It was very hot here the last couple days, and I noticed after driving on the freeway that while idling the temperature would climb up to the 3/4 mark on the gauge and not go back down (I have been driving this car for 2.5 years and it has never gotten that hot). The aux fan didnt come on at all, so I think that it may not be working. I am a bit concerned because I need to be able to spend 30+ minutes in 5 mph traffic at 110 degrees without it overheating and I'm not sure the cooling system is up to that right now. Is it maybe time for a new radiator?

Two questions:

1) What was the reading on the temperature gauge? "3/4 mark" means nothing to anybody but you.

2) Was the a/c on during this adventure?

A/c doesn't work. And I should have said 2/3, or the next to last mark on the gauge.

The aux fan in that car is only triggered by the AC.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

Hmm, that's what I was afraid of. The aux fan has come on sometimes before but I guess that's for a similar reason as the heater constantly turning on and off by itself than anything else. So with just the belt driven fan the temp should start to drop at idle even when it's 110 out rather than keep going up?

If the a/c doesn't work, the fan will never operate.

We can't help you if you can't read the temperature gauge and report back with an actual temperature of the coolant.

the top mark on the MB cluster should be 120, it's the maximum temp the car is safe to operate at, and it should have red line next to it. I tried to find an image of a gauge to post, and couldn't.

the mark below that should be 100, and it's perfectly safe for the motor to operate there. it's hot where you are, the engine can't unload as much heat, as long as it does not get up to the 120 mark, you should be ok.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

On my 1978 300SD the fan comes on at 200°F and when A/C high side pressure exceeds 240 psi....

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Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership