Can an engine run TOO cool?

[2nd.amnd]

I just recently got my 86 325e back on the road. Did a lot of work on it including a lot to the cooling system. It has a new water pump, all new coolant hoses and a shiny new radiator.

Changed the coolant and bled the system per the instructions, but now I'm a little concerned about how cool it's running.

Today, on the way home from work, the outside temp was 97f. The temperature gauge never got up to the halfway mark. It was well out of the blue zone, but only a little past the first white mark. I figured it would go up when I was in town in traffic, but the gauge actually went down! The needle was nearly touching the first white mark.

I guess the engine is operating in the correct range but on the low side. And during a heat wave! Is there something wrong or should I be happy my cooling system is working so well?

Thanks!

[ttrousdell]

the thermostat controls the temperature of the coolant. They vary at the temperature at which they open. Did you replace this part?

[strad]

I have completely gone through my cooling system within the first couple years of ownership (owned for seven years now). I know that every component is perfect, and I am running a stock 80 C thermostat. When warmed up, the gauge runs between the mark below half and halfway. New water pump, new thermostat, new radiator, etc. And I also replaced a missing ground nut on the back of the gauge. And it'll run in that range in ambient temps of 112 F here in the desert. So I'd say you're probably ok.

[2nd.amnd]

Nice!

No, I didn't replace the thermostat. Maybe I should buy one to keep on hand. I don't think they are very expensive.

Thanks guys!

[jlevie]

If the cooling system is working properly, ambient temperature is not excessive, A/C isn't in use, and the OE 80C thermostat is installed and working, the needle should stabilize about half way between the 1/4 & 1/2 marks.

[2nd.amnd]

That's just what it's doing, so I guess everything is all right. I just remember it running quite a bit warmer with the old radiator.

OTOH, the old radiator was so rotten you could stick your finger through it in places. About 50 percent of the fins were missing. Stands to reason that the new radiator would be working more efficiently.

Thanks again.

[v8fc3s]

I recently got my car running after stroking it (or changing the top end if you want to get technical) and today I let it run for the longest amount of time since it has been up and in working order again. All in all, I let it idle for a good 10-15 minutes, drove it around the block, and then let it idle for another few minutes. In this whole time the needle didn't move. I'm not sure if it moved a TINY bit or if that was a placebo of me seeing what I wanted to see but the needle stayed pegged on the white line before the blue in the temp. gauge. my temp sensor is plugged in and my cluster is working so I'm not sure I have an issue, I am just worried that for some reason it isnt reading and I don't want it to get into the danger zone. also, I drove it around without a hood so it had very good ventilation, but I don't think enough to keep it THAAT cool. Also, When doing the work I replaced the water pump and thermostat (and I can't remember if I got a cooler running one) but regardless, it should give me a reading of some sort. Any input on this guys?

[russc]

My thermostat was broken wide open, but it would still warm up to the middle mark if I let it idle. It was hitting the quarter mark in traffic and freeway driving. That's at about 70-80 degrees F ambient temp.

I remember reading that a way to test your gauge is to ground it and see if the needle moves.


You can also get an infrared thermometer to take a reading off your engine after letting it idle.

[JinormusJ]

If your cooling system is up to par, it should read around 7/16s (or differently put: a slight tick below the middle mark [1/2] ). This is installed with the OEM 90* thermostat. Your e30 is indeed running cold, unless your needle has been messed with and it is giving you a wrong reading (my e30 suffered from this after a cluster project and was a paint to readjust). I typically opt for the higher/highest degree thermostat whenever it needs changing, just so that I know my heater will be up to par in any condition.

Even then, my temperature fluctuates from 5/16 (one tick above the first white line [1/4] ) to halfway, but stays within the higher range during day driving. My temperature rarely drops in the lower range explained above unless I am driving early in the morning or at night when ambient temps are around 50-60*. During the drive, the temperature only fluctuates in traffic (goes up), or I am coasting in neutral while exiting an off-ramp (goes down)


Engine running too cool is a possible sign of a stuck-open thermostat. You never mentioned anything about the thermostat.

Also, you said new-er waterpump? Is that NEW-New? Or New, but a little used? Did you originally buy it new, or buy it used?

[digger]

when mine had the t-stat stuck open is was blatantly cold never got out of the blue.

my ecu reads off the blue sensor and has been calibrated to give me a digital temp read out rather then rely on the crappy dash gauge which seems excessively sensitive in that middle portion where the 3 ticks are

[nando]

You probably just have a 70 or 75c thermostat. I recommend at least an 80c.