Hey all,

Just curious, if I bypass the resistor for the auxiliary fan in front of the radiator, so it comes on high fan with the a/c on (instead of low), will it hurt anything? I'd like to give it a little extra help with cooling during the summer-it seems to get much hotter with the a/c on during the summer when sitting in traffic. Fan clutch is new, and when the a/c is off the temp stays nice and cool. But when its on, temp shoots up in traffic and takes a while to come back down when i speed up again. I figure the high speed fan should keep things nice and cool.

Thanks

1.1K ohm resistor in parallel at the engine temp switch is easier just tricks the fan to come on high speed sooner so A/C system isnt effected.

If you are having cooling troubles it is cooling system related. Turning up the fan won't be solving the real issue.

Especially in NY you should not be having those issues!!

What year is your 300E? M103 or M104?

take a read of this and go through all the steps to try to diagnose what is the weak link
http://w124-zone.com/?p=338

__________________
2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

or do a search and try to find a cool harness which will turn on your high speed fan at a liwer temp rather than the usual 105....i think it turns on your high speed fans at 92 degrees

__________________

1990 190E 3.0L

Cool Harness is just a resistor wired in parallel with the coolant temp sensor, as macdrone said above, nothing more than that. Are you experiencing this now with cooler weather, or just during the summer heat? As ps2cho said, this doesn't seem like an airflow problem, particularly at this time of year. It's more likely a coolant problem (or bad temp gauge). Has the coolant system been serviced recently? Right coolant mix, correct/working thermostat, no debris between rad and condenser, no pressure leaks, tight reservoir cap, etc.

__________________
1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't

cal, now that you pointed it out, I remember I actually had the same problem. it was the coolant temp switch. I replaced it a few months ago and did a flush and added new coolant (xerex) and the problem has been fixed. might wanna try that out stormy, pretty sure the 300E doesn't vary much from my 190

__________________

1990 190E 3.0L

Thanks for the replies everyone. It's an 87 with the m103. A little more detail about the problem: it runs hot ONLY with the a/c on and stuck in traffic (idling). The coolant reservoir, cap and level sensor are brand new. Sensors in cylinder head are original (how do I unscrew the green three pole one, there's no room for a wrench or crow foot?). Fan clutch is new and works perfect. water pump has about 70K on it. How do I know if I have the right thermostat? it normally runs just slightly above the 80 degree celsius mark. Currently running Prestone 50/50 prediluted mix (I know, I know!!) Coolant flush and refill with the mercedes stuff coming soon... Did I mention it has 212,000 miles on it?

Oh, and since I'm not using the a/c this time of year, it's not getting hot. and the radiator and condensor (which is new) are clean.

hello,

i dont get what do you consider hot or too hot? how high is the temp gauge getting? i'm pretty sure that the marks on the temperature gauge are in 20 degree increments , and i'm pretty sure that the normal operating temperature for the m103 is 87-90 degrees celsius.

so... if the temperature needle is between the 80 C and 100 C marks, that seems like its normal operating temperature.

ps an engine runing at less than normal operating temperature 90 C is not good, for a number of reasons.

tim

timmyr,

gauge stays in between 80 and the next mark (100?) with the a/c OFF like its supposed to. with the a/c ON, it will shoot up past that when I'm at idle in traffic. If i let it, it would go all the way up. Again, it does this ONLY when the air conditioning is ON.

The increase load is pulling power away from your water pump's ability to push coolant around the system.
I think it is barely keeping the system cool with the A/C off, but with it engaged, it tips it over the edge and cannot provide enough circulation to keep the engine cool.

It is the only logical reason I can think of. 70k is a short lifespan, but its possible.
The coolant type isnt the issue although you should be running Zerex G-05, but regardless thats not the issue. You could be running straight tap water and be cooling OK.

Just because the cap is is new, does not mean pressure is holding. It could be leaking out of tons of places. You need to find out if it is holding pressure. No pressure, no cooling. You also need to make sure the level is OK. Triple check it. Top up until it overflows and wait. If it does not go down after 5 minutes you know 100% sure the system is filled. Just remove the excess with a turkey baster and rule it off the list.

A/C off should hold @ the thermostat mark. 79C or 87C. Most likely 87C. Any higher is indication of some sort of issue.

__________________
2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

The aux fans are triggered to run at low speed via the temp and pressure switches on the AC drier. When the temp rises too high the switch on the head triggers the fans to run at high speed (loud).

When AC is off, the aux fans turn off when refrigerant temp and pressure lowers.

Check the drier switches first, then the switch/sensor at the head.

Replaced the head switch on my m103 (190E) because the fans always ran high speed (switch might have probably shorted out). Now the aux fans work on low with the AC on, then switch to high when engine temp rises.

__________________
http://farm8.staticflickr.com/7271/7...144c3fc1dc.jpg

stormy, suggest installing a new Wahler thermostat. It's likely the existing one doesn't open completely, causing the engine temperature to rise. I have had the same symptoms, only in the Winter months. Replacing the thermostat resolved the problem. Be sure to orient the new thermostat with the ball toward the fire wall.

Fill the engine block with coolant (you should see coolant just below the thermostat) and fill the radiator with coolant using a clear piece of tubing attached to the upper radiator hose connection. After reassembly get the engine to operating temperature and check the coolant level in the expansion tank. If the coolant level is low wait for the engine to cool and add coolant to the full line. Use a 50/50 mix of either genuine MB coolant, or Zerex G-05, and water.

A defective thermostat restricts coolant flow. Unless you see evidence of a leaking water pump seal (coolant coming out the weep hole, or white residue from the weep hole) there should be no need to replace the water pump.

__________________
Fred Hoelzle

Hello everyone,

1. Sorry to revive this old thread of mine, but I figured I'd just add a bit of closure to my original issue, as I finally have time to really work on the car again after a few years of working crazy hours!

I wound up replacing the radiator due to a crack in one of the tanks, and now it runs as cool as a cucumber at all times, regardless of a/c on or not. I used a behr radiator.

however, a side issue has arisen where the electric auxiliary fan runs constantly, and I have determined that the 3-pole green switch is the problem.
My question is: how do you unscrew it?? I cant see where there is enough room to get any kind of tool on it to unscrew it!

hope everyone is well
-Chris

__________________
Streetside: 1987 Mercedes 300E Petrol Blue/Green
2014 Ford Mustang Grabber Blue
1999 Ford Ranger Green

Dockside: 1968 Eltro 17
1985 Silverton 34C

Picture please.

__________________

1990 190E 3.0L