f$@#'in overheat

[Rev Engineer]

I thought I was on the home stretch with my winter long s50 -> e30 m3 rebuild and conversion project. I've got it running, but it keeps overheating. I've spent 3-4 hours over the past three days trying to bleed the damn thing. I took the t-stat out and drilled a hole - which seemed to not make any difference. I've had my best luck by reving the motor until it starts to spit some air into the holding tank and then pulling the small radiator to tank hose. Then I usually get a blast of steam out the radiator and then I run water into the reservoir until I get a steady stream out the radiator. I did this a few times (over a period of +45 mins) to the point I was certain all of the air was out. But, then when I go out for a spin, I have to run the aux fan and heater to keep the temp under 3/4 and I limp back home. Could this be because I'm trying to run just water? I've used water in the past without a problem - and then I convert to antifreeze when I know I won't have to take the cooling system apart for awhile.

When it's overheating the radiator does not feel that hot so I'm thinking I'm not getting any flow through it. Could this be one stubborn air pocket or something else? The t-stat, water pump, and e36 radiator are new. The motor was just rebuilt. I ran a compression test to make sure it wasn't a head gasket problem - 200psi on all 6. I've flushed so much water through the radiator and block that I know they're not plugged. I'm sure I have for the heater core hoses on right - bottom to the head and top to the 3-way hose. I'm really not sure what to try next. I might try taking the t-stat out completely (and maybe test it in boiling water), or unbolt the water pump and make sure it’s not damaged. Any other ideas anyone? I also tried jacking the front of the car up.

[Rev Engineer]

I may have complained too soon. I took the car out and drove about 10 miles combination street and freeway and the temp gauge stayed about between half and 3/4. After the drive I left it idling for about 5 mins before it started breaking 3/4. The aux fan brought it back down. I used an infrared point and shoot type temperature sensor and found the t-stat housing to be about 185-190 with the needle between 1/2 and 3/4. At 3/4 the t-stat housing starts to break 200F. I thought I was done until one of my hoses blew off at about 210F. I was lucky I wasn't standing in front of it… I'm guessing I must not have tightened that one down far enough.

Does any one have a clue between the instrument gauge and the t-stat housing temperature? Should they match? 85C is 185F and I think I have a 80C t-stat so this seems to match ok. I’ll need to double check, but maybe the s14 motor uses a 70C t-stat and the s50 is going to normally run high on the instrument cluster gauge with the s14 temp sensor. Has anyone here that’s done an s14 -> s50 conversion know about the temp gauge situation?

[Jason89i]

Has anyone here that’s done an s14 -> s50 conversion know about the temp gauge situation?

with an oe s50/s52 thermostat, the temp gauge will run a little over half on the highway. with an 80deg thermostat, the temp gauge will run right inbetween the 1/4 and 1/2 mark. sounds like yours is running a bit high.

cheers, jason

[Rev Engineer]

Thanks for commenting. Did you use the s14 or s50/s52 temp sensor? It looks like the e30 m3 stock t-stat is 80C. The etk lists 88C and 92C as options for the e36 and the e30 m20. Based on this, it makes sense that the temp gauge will read high on the e30 m3 cluster. A little high with the 88C and even higher with the 92C t-stat.

Did you do anything to correct the tach? It seems that in order to use the e30 m3 cluster, you need to adjust the tach signal before the instrument cluster. Once I get my car running good I'm going to work on building a converter board to adapt the 6-cyl tach signal to the 4-cyl gauge.

[Jason89i]

Did you do anything to correct the tach? It seems that in order to use the e30 m3 cluster, you need to adjust the tach signal before the instrument cluster. Once I get my car running good I'm going to work on building a converter board to adapt the 6-cyl tach signal to the 4-cyl gauge.

just get a 325i coding plug (plugs right into the front of the cluster) andd you wont need to build a converter board. viola tack now reads the 6cyl impulse.....but it will still slightly be off. the m3 vs 325i tach has a different faceplate. at the 4o'clock position the m3 says 8k and the 325i says 7k. two options.....1. just replace the faceplate on the m3 to a 325i one. note, the 325i econoguage is a larger cutout than the m3 oil temp cutout. 2. get an inline signal modifier. see other post somewhere on this board. there are a couple of vendors that have such a thing. cheers, jason

[aeryk7]

I would recommend 2 bottles of water wetter and half coolant half water combo. It is what is posted for the fan delete kit on bmp , turner etc. or one of those damn performance sites , oh yeah and that is with runnning an 80 deg thermostat.

[b*saint]

Are you using a fan clutch?

[Rev Engineer]

Thanks for the tips. I was thinking I could really use some water-wetter. I think part of the problem with bleeding air is that the radiator appears to be sitting slightly lower than the head. Defiantly lower than the e36. This might be trapping air in the head which has a difficult time making it to the radiator.

I’m not using the fan clutch.

My project to convert the tach signal is moving. I’ve got a micro programmed to drive the tach between 900 and 8000 rpms. Next step is to read the input signal and I should be nearly done. I might be able to make a few extra pc-boards or publish my design. Would anyone here be interested in this?