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Car running hot in Arizona! Near 120°C coolant temp
- Thread starter 5hundred
- Start date
No, this is definitely not normal. I would start by investigating whether your electric fans are even running. At the temperature in your picture, both electric fans should be running at high speed. The high-speed fans are primarily a save-the-engine design. Normally the viscous fan and low-speed fans should be enough to control the temperature. I'm in Tucson and unless it is 110 F and I am sitting in a parking lot waiting for someone or in stop-and-go traffic, the high-speed fans rarely activate, and if they do they start to lower the temperature to the point where they are no longer needed. I don't remember when they activate and deactivate. IIRC the high-speed electric fans activate around 102°C 107C. Note: For clarity, the terms low-speed and high-speed fans are referring to the same two electric fans--both run at either low speed or high speed.
If the high-speed fans are not running, then you need to troubleshoot. I can't tell whether you have a face-lifted model ('94-'95) or an earlier model. The face-lifted models have relays for both high and low speed fans with Delco-type fuses on the top. These relays are behind the fuse box. You have to remove the six screws on the fuse box frame to get back to them. The high-speed relay is usually green and low speed is blue. Pull them both out and check the fuses on top.
IIRC, the earlier models use a 30-amp strip fuse located near the driver's side strut tower on the inner fender-well. Remove the fuse and put it in your hand. It could look good but still have a hair-line crack in it so check it out thoroughly.
If the high-speed fans are running, then you need to investigate whether your low-speed fans are running. Those operate from a separate circuit and are activated by the red refrigerant pressure switch on the side of the receiver/dryer. If your refrigerant is low or the switch is bad, this will prevent the low-speed fans from activating. The low-speed fans don't operate all the time, but in Phoenix this time of year with the air conditioning running they should definitely be running. You can bypass this switch with a paperclip for troubleshooting purposes and that would take out low refrigerant or a bad switch from the circuit. Other common causes of the low-speed fans not working are a blown fuse, bad low-speed fan relay, corroded wiring at the step-down resistor located behind the driver's side headlight, or a bad step-down resistor. The fan itself could have failed as we recently saw with a forum member.
Assuming the high-speed and low-speed fans both check out okay, then you should look into other things, like whether the viscous fan clutch is operating properly. Could it be a bad/clogged radiator or thermostat? Coolant ratio too high? What kind of plugs are you running?
If the high-speed fans are not running, then you need to troubleshoot. I can't tell whether you have a face-lifted model ('94-'95) or an earlier model. The face-lifted models have relays for both high and low speed fans with Delco-type fuses on the top. These relays are behind the fuse box. You have to remove the six screws on the fuse box frame to get back to them. The high-speed relay is usually green and low speed is blue. Pull them both out and check the fuses on top.
IIRC, the earlier models use a 30-amp strip fuse located near the driver's side strut tower on the inner fender-well. Remove the fuse and put it in your hand. It could look good but still have a hair-line crack in it so check it out thoroughly.
If the high-speed fans are running, then you need to investigate whether your low-speed fans are running. Those operate from a separate circuit and are activated by the red refrigerant pressure switch on the side of the receiver/dryer. If your refrigerant is low or the switch is bad, this will prevent the low-speed fans from activating. The low-speed fans don't operate all the time, but in Phoenix this time of year with the air conditioning running they should definitely be running. You can bypass this switch with a paperclip for troubleshooting purposes and that would take out low refrigerant or a bad switch from the circuit. Other common causes of the low-speed fans not working are a blown fuse, bad low-speed fan relay, corroded wiring at the step-down resistor located behind the driver's side headlight, or a bad step-down resistor. The fan itself could have failed as we recently saw with a forum member.
Assuming the high-speed and low-speed fans both check out okay, then you should look into other things, like whether the viscous fan clutch is operating properly. Could it be a bad/clogged radiator or thermostat? Coolant ratio too high? What kind of plugs are you running?
