Coolant Operating Temp?

[Cummmins]

I was just wondering what the correct coolant operating temp should be. My car usually runs a couple of needle widths below the 175* mark. The only time I have ever seen it actually hit 175* was at wide open throttle up a 6% grade for several miles. Not sure if this is normal, or if my t-stat is stuck open.

[JamesDean]

80 C is where all of my cars run unless the a/c is on and its hot/humid outside then it will climb up to 100C and go between those two

[Doktor Bert]

You are about to stir much controversy in your quest for an answer. Coolant temps evoke more heated responses than religious topics.

However, what you describe is how my 617 runs with a 71°C thermostat, which is excellent in my opinion...

[Doktor Bert]

Originally Posted by JamesDean

80 C is where all of my cars run unless the a/c is on and its hot/humid outside then it will climb up to 100C and go between those two

Mine will not go over 175°F-180°F up the 'Grapevine,' WOT (4th gear 75mph) with the A/C on on a 100°F day, but I have a custom radiator made from a high-efficiency Modine core with MBZ brass tanks and 25/75 coolant concentration, along with 9 blade fan and 71°C thermostat.

100°C (212°F) isn't a 'bad' temp for a 617 under load, but I don't like to run them that hot...

[Doktor Bert]

One more thing...

The lower hose is exposed to suction. I always install an anti-collapse spring in ALL lower radiator hoses on EVERYTHING I work on...FWIW

[smiffy6four]

I have an 80c thermostat in my 83 240D auto and that is where the temp stays, unless I climb a mountain with the AC on, then it goes up a few degrees, but not much.

[JamesDean]

Originally Posted by Doktor Bert

Mine will not go over 175°F-180°F up the 'Grapevine,' WOT (4th gear 75mph) with the A/C on on a 100°F day, but I have a custom radiator made from a high-efficiency Modine core with MBZ brass tanks and 25/75 coolant concentration, along with 9 blade fan and 71°C thermostat.

100°C (212°F) isn't a 'bad' temp for a 617 under load, but I don't like to run them that hot...

Ours 617's rarely go over 90C. Its my 602 that will hit 100C with a/c on. I also have the sound encap panels on too so that likely just helps hold in heat as opposed to the nice big engine bay of the 126.

[shertex]

Originally Posted by Doktor Bert

You are about to stir much controversy in your quest for an answer. Coolant temps evoke more heated responses than religious topics.

Nice pun.

[zeke]

My 79 240 D usually runs just above 80*, sometimes, at idle in traffic with AC on in San Antonio during the summer, it will climb to just under 100*

Recently had a water pump fail on the 1980 240D - it had been running hot for a while, and overheated on my wife (got over 120*), so I finally replaced it and the t-stat.

I did not test the t-stat in boiling water (supposed to be an 80* trigger) before installing, but the '80 240D still runs hotter, Just took a road trip to DFW, and it ran at 100* on average. But, the temp would sometimes climb to about 110-115* before the t-stat would open and the temp would drop back down to a bit below 100.

[Cummmins]

Thanks for the help, guys. Are your gauges labeled in metric? Mine is labeled in imperial.

[Doktor Bert]

I've had both USA and Metric. I also run a Stewart-Warner mechanical for verification.

Your cooling system sounds exceptional. I wouldn't touch it...FWIW