Thank You.

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A Dalton

Ok. I have tried test #2 with success...both fans came on low!!!
After checking that water level was OK, let idle for about 15 minutes and temp only reached about 90C. So, I took about 20 mile test drive. I had A/C on high until about 8 miles out at 50mph; at that point temp started rising and when it reached 110 I turn on heat/defrost for about 2 minutes and temp came back down to 85-90C. Once I got back into town driving 20-30mph and having to stop twice temp was back up to 100C until I pulled into driveway. Once idling it came back down to 90C and stayed there for another 15 minutes or so. (Note: changed the thermostat from a 194F to 180F).

OK

Low fan circuit is now verified as working,,,but now you want to know if the low fans come on when a/c comes on.
So, when car is up to temp and a./c is On, do the low fans come ON? If yes..that is not the problem..if No, then you have a low frigerant level and the fans are not being triggered b/c the high side is not getting to the spec pressure to put the fans ON

What I really now need is to drive the car w/o ac at all and watch the temp gauge..if it gets to 110, do the HIGH fANS come ON?

What I want you to be aware of is the facts that that HIGH fans are triggered by the coolant temps only..via the blu sensor.
The LOW fans are triggered by the a/c high side pressure ONLY...they are a completely different circuit and function.

So , if we do not use the a/c for a test run and the car still o-heats , we want to know if the blu sensor is bringing on the HIGH fans above 105C
That is the test.
I also want you to make sure the fans are turning the direction of the arrows on the fan hub..........

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A Dalton

-Yes, when the car is up to temp and the a/c is turned on the low fans do come on.

"What I really now need is to drive the car w/o ac at all and watch the temp gauge..if it gets to 110, do the HIGH fANS come ON?
-I drove the car for about an hour (roughly 50 miles) during the heat of the day w/the a/c turned off and could only get the temp up to about 95C (w/the 180F/82C t-stat in it). During the last leg of the trip I had to cool off a little, about 2 minutes after turning the a/c on the temp rose to just above 100. I turned the a/c off again and the temp dropped back down to around 90 and stayed there.

"I also want you to make sure the fans are turning the direction of the arrows on the fan hub.........."
-Yes, the are turning in the direction of the arrows (clockwise).

>

Next time do not turn the ac off so you can see if the high fans come On at 105..that is the question.

My advice to you is to change the AF/H20 mixture to 40/60...you have it backwards . H20 carries the heat away..AF does not.
And then I would clean out the condenser as best as you can..a power washer works well..they get full of crap you do not see and the airflow gets restricted... and look between the radiator and condenser too..lots of stuff gets in there........it shows up when the a/c gets turned on b/c the condenser gets hot and it can't disapate the heat away if the fins are full of crap........so the radiator gets burdened with passive heat from condenser, so the engine coolant rises...........

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A Dalton

Just beware. I had to pull off the aux fans because they were both nonfunctional. There was a ton of crud that got pushed into the air vents for the electric motor including bugs, leaves, and stone chips. Once I held these up, picked at and blew these out, they worked fine. As noted by others, a bunch of crud gets caught between the fan brakets and the AC coils. Wacking at the motors may only move the dirt around only to interrupt the fan function at a later date. Something to watch for.

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Brian G.

1994 E320 Wagon with many warts SOLD
1995 E320 Wagon with a beauty mark or two FOR SALE

The best/correct way to clean the condenser out is from the back side ..The dirt comes into the fins from the front , so if you clean it from the front, you have to push the crap all the way tru the fins and cross pipes and it then winds up in the radiator core..
Anytime one does a radiator removal, that is the time to clean the cond with pressure from the back side while the rad is out. I do them weather they look like they need it or not b/c that is the opportune time.
And if you have a bad cond [ I mean bad], it is best to pull the rad and do it right... you would be surprised how well your a/c works with a clean condenser......along with the engine getting better airflow. You should be able to see a light thru-out the entire cond ...and if you do us a power wash ..do not come in from the sides b/c you can bend over the fins ..straight ahead is the trick.

Same goes for your Condenser unit outside if you have Central Air @ Home............they have to breathe........

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A Dalton

Hey AD,
I'm back this is my b/f's car I only get to drive it and work on it when something is wrong. We're both mechanically inclined, but I'm the mechanic (because I have the patience of a mother to work on it...and go figure...I work in a fleet maintenance shop).

I did pressure wash the condenser from the backside when I replaced the radiator a month ago because there was alot of crud that fell out when I pulled the old radiator out..

Since it boiled over just before putting in the 180 thermostat, we refilled it, burped it, and refilled it again with H2O. I believe the AF/H2O should be about 40/60 now.

B/F just called me from in Memphis and said that it started overheating again. Temp gauge got up to 120, and remembering what I had told him, checked to see of the HIGH fans can on and they did. So, the blue sensor is good...Now what?

Could be:
Thermostat
Viscous Fan
Air pocket

Did you put the fan shroud back on when the radiator was put back??

..may even be more serious..lke a head gasket.

Do a search on Viscous Fan test.. and have him run it w/cap off and burp it for air pocket, on an incline, if possible.

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A Dalton

Yes, I did put the fan shroud (the wonderful 2-piece thing that it is) back on when I put the new radiator in. Unlike some folks I don't usually have spare parts after doing mechanic work just old parts I've replaced.
It seems strange that after I've replaced or checked something that it runs fine with no problems for a week or so then decides to overheat again. I check, before & after I've driven it, for several days to make sure the fluid level is good in case it has burbed while driving, refilling it to proper level when necessary.
We've gone through 3 thermostats, and checked regularly for cleared air pockets, my only guess is that it's either the Viscous Fan or, as bad as I hate to say it, a bad head gasket.
I'll do a search on the Viscous Fan test and get him to burp it some more. Hopefully he can get it home tonight so we can check it out again tomorrow.
Thanks again.

