Coolant temp tops at 1/4

[flagoworld]

This has been a question on my mind for a while, and I figure I may as well ask it here (finally). My coolant temp never seems to go above 1/4. Before and after the rebuild, the gauge never went above 1/4. I did not replace any of the sensors during the rebuild. That's about 70-80C or something, if I remember correctly? I've been told it was pretty normal, but to me that doesn't seem right. I guess it could be the sensor or gauge acting up, and I can probably check that with a heat gun. Someone must have some actual experience with this though? Whether at full rev or idling, the temp never goes above that 1/4 mark. It's stable, just too low.

Edited May 17, 2018 by flagoworld

[arminyack]

My car is the same way. It only get warmer when it is hot out, and I'm climbing a big hill at full throttle. Even then, it only get to 1/2.

[ingramlee]

Same here...

[flagoworld]

So, if I have a 71C thermostat, I guess this makes perfect sense. I must have one. Why do the thermostats on this car run at such low temps? Most cars are around 200F last I checked, and 71C is 160F. Even the 80C thermostat is only 170F...

[AlfaBMWGuy]

Same here.  Used to go to 1/2 and climb higher in heat/traffic when I first got it last summer, but then I had major work done over winter on the heater core, all hoses, radiator, water pump--everything gone through to bring my '02 back mechanically.  Now it sits at 1/4 and gets to maybe 1/3 in the heat/traffic situations, but so far never higher.  I don't think I have a 71C thermostat either when that was replaced.  I just attribute it to everything being like it should be and I have extra insurance for the 110F+ outside temps coming up this summer.  I have thought about heat gun readings though as a way to make sure it's running hot enough not to result in any longer term issues.

[Schnellvintage]

My car reacts the same as it takes a while to get warm. But is steady and consistent. My infra red temp gauge reads normal temps 175-185F at the top hose and water neck. The lower reads 155-160 and really doesn’t get much higher. I have a High Density radiator , EFI, stubby headers, ported and polished head. I believe the motor is just very efficient.
Matt


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[flagoworld]

1 hour ago, Schnellvintage said:

My car reacts the same as it takes a while to get warm. But is steady and consistent. My infra red temp gauge reads normal temps 175-185F at the top hose and water neck. The lower reads 155-160 and really doesn’t get much higher. I have a High Density radiator , EFI, stubby headers, ported and polished head. I believe the motor is just very efficient.
Matt


Sent from my iPhone using Tapatalk

 

What thermostat do you have installed?

[Schnellvintage]

80 C. Prior T stat was a 71 C. I was dynoed with 128 RWHP and 133 ft lbs.
Matt


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[flagoworld]

OK, I was thinking about replacing mine with an 80C based on what has been said here and some searching around. The temps you stated are closer to an optimal operating temperature by my limited understanding. Also, if I am thinking correctly (...as if...), the lower hose WOULD be cooler, as that is the supply line from the radiator. The upper/neck would be where the water pump is circulating through??

 

Thanks

[TobyB]

Isn't there an 88c t-stat option?

 

The cooler t- stats are a throwback to unpressurized water cooling,

and/or hot spots in the head.  Especially iron heads.

 

Coolant at 15 psi shouldn't boil until 260f (ish) so modern cars 

with well- designed heads run 95c t-stats, 1.5 bar pressures,

and don't have problems.

 

Boiling in a cooling system is death-  short term, it creates high local 

temperatures, super high stresses, and can soften the head casting.  If it doesn't

crack it outright.  Long term, it erodes the metal.

 

All that expounded, yes, an 88c t- stat might be a bit better.  But the M10 isn't 

that sensitive to head temps, so yes, you lose a little efficiency, emissions go up a little,

but the ECU doesn't crap itself and send you to the nearest EPA station for a bare- bottomed spanking.

If the rest of your system is top- notch, sure- crank up the temp.  It's good for everything.

If it's a bit marginal, keep it cool!

 

t

don't get steamed!

[flagoworld]

34 minutes ago, TobyB said:

Isn't there an 88c t-stat option?

 

The cooler t- stats are a throwback to unpressurized water cooling,

and/or hot spots in the head.  Especially iron heads.

 

Coolant at 15 psi shouldn't boil until 260f (ish) so modern cars 

with well- designed heads run 95c t-stats, 1.5 bar pressures,

and don't have problems.

 

Boiling in a cooling system is death-  short term, it creates high local 

temperatures, super high stresses, and can soften the head casting.  If it doesn't

crack it outright.  Long term, it erodes the metal.

 

All that expounded, yes, an 88c t- stat might be a bit better.  But the M10 isn't 

that sensitive to head temps, so yes, you lose a little efficiency, emissions go up a little,

but the ECU doesn't crap itself and send you to the nearest EPA station for a bare- bottomed spanking.

If the rest of your system is top- notch, sure- crank up the temp.  It's good for everything.

If it's a bit marginal, keep it cool!

 

t

don't get steamed!

 

Makes sense. Also, not seeing anything bigger than 80C for 2002. Seeing 88C for later model BMWs though. I think 80C will be just fine, based on what I've been reading and what you guys have been saying.

 

My coolant system should pretty much be functioning top notch. new pump, free and clear radiator, new hoses, very clean coolant passages, etc.

[jimk]

1 hour ago, TobyB said:

Coolant at 15 psi shouldn't boil until 260f (ish) so modern cars 

with well- designed heads run 95c t-stats, 1.5 bar pressures,

and don't have problems.

Last I looked 1.5 bar is more like 21psig.  Ok if your other 40+ year old parts in the system (like the heater core) can stand pressures over what the original design called for.  I tossed the 21psig cap that came with the custom radiator for the s14 and installed a 1.1 bar cap.  No use asking for antifreeze on the feet.

Edited May 21, 2018 by jimk

[TobyB]

Sorry, Jim,

I mixed my automotive metaphors.

 

2002s run at 1 bar (14.7) if you buy the usual cap.

Coolant raises that already- elevated boiling point some more.

 

E30's use 1.4 bar, E36 as well, and by the E46, they're at 2 bar.

Way too much for those poor heater cores, I agree.

 

But any way you cut it, 80c t-stats (if that's what there is)

should have plenty of safety margin before localized boiling starts in.

 

t

[joebarthlow]

This is my experience with my thermostat as well. I'm about to buy a new one as I was thinking it's not working correctly, but now I'm not sure. rides in the bottom 1/4-1/3. on rare occasion reaching about 40%, just under 1/2.

 

I'm concerned because my water pump might be failing. I would assume if that was the case, a properly functioning thermostat would indicate something? I plan to hit mine with a heat gun tomorrow to verify temps. 

 

Can someone explain why there are 71ºC, 75ºC and 80ºC thermostats? The genuine BMW Thermostat Blunt Tech carries doesn't list a temp, anyone know what it may be?

 

thanks

[Stevenc22]

There are different thermostats for different climates. You actually want some heat in the engine but not too much. A higher thermostat is good for cool climates while a lower thermostat is good for hot climates.

 

Mine also runs around 1/3 without AC and maybe 1/2 with AC on a hot Texas day.