I certain, buried in these posts somewhere, is discussion as to a thermostat solution for the ever-popular problems we (and especially those with E500s) tend to have with cars running hot in traffic, losing power, etc etc. However, I couldn't find it, so I'll hopefully hear from a few of you.

To those 'in the know': is there available an aftermarket thermostat with a lower yield for activating the auxiliary cooling fans and clutch-driven fan? I'm under the impression that these devices are all switched on by the thermo, which doesn't even kick mine on until I'm halfway between 100 degrees and "uh-oh". They work very well once on - why not get them to spin at a lower temp before things get really heated?

Ihave owned Benz's for 40 years and everyone was border-line hot running under the right conditions. I have wired many with a cabin switch with great results. Get stuck somewhere in traffic or such, and put it on . A NICE feature.
On yours , this is simply done by bridging the high pressure switch with the cabin switch at the a/c drier.This is the slow speed aux. fan circuit.
You can get into the high speed fan also with a little circuitry.

I don't think the termostat has any afect on setings of the fans (main and aux). There probably is a way of modifying this setings. I assume that aux fans have a tempreture sencor somewhere. Also there is a summer termostat that does open at lower tempreture. I just replaced mine due to the same problem that you described. According to the mechanic it was a "summer termostat" but i don't belive him. In any case, two days later I got stuck in trafick and the temp went up again (110C). Now I am seriously considering the switch in cabin to turn on the aux fans, looks to me like the only solution to it. May be Arthur can give us some detail how to do this safely.

Here are the setings for the fans on W124:
Viscousus fan clutch on at 96-104 C
Aux fan on at 107, off at 100.

Dmitry

90' 300CE

The thermostat is just a "valve" that redirects and/or blocks coolant flow -- it is NOT linked to any accessories.
I think these things (aux. fan, etc.) that you asked about are controlled by some electrical sensors -- they open or close a circuit (sometimes "grounding" a circuit) at some preset temperature, in turn activating a relay that energizes the fan, etc. You might look into substituting a different sensor that is preset to a lower temperature.

hi what would happen besides taking longer to warm by remove the thermostat completly, would this effect anything else, is i am going to move to Az in Aug. for a year and was just thinking about the heat? Well thank Aaron

Dear wby300:

Never attempt to remove the thermostat completely. MB cooling system uses a bypass cooling design, in which the thermostat will completely open when the actual temperature has reached its intended specification (usually 87 or higher). At the open position, the thermostat will completely shut down the bypass hole, forcing the circulating coolant from engine block to flow into the UPPER radiator hose, and to the radiator itself for heat dissipation.

Therefore, removing a thermostat will likely render your car more vulnerable to overheat condition, because coolant will keep circulating within the engine block in a vicious cycle, without being able to move to the radiator for heat dissipation.

Eric

Some people DO NOT realize, the thermostat is also a controlled coolant flow restrictor.
By only letting coolant circulate at a certain flowrate, the coolant stays in the radiator ( where it cools off ), for a specific amount of time.
Over the years I have seen vehicles overheat ( in warmer temperature weather ), because the thermostat was removed!

__________________
2007 C 230 Sport.

There was a post on the SL forum that addressed this problem in the 107's which have a two-stage thermostat. It recommended drilling three holes in the perimeter of the 'stat and helped keep the temperature under 100.

380SL Temp Guage Reading?

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

k6jrf has a solution to the late aux fan turn on that involves adding a 1%, 1/4 watt 1.1K ohm film resistor in parallel with the coolant sensor. This results in a high speed aux fan turn on temp. of approx. 92 deg. C. His web page is here.

Chuck, I don't know if the thermostat types of the 380 and 500E are identical. If they are not, the modification you have referenced will not work but instead applies to most 380/500 V8's used in the 126/107 bodies. According to my shop manual, MB used three different thermostats in the 116/117 alloy engines--the first was located and operated like the 4.5 V8, the second is located on top of the water pump and has the arm to close off a small bypass orifice that supposedly helps with emissions by warming the head/valve area when cold, and the final version (420/560) back to a more conventional thermostat located on the side of the water pump. The middle version is the problematic version for a variety of reasons not the least of which is its 84 deg C opening point (I recall that the original 4.5 thermostat opened at 75 deg C and the 420/560 open at 80 deg C). I have not been able to locate a thermostat for the middle version with a lower opening temperature although the physical size of many other MB thermostats are identical since the middle version thermostat has the wax pellet mounted on top of the thermostat and the others have it mounted on the bottom of the thermostat (I tried one once on my 380 SE and the thermostat wouldn't open until the water temp got way too hot). Also, it is not possible to invert the thermostat because then the bypass would never close. I have often wondered if changing the water pump, pulley, thermostat and hoses to the last version was possible or if the timing cover also had to be replaced. Anybody done this? Mark.

