520i E34 M20 fan only blows hot above 2k revs help

[520Ichester]

My 520i E34 M20 1988 is only blowing hot air internally when the revs are above 2k. At idling the fan blows cold but the engine get hotter. Also the temperature gauge goes to 1/2 within 5 minutes at idle and when I rev to 2k the temperature drops very quickly to 1/4. I would guess it is one of the water pumps or possibly an air block. Does anyone have any ideas? The car is fine when driving but very scary when in a traffic jam. :(

[netmgr]

same engine here, my points..

temp up to half after 5 mins of idle...yep sounds ok same as mine depending on how hot the day is..
the internal heater matrix gets its heat from the coolent in the engine...so relys on the pump to pump it all round...the pump works on engine speed...but i cant think of a reason why idle isnt enought speed to pump round the engine but 2k is...after all if the pump works at 2k i see no reason it wont work at 800.ide speed

also no matter how fast the pumps going the m20 engine shouldnt ever fall below half way on the temp scale unless its just been started.

there is only one pump...so id guess thats playing up..when was it last changed as it is a service part...ie ur supposed to change it every so many miles reguardless of if its broke..because basically it will do eventually

but see what everyone else says

[Bill R.]

fraction above or below, if yours is cooling down when the rpms are held at 2k then you have a bad thermostat thats sticking open which would also contribute to the poor heater performance. Also if the heater is cool until 2k rpm you could have a bad auxillary coolant pump which is mounted on the firewall below the heater control valves and helps to circulate more hot coolant to the heater core when idling or at low speeds... First thing I would do is replace the thermostat so that the engine temp is always right at halfway on the guage.






My 520i E34 M20 1988 is only blowing hot air internally when the revs are above 2k. At idling the fan blows cold but the engine get hotter. Also the temperature gauge goes to 1/2 within 5 minutes at idle and when I rev to 2k the temperature drops very quickly to 1/4. I would guess it is one of the water pumps or possibly an air block. Does anyone have any ideas? The car is fine when driving but very scary when in a traffic jam. :(

[netmgr]

i wasnt aware the M20 had another pump for the heater..

is this it:

http://www.netmgr.co.uk/b.jpg

is it fitted to cars with no aircon?
how does it kick in?

[632 Regal]

but dont see the electrical connection. All BMWs have an auxillary heater pump for idling. As Bill said replace the thermostat right away so you dont cause un-needed wear.

[Bill R.]

auxillary pumps or not but all the US e34's have them, I can't speak for the euro and other market cars




n
but dont see the electrical connection. All BMWs have an auxillary heater pump for idling. As Bill said replace the thermostat right away so you dont cause un-needed wear.

[E34-520iSE]

Hey 520IChester I have the same car & engine as you. I don't have the extra water pump on the heater valves either, but I don't have any cooling problems. When I first built my engine it would constantly overheat in traffic, standing etc. and that's after changing the thermostat, viscous fan clutch, heater valves, and obviously the water pump and head gasket were replaced in the engine build. It turned out to be poor bleeding! The heater matrix and it's "send & return" pipes are a BIG air bubble trap. The long hose that returns water to the block from the heater matrix should be warm as soon as the thermostat opens. Hope this helps! Shaun

[520Ichester]

I will try bleeding this weekend, Just a few more results of tests that i have done.
If i leave the car idling it goes past 3/4 on the temp gauge. After 10 seconds then of 2k revs the temp is back down to just over 1/4. I was going to take off the water pump and check for any damage?. Any help

[E34-520iSE]

I will try bleeding this weekend, Just a few more results of tests that i have done.
If i leave the car idling it goes past 3/4 on the temp gauge. After 10 seconds then of 2k revs the temp is back down to just over 1/4. I was going to take off the water pump and check for any damage?. Any help

Might be a good idea to check the pump before continuing, especially if you don't know how old it is. Check the thermostat too. I found that drilling a small hole in the thermostat helps when bleeding. I discovered a quick and effective way of bleeding my system, but I know it upsets some people. It's the "compress the system with your mouth" trick - you've got to be aware that antifreeze is poisonous so be very careful.

Hope you get it sorted!

Shaun

[520Ichester]

Just to let you know the outcome of the above issue, I replaced the thermostat and bleeded on ramps and all was fine. I had noticed that the muppet before me had manually sealed the bleed screw on the radiator, so i replaced with new. All is working as normal, Thanks for all the help ;-)