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Ditto everything @emerydc8 said above. Some additional comments / questions:
1) The indicated ~118°C coolant temp is NOT NORMAL, even in the indicated 43°C / 110°F ambient temps in Arizona. You should almost never see coolant temp above ~105° on the gauge (about 1 needle width above the unmarked line between 80 and 120). In 110F ambients, I'd expect the normal engine temps to be in the 100-107C range (Jon, does your car stay in this range?).
2) How long have you owned this car? If you've owned it a long time, have temps gradually been increasing? If it's a recent purchase, is there any history of when the thermostat, radiator, fan clutch, etc were last replaced? How many miles since last replacement? Etc etc.
3) You need to perform some detailed troubleshooting to avoid throwing parts at this. If the viscous fan clutch is not engaging AND the electric fans are not running, the temps could be this high even if the cooling system is otherwise ok (good radiator / thermostat / etc).
4) If the electric fans are running on high speed and/or the viscous clutch is engaged, very likely something is wrong with the radiator and/or thermostat. The Behr radiator is NLA but I believe Nissens is available. The OE fan clutch is NLA but can be repaired/adjusted, as suitable aftermarket replacements have become difficult to locate.
5) Jon had a good point about coolant ratio being too high. There's an error in the factory service manual about cooling system capacity, if the last repair shop followed the wrong spec, the car might have 60-70% antifreeze mix which will affect cooling performance slightly (but not to the point of running near 120C). The proper procedure is to drain radiator & engine block, flush with water, and only refill with pre-mixed antifreeze in your desired percentage (50/50 anywhere it can get below freezing, maybe less if the car never leaves Arizona).
1) The indicated ~118°C coolant temp is NOT NORMAL, even in the indicated 43°C / 110°F ambient temps in Arizona. You should almost never see coolant temp above ~105° on the gauge (about 1 needle width above the unmarked line between 80 and 120). In 110F ambients, I'd expect the normal engine temps to be in the 100-107C range (Jon, does your car stay in this range?).
2) How long have you owned this car? If you've owned it a long time, have temps gradually been increasing? If it's a recent purchase, is there any history of when the thermostat, radiator, fan clutch, etc were last replaced? How many miles since last replacement? Etc etc.
3) You need to perform some detailed troubleshooting to avoid throwing parts at this. If the viscous fan clutch is not engaging AND the electric fans are not running, the temps could be this high even if the cooling system is otherwise ok (good radiator / thermostat / etc).
4) If the electric fans are running on high speed and/or the viscous clutch is engaged, very likely something is wrong with the radiator and/or thermostat. The Behr radiator is NLA but I believe Nissens is available. The OE fan clutch is NLA but can be repaired/adjusted, as suitable aftermarket replacements have become difficult to locate.
5) Jon had a good point about coolant ratio being too high. There's an error in the factory service manual about cooling system capacity, if the last repair shop followed the wrong spec, the car might have 60-70% antifreeze mix which will affect cooling performance slightly (but not to the point of running near 120C). The proper procedure is to drain radiator & engine block, flush with water, and only refill with pre-mixed antifreeze in your desired percentage (50/50 anywhere it can get below freezing, maybe less if the car never leaves Arizona).
He is running a 1993 500E, so it would be using the earlier relay/fuse setup.
The strip fuse is VERY DEFINITELY the first place to check. You should REMOVE the fuse (both Phillips screws) and REPLACE it with a new one. Very often these fuses are cracked/broken, but this is not apparent to the eye until the fuse is removed. Numerous members here have thought their fuse was fine with a visual check, but when they remove it, it falls apart, and is the reason for their fans not being operational.
Does the fan run at low speed when you are running your A/C system?
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@5hundred - did you buy this car from MB Market a few months ago?
www.500eboard.co
FOR SALE - 1992 500E, 131kmi, Black/Black, MB Market Auction (Boalsburg, PA) - Canadian spec | Cars for Sale - 500E / E500 ONLY
VIN = WDBEA36E3NB612257 New auction posted at the MB Market: https://thembmarket.com/1992-mercedes-benz-500e-7 Data card (also attached PDF): Mercedes VIN Decoder | Decode Your Mercedes-Benz VIN This 1992 Mercedes-Benz 500E was originally ordered for the Canadian market and was imported...
