1988 325Ic temp sending unit problem

[jjuken]

hi, everyone I'm new to BMW world, I just rebuilt the engine in a 325 I convertible I bought for my wife, It has been a fun and stressful at times project. Like my current issue, I just replaced the original temperature sending unit in the therm housing, I replaced it because the gauge was reading HOT at all times. So I figured the sending unit was bad so I bought the brown unit and the blue one and replaced them both,and it still goes right to HOT, the gauge is good, I checked it by grounding the wire, off and on to watch the gauge go cold to hot, worked fine, what dose anyone think of this ?

[silversled]

sounds you are not sure.... YOU just rebuilt or did you HAVE it rebuilt and you PAID for it...which is it?

[silversled]

So you rebuilt a BMW 2.5 litre engine by your own hand and are confused by a thermostat?.....you don't seem to know what that means...come on here

[silversled]

I think your full of it and don't know even closely what you are speaking of

[jjuken]

YES I REBUILT THE ENGINE, and yes myself. and what the temp gauge is doing I have never seen before, I have read some other helpful treads and they tell me that their are batteries on the gauge pod that need to be replaced. Sorry guys this is my first BMW I have ever worked on, It runs great now but the temp sending unit was clearly giving me false reading. thanks for your interest

[witeshark]

sled, you mind lightening up? Can maybe you (OP) try another sender or maybe have it tested at an auto parts store.

[johnnyBgood]

Originally Posted by jjuken

YES I REBUILT THE ENGINE, and yes myself. and what the temp gauge is doing I have never seen before, I have read some other helpful treads and they tell me that their are batteries on the gauge pod that need to be replaced. Sorry guys this is my first BMW I have ever worked on, It runs great now but the temp sending unit was clearly giving me false reading. thanks for your interest

Hey jjuken, I found this.....maybe it will help you.

erratic temp gauge E30 M3 - BMW CCA

jb

[buggsy487]

I have talked to a few guys and have been told that many 325i's run hot,,,,mine runs between the 1/2 and 3/4 and sometimes near the red. I too have changed the thermostat and heat sensor and am still having problems.

[m20enginebuilder]

Originally Posted by jjuken

YES I REBUILT THE ENGINE, and yes myself. and what the temp gauge is doing I have never seen before, I have read some other helpful treads and they tell me that their are batteries on the gauge pod that need to be replaced. Sorry guys this is my first BMW I have ever worked on, It runs great now but the temp sending unit was clearly giving me false reading. thanks for your interest

Yes there is a battery in the instrument cluster. Im pretty sure, however, it is not for the gages, it is merely for the service interval circuit, it keeps it alive so it keeps the time from when it was last reset to the time to reset when the car is not turned on. The service interval goes off of time, or mileage, one of the 2. And the little chip on the service interval circuit for the service/oil change lights requires a tiny bit of power at ALL times in order for it to function properly and keep the data for the lights to change/come on when theyre sposed to. This battery, also, is a rechargeable lithium unit, and charges when the circuit has power going through it. As far as the temp gage issue, you have an open somewhere in the circuit, or probly more likely in the temp sensor. It COULD very possibly be a faulty one. those kind of things happen from time to time. Me and a friend got some rod bearings recently for his MR2, and we blew one up in 1 mile despite going VERY LIGHTLY on the gas pedal and not giving it much gas. We think the bearings COULD have been defective.

EDIT: ALSO those 2 temp sensor cables LOOK the exact same. BUT one has 2 wires and the other only has ONE wire. If you hook them up to the WRONG sensors, meaning 1 pin connector to 2 pin sensor, and vice versa, neither one of the 2 circuits will function properly. the 2 pin one is for the ECM(if I remember right) for fuel control and open/closed loop operation, the SINGLE pin sensor is for the GAGE. Hook them up backwards, and the ECU will NOT go into closed loop operation and WILL NOT control the fuel properly, and the gage will not function properly either.