There is wide misunderstanding of thermostat function. It's primary function is to set the LOWEST operating temperature boundary. Thus, installing a lower temperature thermostat will NOT reduce maximum coolant temperature in hot weather stop and go driving. The thermostat also acts as a restrictor to establish maximum coolant flow rate, so removing it is a BAAAAAAD idea!

The MAXIMUM operating temperature is a function of radiator cooling capacity and air flow through the radiator, and this is where the fans come in.

It would be difficult to alter the engagement characteristics of the mechanically driven fan clutch, so the cut-in point of the electric fan(s) is all that's left, and the simplest mod would be to install a manual "ON" switch in the circuit, controllable by the driver.

Most OEs set the fan engagement point near 230F/110C, which they find acceptable, but, like most, I consider this too high. If it were my design choice, I would set up the control system to engage the fan(s) at low speed when the coolant temp is over 205F/97C anytime vehicle speed drops below 15 MPH.

If the A/C is on, the coolant temperature will often be lower than with the A/C off because the A/C pressure switch will turn on the elecric fan(s) periodically to provide cooling air for the condenser to meet A/C cooling demand.

Duke

Duke, you are right about not wanting to remove the thermostat all together-very bad idea. However, on the typical MB thermostat installation running a lower temperature thermostat can reduce the normal operating temperature on a warm day since the lower temperature thermostat will close the bypass that much earlier to send more or all of the coolant through the radiator instead of recirculating uncooled coolant back through the engine. For example, on the 75, 84 and 80 deg C thermostat examples I gave above, the fully open temperatures given by the MB shop manual (thus the fully closed bypass temps) are 92, 99 and 94 deg C respectively. In fact, I have installed the 75 deg 4.5 V8 thermostat in my 91 300TE (with the vent valve reinstalled on the correct side for this vehicle) and the car runs significantly cooler on hot days--82 to 85 deg C with fast driving on the highway with A/C. Around town driving produces the same results as long as the aux fans come on at the appropriate times. Just so happens this thermostat is the correct physical size and has the correct sized bypass cutoff for this car. As I said earlier, I have not been able to locate a suitable replacement for the one armed bandit thermostat used on the 126 380/500 engines.

A lower temperature thermostat my extend the time it takes to reach a steady state temperature while idling or in low speed traffic because it will sent full flow to the radiator sooner, but the steady state temperature in traffic is ultimately determined by air flow through the radiator.

Say at 90F ambient it will take longer to get to 105C if you start out at 80C rather than 90C, but in extended bumper to bumper traffic both will eventually achieve the same temperature range, which is controlled by the fan algorithm.

Of course, in steady speed driving, especially in cooler weather a lower temperarture thermostat will reduce operating temperature because there is enough radiator heat transfer capacity to keep the temperature just above themostat opening temperature.

Aluminum engines like to run hot - either aluminum head(s) or all aluminum engines. Since aluminum only has about one third the thermal resistance of iron, they more readily transfer heat to the cooling jacket - heat that could otherwise be turned into useful work at the crankshaft. The hotter an aluminum engine (within reasonable limits), the better its thermal efficiency. Also, higher coolant temps tend to reduce engine out emissions and reduce blowby condensation in the crankcase.

I recall about 20 years ago I was running my Cosworth Vega with the Porsche Owners' Club at Riverside. It was about 105 ambient, and the CV was running hot because the radiator was getting clogged up with silicates and other salts from the traditional green antifreeze. The coolant temperature stabilized at about 230F, and gave me some concern, but it had never run better. Not long after I removed the radiator for a "rod out" and operating temperature dropped back to the normal 195F.

Duke

I have read that this cooolant additive lowers temperatures by 5 to 7 degrees. If this is true, wouldn't it help?

__________________
87 300e (white/black; amg body kit)
88 300ce (red/cream; amg body kit)
93 300ce cabrio (white/blue/blue top)
93 300ce cabrio (black/grey/black top)
98 ml 320 (totaled @ 137,000 miles)
99 clk320 (black/grey/black top)

There are people here who swear by Wetter Water. I've tried it and saw no reduction in temp.

What did help with summer-time temps was a reduced ratio of coolant/water..ie...less coolant/more water.

If you live in Michigan, this might cause problems come winter time. If you live in Phoenix, it won't.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"