93 bmw underheating, is this bad?

duke250, Mar 21, 7:44am
I have a 93 318i. I think the termostat is going bad as it takes forever to reach normal temp and sometimes it gets stuck 1/2 way to operating temp,when it does heater only blows warm air. I will get this fix but in the meantime, can the engine suffer any permanent problems if it is run warm and not at operating temp!

msigg, Mar 21, 7:50am
No won't do any damage, may use slightly more fuel not running at correct operating temp, get it fixed before the weather cools down too much, then you will be able to have a have a heater again.

sr2, Mar 21, 7:57am
OK for a short while but I'd be a little hesitant to drive it like that for any length of time.
Engines are made with a number of different metals and alloys, many of which have significantly different coefficient's of expansion.
Internal tolerance's are set to operate within a specific heat range; there could be the risk of increased wear if you drive with it outside this heat range.
I'd play it save and get it fixed soon.

franc123, Mar 21, 7:59am
needs to be sorted ASAP, excessive fuel consumption and increased bore/ring wear are just two side effects of an engine thats running too cold.

saxman99, Mar 21, 8:02pm
Also check the temperature sensor, it might be telling lies to the gauge.I had the same problem in my 1993 318i and the thermo was fine, it was indeed a crook coolant temp sensor.

Which engine is in yours!

lugee, Mar 21, 8:34pm
OP said heater is only warm, rules out sender unit.

gmphil, Mar 21, 8:37pm
Will most likely be that!as cars dont underheat, if ur thermostat crook ie stuck closed will over heat other way round stuck open wont under heat as it will reach running temp

duke250, Mar 21, 10:04pm
Good ol M40, im pretty sure its the thermostate as it eventually reaches operating temp if driven for 30 mins, but as soon as I turn the heater on it blows hot like it should but the temp guage starts falling.

saxman99, Mar 21, 10:35pm
Yep, more likely thermo then, jammed open I guess.Mine was M40 also, great little engine did 370,000 k and never missed a beat even though I did my best to beat the snot out of it.

duke250, Mar 21, 11:17pm
I know right! I had a small 2 door e30 with an m40 and the engine was soo strong and could not be killed tho it did sound like a sewing machine. Even when a truck slammed into it, was still rubning! I think the only things that can kill it is a snapped cambelt or overheating it, its iron cast.