that, but the car still overheats within about 15 minutes of idling, less when driving it slowly around the block.

There's no heat out of the vents with the heat knob turned all the way up. Fan doesn't seem to blow either when turned all the way up, all vents open, all sliders to the right.

Upper and lower radiator hoses don't feel like there's any pressure in them. Doesn't seem to be leaking anywhere else.

Checked the oil cap and dipstick for milkshake, oil's dirty but otherwise fine. No white smoke out the exhaust.

Car starts up, idles, and drives just fine, I shut it off when the temp gauge climbs past the 3/4 mark.

What are the possible culprits? Busted water pump, busted thermostat, clogged hose somewhere, clogged heater core/valve/radiator? Shitty bleed job?

Lower radiator hose on the driver side appears to be leaking now.

Car also smells rich on startup, and has slight idle fluctuation. Fuel pump sounds kind of loud, can hear it buzzing from outside the car.

[Tgoode318]

Sounds like you have multiple problems. The Fuel Pump and the idle fluctuation are probably unrelated problems but should also be taken care of.  Your slight idle fluctuation is probably from small cracks in the rubber breather hoses resulting in un-metered air entering the system. Try spraying carb or brake cleaner around in the engine and listen for the engine to rev. if you hear the revs go up then you have a crack in the hose. As Far as your cooling system is concerned Be very careful and mindful of the temp. If you see it getting to hot shut the engine off immediately/pull over / get a tow as overheating is one of the number one way's to destroy an engine.  To find out whats wrong with your cooling system i would start with the basics and go from there. First make sure your hoses are in Good Condition/not leaking and are also seated and connected properly.  Then make sure your aux fan and engine driven fan are working.. If you dont have a good recorded service history on when the last cooling flush was i would drain all coolant from the block and rad. And Replace with only GENUINE bmw Coolant.  When you put in the coolant make sure you mix it properly with DISTILLED water. If you use tap water, mineral clogging build up could occur.  Before you refill with coolant you should check your thermostat under the thermostat housing as well It could be clogged and not opening. If it were me i would go ahead and replace this while i was at it. After you refill the coolant "Bleed the system" Of all air bubbles, an improperly bleed system can cause over heating. Make sure your radiator cap is put on properly as well as a damaged cap or bad seal/improperly put on cap can also cause over heating. After that i would then run the car and monitor the fluid levels very carefully. If you see alot of fluid Loss you probably have a leak in the system some where. If all those things check out but you still have over heating it could point to a more serious problem like bad water pump bad head gasket or even a warped or cracked head.  Also do you know how to do the stomp test for error codes? Do this test and see if you have any fault codes stored in the computer as this can help you diagnose the cars problem's easier. Good luck!

[Aufbau Principle]

Car's not going any further than a few hundred feet from my house until this gets solved. I "newspaper tested" the clutch fan, seems good. Is the aux fan the one that's visible through the lower front valence? I don't think that works, but the a/c compressor doesn't have the belt on it, if that matters. Tried bleeding the system with the nose jacked up, no bubbles or fluid comes out of the bleeder screw. There is no fluid going through either of the upper radiator hoses. Is this indicative of a busted water pump or thermostat?

Stomp test showed code 1252, some problem with fuel injectors.

[Tgoode318]

You need to keep pouring fluid in the expansion tank until fluid and air bubbles come out of the top of the tank when you see air bubbles keep pouring (coolant will run down the tank while bleeding) once no more bubbles come from the bleed screw your done. the water pump just circulates coolant so even If the pump is bad you should still have a pressure build up in the hoses. If there's no pressure build up after you made sure there is coolant and a thermostat then it would point to bad head gasket or cracked head

[Aufbau Principle]

Does no pressure in either of the hoses going to the thermostat housing indicates a closed thermostat? Is it worth trying to bleed again, or should I just get to pulling the thermostat?

[DesktopDave]

I'd drain the system and do a cooling system pressure check. Rent or buy a coolant pressure tester with threaded adapters. In a pinch you can use a GM cap and a barb fitting if you seal the bleed passage with RTV. The system and cap must hold 2bar pressure in order for the cooling system to work. Any leaks, and the car will not bleed properly. The pump, radiator and expansion tank are more troublesome to test. I tend to consider those as wear items with a ~100K mile life, given the high pressure of the modern BMW cooling systems. IMHO the older 1 Bar cooling systems were far more robust, I wish BMW still used them. I love progress, but risking an engine to save 5% of vehicle weight is idiotic. How many DOHC BMWs have gotten scrapped due to chronic overheating & warped heads?

I'd also be tempted to get a leak-down or compression test done on the motor. I'd expect to see around 200psi on a healthy higher-mileage motor. IIRC 230psi is BMW spec for a new motor. I know that it's annoying to get these tests done, but without a good baseline you'll just be tossing parts at the car.

[lars318is]

I had the same problem, and it turned out to be the thermostat. After you fill and bleed the system, check your radiator hoses. If either of them are still cool when the engine has warmed up, then it is your thermostat.

[deansweet]

thermostat installed backwards?