need help diagnosing overheating issue

[go3go]

Recently did a head gasket job on my e30. Head was pressure tested and the mating surface was machined. Everything was torqued to spec. I have replaced everything in the cooling system with the exception of a few hoses and have installed an electric rad fan. System has been bled properly (heat blows hot even at idle, no air whatsoever from bleed screw).

My problem is that the temp gauge still creeps when the car is sitting. It will be at half, then creep to around 3/4 or slightly above, and occasionally jump around and peg itself in the red. The car exhibits no signs of overheating other than this.

At this point I was considering just replacing the sending unit for the gauge and going through fixes for a bouncing gauge. Now, however, it has stopped bouncing and appears to function normally. When I rev the car up for a few moments (to around 2500 rpms) at idle it will quickly drop back to center, and then begin to creep up again.

So I guess my question is this: are these symptoms still indicative of an issue with the temp sensor/gauge, or should I be looking for something else?

Thanks in advance guys

[dnguyen1963]

Which year is your car? Mine is an '88 325i and when the SI board went south, it exhibited the same symptom.

[Keith M]

Do you still have the stock fan in place? If so the fan clutch may need to be replaced.

[89 e30]

That problem probably comes from your si batteries in your cluster

[go3go]

Do you still have the stock fan in place? If so the fan clutch may need to be replaced.

The stock fan has been replaced with an electric (old fan clutch was toast)

That problem probably comes from your si batteries in your cluster

Which year is your car? Mine is an '88 325i and when the SI board went south, it exhibited the same symptom.

Mine is an 89. Perfect, that's what I was hoping to hear. I'll look into that next. I don't have a lot of experience with e30's (had an e36 for a few years before) so I wasn't 100% if my symptoms were indicative of an actual issue with the cooling system or just the cluster. Thanks!

[codrum]

Have you changed your water pump? Does the electric fan come on at the correct time or is it always on? Have you ever changed your thermostat?

[jlevie]

The stock fan has been replaced with an electric (old fan clutch was toast)

What fan did you use? In my opinion a 16" fan rated for 1800cfm is the minimum. And you can't use the aux fan thermo switch to control the fan. The low temp side of that switch doesn't trigger until the radiator temperature is above 91C when the temperature reaches 99C the low temp switch will open and the high temp switch will close. For proper engine operation that mimics the stock configuration you need an 82-83C thermo switch for the electric fan and a dedicated relay for said fan. If the car retains A/C, the existing thermo switch, relay, and aux fan needs to be retained and operational.

If you have a big enough fan and it is operating at idle, use a contact or IR temperature probe to verify that the engine is running hot. If it is and this isn't a gauge problem, replace the thermostat and if not recently replaced the radiator.

[dnguyen1963]

I would also check the radiator hoses. If you do not have a thermometer probe, you can use your hand temporary. If the upper going into the rad feels hot and the lower coming out of the rad feels cool then it is almost certain that your SI battery/board is bad. If the upper is cool then your t-stat is probable stuck closed. If both hoses are hot then your fan is not cooling enough.

[go3go]

thermostat is brand new and tested, as is the water pump, radiator and most of the radiator hoses. I have used an infrared temp gun on the thermostat housing and it never got above 82-83 degrees

I'm running this 16in spal fan

http://store.bimmerworld.com/spal-electric-fans-p1160.aspx

I am running a relay from bimmerworld as well. Currently it will engage when I hit the ac button. I just hit it anytime I'm sitting at idle or driving below 25-30 for too long. I was looking for a better way to run it so it would engage automatically, but I got really busy when school started again (I didn't realize the stock fan switch was such a high temp). The ac doesn't work, so I'm not worried about just switching out the temp switch.

I've felt the radiator hoses, the top hose gets hot, but the bottom hose stays cool when the fan is on. I haven't let it run without the fan running at idle.

[bernzpeed]

did u bleed the coolant?

[go3go]

Yes, coolant has been bled properly.

[jlevie]

thermostat is brand new and tested, as is the water pump, radiator and most of the radiator hoses. I have used an infrared temp gun on the thermostat housing and it never got above 82-83 degrees

I'm running this 16in spal fan

http://store.bimmerworld.com/spal-electric-fans-p1160.aspx

I am running a relay from bimmerworld as well. Currently it will engage when I hit the ac button. I just hit it anytime I'm sitting at idle or driving below 25-30 for too long. I was looking for a better way to run it so it would engage automatically, but I got really busy when school started again (I didn't realize the stock fan switch was such a high temp). The ac doesn't work, so I'm not worried about just switching out the temp switch.

I've felt the radiator hoses, the top hose gets hot, but the bottom hose stays cool when the fan is on. I haven't let it run without the fan running at idle.

That is a 1300cfm fan, which in my opinion is inadequate. But then your temperature data doesn't support what the gauge is doing.So maybe the engine isn't running hot.

Since this is apparently a street car and since the penalty for a real overheat is, at the least, surfacing of the head and a new head gasket, wire the fan so that it it on when the ignition is on until you can rig it up properly. Or better yet (on a street car) ditch the electric fan and revert to the OE fan and clutch.

[go3go]

That is a 1300cfm fan, which in my opinion is inadequate. But then your temperature data doesn't support what the gauge is doing.So maybe the engine isn't running hot.

Since this is apparently a street car and since the penalty for a real overheat is, at the least, surfacing of the head and a new head gasket, wire the fan so that it it on when the ignition is on until you can rig it up properly. Or better yet (on a street car) ditch the electric fan and revert to the OE fan and clutch.

Ah I was not aware that it was only 1300cfm.
I had the same fan on my e36 for over a year with no issues whatsoever. I'd really like to avoid spending another 80 bucks on a fan clutch if I can. I'm going to order a lower temp fan switch and get it wired up correctly though, in addition to changing out the SI board batteries and see if that fixes the issue.

[Cephas]

Any updates on this? I'm tracking down a similar problem on my 89is.

The temp gauge stays pretty much at halfway until the car sits. When it's sitting, it creeps up slowly, then hits about 3/4 and starts bouncing all over the place. Once the car is moving again, the temp goes down to about 1/2 again.

The PO deleted the auxiliary fan.

I have tested the clutch fan and it's working fine. Upper hose is hot and lower hose is cool. Heater blows hot, so I do not think there's any air in the system.

Do I get a vote for SI board as well?

[dnguyen1963]

Trust me, after some 20 yrs, the leaked acid from the NiCd batteries in your SI board had eaten through many electronic components. Take it out and you'll see what I mean.