@5hundred,
Check the fan clutch for sure. My 500E had temperature creep on hot days. It turned out to be the OE FAN CLUTCH which are now NLA. I (and Glen, mostly Glen) replaced it with an ACM fan clutch a few years back. No more problems.
Car runs just above 80 degrees most of the time even when idling for long periods.
Next would be the T-Stat and the radiator. Don’t waste your $$$ changing the coolant until you resolve the problem. Then 50-50 or less G5.
Note that I bought the ACM clutch back in 2017 anticipating replacing it before Covid hit. It’s Chinese but the quality appears to be good so far. Bottom line for the $85.00 I paid for it you could replace it probably 8 times for the price of the OE MB fan clutch plus the PITA labor.
Good Luck
Check the fan clutch for sure. My 500E had temperature creep on hot days. It turned out to be the OE FAN CLUTCH which are now NLA. I (and Glen, mostly Glen) replaced it with an ACM fan clutch a few years back. No more problems.
Car runs just above 80 degrees most of the time even when idling for long periods.Next would be the T-Stat and the radiator. Don’t waste your $$$ changing the coolant until you resolve the problem. Then 50-50 or less G5.
Note that I bought the ACM clutch back in 2017 anticipating replacing it before Covid hit. It’s Chinese but the quality appears to be good so far. Bottom line for the $85.00 I paid for it you could replace it probably 8 times for the price of the OE MB fan clutch plus the PITA labor.
Good Luck
Agree with the previous posts about the fans, radiator, etc.
An inexpensive infrared temp sensor from Harbor Freight might be a good investment to see if the car is actually running that hot. The fan clutches on both my 91 300E and 98 SL500 roar when the coolant temps get high, and after a hot soak the electric fans run at high speed until it cools. One other item to consider would be the water pump. I've seen cavitation due to electrolysis and even the impeller loose on the shaft.
If you need help I'm in the Phoenix area.
An inexpensive infrared temp sensor from Harbor Freight might be a good investment to see if the car is actually running that hot. The fan clutches on both my 91 300E and 98 SL500 roar when the coolant temps get high, and after a hot soak the electric fans run at high speed until it cools. One other item to consider would be the water pump. I've seen cavitation due to electrolysis and even the impeller loose on the shaft.
If you need help I'm in the Phoenix area.
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I have two mods on mine that keep the temperature lower: the resistor soldered between the coolant temperature sensor leads on the intake manifold that tricks the high-speed fans into activating earlier as well as the J. Forgione adjustable screw on the bi-metallic strip, causing the viscous fan to engage at a lower temperature. The viscous fan is so effective that I rarely see temperatures above 100 C. Most of the time it stays at 85 C. It's a bit noisy but I'm willing to tolerate it along with the loss of HP to keep things cool.
If the auxiliary fans turn on and cause the temperature to drop rapidly, this means the cooling system is OK other than airflow... HOWEVER, given this scenario, the viscous fan clutch is very likely to be defective. The temps never should have gotten that high in the first place, if the clutch was engaging properly. The electric fans are meant as a backup airflow mechanism, not the primary airflow.
@5hundred needs to provide more info to help diagnose the issue with his car...
Following onto this thread (rather than making a new one) - could use some opinions.
Yesterday, it was EXTREMELY hot here (ambient temps were creeping up to 109F), my engine temps look to be around 107F (see attached pic) after my drive.
This was after 25 minutes of constant 75MPH+ and then the car sitting still for 5 minutes. Inbetween the drive a good 5-8 minutes of steep hill climb (engine at 4K RPM constant) at 75MPH.
In 2018 I changed the following parts:
TSTAT (MB)
Radiator (MB)
Fan Clutch (FEBI)
Before I go down a rabbit hole of trying to fix any issues, wanted to get people’s thoughts on whether this is worrying…?
Yes the electronic fans were ON and the engine was roaring.