Well, seeing you work on cars , I might recommend that you take those two connectors I had you jumper at the reciever/drier and hook a wire to each and fish it thu to the cabin with a toggle sw.
Then when you see the heat climbing, you can flip the sw and see if added airflow solves the problem..it it does not , then water flow is suspect..if it does , then airflow is suspect.
Many guys put a manual over-ride sw like this in that exact part of the circuit for towing and emergency heat conditions just for saftey sakes ..it can come in handy in traffic , etc. and gives the driver some control of temp in high thermal conditions.
You still have not verified that the HIGH FAN comes On at 105..if the sensors is out of wack, it will still work, but it may be coming on late [ like 115C]..see why I keep asking that question? [I now realize that you are not the one driving this car , so the second handed info may add to the confusion.] There is a Temp/Ohms chart that has those specs to confirm the cut-in of that sensor for just that reason.
Many guys also bridge that sensor [ the blu one] with a resistor of proper value to bring the cut-in of the high fan down to around 100C , vs the factory 105C..that is a simple , .99 cent modification that works well on that system.
I am inclined to think you have a sticking thermo just b/c of the intermittant character of the complaint. [ or air pocket] Are you using cheapo thermos ??
..or a bad viscous , showing up on high temp days/loads......
A head gasket would most likely fail consistantly..

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A Dalton

I'll try the over-ride switch idea and see if that helps. I have done this a few times before on Ford solenoids when neutral safety switch was bad but with a pushbutton switch.

I got to drive the car in to work this morning (about 9mls@55mph & 4mls@35-45mph). During my 12 minute drive here's what happened:
The first 3mls temp gauge stayed @ 40
next 5mls temp gauge read 80
next 2mls @ 85
next 1ml @ 90
next 1ml @ 100
during the last mile temp shot up to 118 and stayed there. Turned defroster on to try to cycle some of the heat and only blew cold from all vents. Also tried other buttons and temp controller...all air blew cool/cold from all vents. He had this same problem.

"You still have not verified that the HIGH FAN comes On at 105..if the sensors is out of wack, it will still work, but it may be coming on late [ like 115C]..see why I keep asking that question?"
The HIGH fan came on around 110-115 (radio off/windows down...I could hear it).

"Many guys also bridge that sensor [the blu one] with a resistor of proper value to bring the cut-in of the high fan down to around 100C , vs the factory 105C..that is a simple , .99 cent modification that works well on that system."
What is the proper value of resistor needed to do this? I'm willing to try just about anything at this point.

"I am inclined to think you have a sticking thermo just b/c of the intermittant character of the complaint. [ or air pocket] Are you using cheapo thermos ??"
We have tried two different 194 degree thermos and current one in is 180 degree all three were from NAPA, all are Stant brand. I've never had this problem before with their thermos. One thing I did notice when I replaced the original thermo...there was no o-ring gasket and the housing was sealed with Red RTV. I am using the o-ring gasket with the thermos I have been installing but the thermos all have a seep hole in them (so, I don't feel this has much to do with out problem).

Viscous fan seems to be okay (from the others posts I've read here)...fan spins freely, at least 3 revs, when it is cool. When its hot/overheated I can't even get a quarter rev, it has alot of resistance.

High fan is coming on late .On the thermo, we always use ONLY Rehr b/c of problems with others..the thermo has to be suspended in the rubber ring as a mount ..it also has to be with the vent properly located for venting..
Try the manual low fan sw and that shoud give you some insight..

I will post the resistor values or go to JimF site ..he sells a manufactured one that just plugs in...

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A Dalton

I've been lurking this thread, mostly because I too have a 300E 2.8. At what point in your drive did the temperature begin to rise? On the highway, or only after exiting? A bit of a spike is normal when exiting the highway, though not that much.

The temp guage sitting on 40c for so long seems odd. My cars are at 60c before I make the half mile out of the neighborhood, and at 80c well before 2 miles. How confident are you that the temp guage is accurate? The dash guage and the high speed fan use two different sensors, so they fail independently.

The car does have an adequate cooling system, so it can be made to behave. I live in Dallas and never see more than 85c or maybe 90c on the hottest of days. Last weekend was 108F and the car stayed at 90c in stop and go traffic, with the electric fans running constantly at low speed. The only time I've ever seen the engine reach 105c and trigger high speed fan was when the low speed fan resistor burned out.

I'd likely try a citric acid flush of the cooling system and Behr themostat next, but gut feel is the water pump. Seems it moves enough (barely) coolant to dump the heat at sustained highway speeds, but the lower engine RPM around town causes the car to heat up - perhaps because of inadequate coolant flow?

- JimY

Hi JimY,
We are in Memphis and our temps outside aren't quite as hot as yours but close enough. This car ran great for two years b/f has had it; within the last year developed small crack in rad that JBWeld held tight until about 2 months ago when I replaced rad. We have only had this problem since replacing radiator. I've contacted Wiley Imports (an exclusive MB parts/service/salvage shop) here in Memphis. He has the Behr thermo and correct rad/tank cap for about $35 for both. I'm going by to get them Monday. It's holds @ about 82-85C on the highway and spikes to about 95 when exiting, but at slower speeds, 40mph and under, is when it really starts heating up/overheating. I'm not giving up on this problem. I'll keep trying til I get it right.
Thanks for lurking.
DebN