coolant plug on m42

[The_Nietzschean]

Hi all,

I have an overheating problem that I cannot figure out.
My car is a 1991 318i with the M42 engine.
The first time I took it on the highway it started overheating once I reached 70mph.
Since then it has progressively gotten worse. Now I can't even go a mile before the engine is in the red.
I flushed the coolant (properly, thanks to the e36 bentley manual). Checked the themostat by feeling the upper radiator hose and its nice and hot to the touch after the engine has been running.
The temperature switch for the axillary fan is defiantly broken and I am "bypassing" it right now by having the air conditioner on (the little snowflake button on the dash pressed in.)
I'm trying to ID what the problem is.
A few things:
1.) Whether I turn on the heat or the air conditioner, the air that comes out is always the same temperature, which is about the ambient temp. Could this be a symptom of my overheating problem or is it a separate issue entirely?
2.) The radiator only gets hot on the side that is close to the reservoir cap. Is that normal?
3.) The lower hose, leading from left side of the radiator to the thermostat housing, stays cool. Could this indicate a block.

I just bought this car and it was fine until I took it on the highway a few days ago. I need it for work so any help would be greatly appreciated.

[The_Nietzschean]

sorry for the novel first post.
any suggestions for the "noobie"

[tonywonder]

make sure hoses 1,2,4,23 and 22 are connected properly and not pinched. hoses 22 and 23 attach to your hvac system at the firewall next to the brake booster (driver side). check for leaks. make sure you properly bleed the system of any air by using the bleeder screw and putting the car at an incline. hose number 1 and 4 are typically the hotter hoses. atleast in my car they are. hose 4 as u can see attaches to the pipe on the block. you described the lower hose to attach to the thermostat housing but maybe im confusing your point of reference.

also go to www.m42club.com it has more specific info on the m42.

ill check back later. to see if you have solved your issue.

[BlueBMW]

Come on over to M42club, we'll help you out :D

[Matt-B]

m42club.com

and maybe its possible radiator is clogged?

[The_Nietzschean]

thanks for all the invites to m42club.com. I tried to join that site but it rejected my email because it was a gmail account. Which ones do you use?
I am going to re flush the coolant system today.
tonywonder: I will check those hoses. thanks for the diagram. Where did you get it?
Matt-B: I thought it may be that as well but I have no idea how to check for a clogged passage. Is there a simple test which doesn't involve taking the whole thing apart?

Thanks I post more later on the progress or lack thereof.

[The_Nietzschean]

Tonywonder: when I mentioned the lower hose I meant hose 2. I haven't checked 4 yet. I will after this coolant flush.

[BlueBMW]

m42club blocked free emails because of too much spam. If you have an email through school, work or your isp it should work fine.

[The_Nietzschean]

Strange developments.
I bled the coolant (several times actually) and think I have purged all the air from the system.
The radiator is at the KALT mark.
I have the snowflake button on to artificially turn on the auxiliary fan as the switch is broken.
When I do drive, I have the heater on full.
When I drive around it will eventually overheat. The strange thing is that when I park it and give if 4.5K revs it drops the temperature almost immediately. Why would this be?
Also, the lower radiator hose (hose 2 in the above diagram) was hot near the engine and cool near the base, where it meets the radiator. Does this mean it is clogged? I massaged and squeezed it while the car was running and the heat slowly moved down the tube. I think I should take it out and expect to find a clog. But could someone explain why the car idles/low revs at such a high temperature and why reving the engine brings it down?

[Simon S]

The strange thing is that when I park it and give if 4.5K revs it drops the temperature almost immediately. Why would this be?
Also, the lower radiator hose (hose 2 in the above diagram) was hot near the engine and cool near the base, where it meets the radiator.

These symptoms lead me to believe that circulation is spotty - hence, water pump may be due for replacement. It is a wear item.

[The_Nietzschean]

Simon - I think you are right. I didn't want to believe it but it is the only part left.

Where is the best place to buy one of these?

[Matt-B]

BMAparts.com

Pelicanparts.com

Rockauto.com


MAKE DAMN SURE you get one with a metal impeller

[KenC]

All of the symptoms you've described indicate a thermostat that is stuck closed. That's your blockage. You're essentially running without a radiator. You can't bleed a cooling system when the thermostat is closed either.
Your lower radiator hose is hot near the block because your head is heating it up.

Take the lower hose off at the radiator and dump the coolant out, if there is any. Hook it back up and wait until the temp of the car gets to like 3/4 on the gauge (well above where the thermostat should open). Turn the car off and then take the lower hose off at the radiator. It it's not FULL of coolant, then your thermostat isn't opening.


There's also a SLIGHT chance that you have a massive air bubble.

[tonywonder]

my first would be that the therm is stuck. second would be the pump. regardless it needs to be fixed and if ur going to do that job you might as well replace both. i got the metal impellar waterpump and the wahler 88deg thermostat when i replaced those parts. good luck.

[The_Nietzschean]

The thermostat will eventually open but defiantly beyond the point where it should. I am in the middle of installing a new water pump but have hit a snag. The pulley is stuck on the water pump and refuses to come off. I removed all four bolts but I cannot even pry the thing off with a screwdriver. Rubber mallets and even metal hammers don't work either.

Any suggestions?