Yesterday, it was EXTREMELY hot here (ambient temps were creeping up to 109F), my engine temps look to be around 107F (see attached pic) after my drive.
This was after 25 minutes of constant 75MPH+ and then the car sitting still for 5 minutes. Inbetween the drive a good 5-8 minutes of steep hill climb (engine at 4K RPM constant) at 75MPH.
In 2018 I changed the following parts:
TSTAT (MB)
Radiator (MB)
Fan Clutch (FEBI)
Before I go down a rabbit hole of trying to fix any issues, wanted to get people’s thoughts on whether this is worrying…?
Yes the electronic fans were ON and the engine was roaring.
Attachments
Matin, the gauges show about 110°C, which is a bit higher than you'd like to see.
However, you said this was after the car was parked for 5 minutes following a 25-min highway cruise and hill climb. What was the engine temp when cruising at 75mph?
However, you said this was after the car was parked for 5 minutes following a 25-min highway cruise and hill climb. What was the engine temp when cruising at 75mph?
It was at the line above the 80C mark.
I always like to focus rather on what the gauge is DOING rather than absolute temp readings. Hill climb and heat soak after being parked will make the gauge climb especially in those ambient temps. As long as the temp comes down and stabilizes under normal driving all is well IMHO. If it stays pegged in the red obviously you have big problems.
isn't there a procedure for recalibrating the oem viscous fan? I haven't been able to find it if so.
The unmarked line is 100C. If it was staying around 100C when driving but increased to ~110C from heat soak afterwards when sitting for 5+ mins, that miiiiight be just on the far side of normal. I'd keep an eye on it though.
Here's a photo I took whilst driving my E500 a couple of days ago. You can see the ambient temp, and the indicated coolant temp. This is at speed, and with the A/C on high.
Normally with sustained freeway driving, and ambient temps above 85F, the coolant temp will creep up to 100-105C indicated, especially if the A/C is on, and I am climbing or the car is otherwise at load. Flat or downhill cruising, keeps the temps at 95-102C indicated. Low-speed operation, such as a parking lot or idling in traffic, keeps the indicated temps at the 90-97C range.
A couple of observations from my photo:
1) You can see the beginnings of DDD on my instrument cluster. I would put it at Stage 1.5 right now. I am not yet ready to address it (I will wait until it gets to Stage 3, which will likely be some years away).
2) Almost ready to turn 150,000 miles. I believe I purchased my car in 2003 with 57,000 miles and change on it. So in ~21 years, I've driven more than 90,000 miles in it.
3) For those wondering, the switches at lower left of the photo (along with red pushbutton above switch, and a black one below it), are the switches for arming the Nitrous-oxide system (red arms, black disarms). The blue toggle switch controls the bottle heater, which heats the nitrous bottle up for optimal gas flow when required.
Normally with sustained freeway driving, and ambient temps above 85F, the coolant temp will creep up to 100-105C indicated, especially if the A/C is on, and I am climbing or the car is otherwise at load. Flat or downhill cruising, keeps the temps at 95-102C indicated. Low-speed operation, such as a parking lot or idling in traffic, keeps the indicated temps at the 90-97C range.
A couple of observations from my photo:
1) You can see the beginnings of DDD on my instrument cluster. I would put it at Stage 1.5 right now. I am not yet ready to address it (I will wait until it gets to Stage 3, which will likely be some years away).
2) Almost ready to turn 150,000 miles. I believe I purchased my car in 2003 with 57,000 miles and change on it. So in ~21 years, I've driven more than 90,000 miles in it.
3) For those wondering, the switches at lower left of the photo (along with red pushbutton above switch, and a black one below it), are the switches for arming the Nitrous-oxide system (red arms, black disarms). The blue toggle switch controls the bottle heater, which heats the nitrous bottle up for optimal gas flow when required.
That's about what I see for my M104 engine. Under extreme conditions in might go slightly above 100 but this is not true.
IR thermometer reveals that real temperature around the thermostat is about 10C lower.
RayH
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