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OK not sure what I got myself into with the relatively low mileage GL (75k miles). Fixed the EIS yesterday and today on my morning trip on the way home red dash light came on and said pull over showing overheat. Definitely not over heated .. sat for 3-4 minutes and gauged dropped back to normal .. drove 2 miles and it popped right back up… even went into a shutdown type mode. sat a few minutes temp gauge dropped and this time I drove it letting it coast down hills and drove home 5-6 miles no issues … put the icar obd reader… no codes… getting ready for the Star system… any common ideas what sends the temp gauge flying up and back down so quickly ? putting my electronic temp gauge (fluke) touching hoses etc … nothing overheated nothing boiling over etc????
Letting it idle it the driveway with AC on no overheat gauge shows ok??
Last edited by vesiadog; Apr 14, 2024 at 02:08 PM.
Reason: wording
I have had temperature excursions after refilling coolant, presumably due to air pockets, while idling, but revving the motor cleared them out.
There are two basic candidates for a true overheating problem. One is failure of the thermostat, which is a relatively cheap fix. 75K is unusually low mileage for this, and the thermostats are more likely to stick open than closed.
The temperature sender on the thermostat could be at fault if the engine was not actually overheating.
The other possibility is head gasket failure. You probably know the diagnostic steps for that.
Note that the thermostat is electronically controlled, so it is normal to see swings from 180 to 212 during ordinary driving. These swings are not reflected on the dash gauge, which is essentially an idiot light.
I have had temperature excursions after refilling coolant, presumably due to air pockets, while idling, but revving the motor cleared them out.
There are two basic candidates for a true overheating problem. One is failure of the thermostat, which is a relatively cheap fix. 75K is unusually low mileage for this, and the thermostats are more likely to stick open than closed.
The temperature sender on the thermostat could be at fault if the engine was not actually overheating.
The other possibility is head gasket failure. You probably know the diagnostic steps for that.
Note that the thermostat is electronically controlled, so it is normal to see swings from 180 to 212 during ordinary driving. These swings are not reflected on the dash gauge, which is essentially an idiot light.
Eric lots of good questions and as usual I am pulling out what little hair I have left?
I do not think it was running hot at all because when I got home I probed all along the hoses,engine etc with the fluke temp probe… The Star system says the coolant is running hot and like you already stated the idiot gauge on the dash is sitting still as compared to the ride home it was very active.
Do you know where the coolant sensor is located ? Back of one of the heads ? According to the Star system it is asking for more fan motor .. the conversion to Fahrenheit says it is running at 230? I would think this would be boil over conditions and it gets there very fast in the driveway idling ?
You would think that if the true temps were 230F that when I probe the upper radiator hose and manifold/cooler that they would be very high also ?
This Fluke temps are in F
I believe there is a temperature sensor at the thermostat - it has four leads, two for heating the wax element and two (I believe) for a temperature sensor. In case you are not familiar with electrically controlled thermostats, they have a native set point of 212, and the ECU adds heat to the element to make the thermostat open at a lower temperature for certain driving conditions, e.g. full throttle.
There could be another temperature sensor elsewhere. Might see what WIS has to say.
Since you were touching aluminum parts that are in contact with the coolant, I'd say your temperature readings are accurate. Plus, they make sense; given that the ECU thought the temperature was too high, it would do everything it could to open the thermostat all the way, and 180F is about the lower setpoint, with presumably full current applied to the wax motor heating element. I'd guess the temperature sensor is faulty. WIS should tell you what to change in that repair. Do inform if it turns out the sensor is not at the thermostat.
If you change the thermostat, note that the o-ring on the upper radiator hose swells from exposure to the coolant and is often impossible to reuse. Plan to either replace the o-ring (good luck finding the exact size) or replace the upper hose. Mine was not reusable at nine years / 160K miles, reusable at three years / 30K miles..
I believe there is a temperature sensor at the thermostat - it has four leads, two for heating the wax element and two (I believe) for a temperature sensor. In case you are not familiar with electrically controlled thermostats, they have a native set point of 212, and the ECU adds heat to the element to make the thermostat open at a lower temperature for certain driving conditions, e.g. full throttle.
There could be another temperature sensor elsewhere. Might see what WIS has to say.
Since you were touching aluminum parts that are in contact with the coolant, I'd say your temperature readings are accurate. Plus, they make sense; given that the ECU thought the temperature was too high, it would do everything it could to open the thermostat all the way, and 180F is about the lower setpoint, with presumably full current applied to the wax motor heating element. I'd guess the temperature sensor is faulty. WIS should tell you what to change in that repair. Do inform if it turns out the sensor is not at the thermostat.
If you change the thermostat, note that the o-ring on the upper radiator hose swells from exposure to the coolant and is often impossible to reuse. Plan to either replace the o-ring (good luck finding the exact size) or replace the upper hose. Mine was not reusable at nine years / 160K miles, reusable at three years / 30K miles..
After an afternoon of reading and posting I ordered
1. new thermostat and housing ($90)
2.Gasket
3. upper hose ($50)
4. Temp sensor that is near the crank shaft sensor
part number 000-905-61-02 ($22) MB part
5. Snap type ring for the upper hose
I just hope after all this and changing the fluid it is not the Water pump also????
Eric also you are right on about the ecm doing everything to cool the motor including turning up the fan to 100% .
All parts MB except the gasket ..no stock in MB
After an afternoon of reading and posting I ordered
1. new thermostat and housing ($90)
2.Gasket
3. upper hose ($50)
4. Temp sensor that is near the crank shaft sensor
part number 000-905-61-02 ($22) MB part
5. Snap type ring for the upper hose
I just hope after all this and changing the fluid it is not the Water pump also????
Eric also you are right on about the ecm doing everything to cool the motor including turning up the fan to 100% .
All parts MB except the gasket ..no stock in MB
Good to know there is another temperature sensor.
If I were you I would change the sensor on the engine block first to see if that fixes the problem. The thermostats are high reliability parts (150K mile), and your upper hose is probably still good. The water pump is a very high reliability part also. I have reused the snap rings many times. I would not disturb these parts until necessary.
Side note... if there's an air bubble in the system, that can cause a gauge to change very quickly since air heats up so much faster than coolant. If that air bubble ended up at the sensor area, then it would show a rapid increase in temperature... as soon as it moved away, the coolant would cause the temp to swing back down rapidly, as well.
If I were you I would change the sensor on the engine block first to see if that fixes the problem. The thermostats are high reliability parts (150K mile), and your upper hose is probably still good. The water pump is a very high reliability part also. I have reused the snap rings many times. I would not disturb these parts until necessary.
I agree with you on many points. According to FCPEURO the #1 failure is the thermostat. So since I can do that part myself plus I am do to change the antifreeze… I thought might as well change it now.. I agree I feel that the coolant temp sensor is failing .. the biggest problem Is I can’t replace that one myself .. even if I drop the driveshaft (as some claim ) I can’t get to even on my lift… so I will get me son to change it from the top side . The link is for common failures on the 272&273 https://www.fcpeuro.com/blog/the-def...d-m273-engines
I agree with you on many points. According to FCPEURO the #1 failure is the thermostat. So since I can do that part myself plus I am do to change the antifreeze… I thought might as well change it now.. I agree I feel that the coolant temp sensor is failing .. the biggest problem Is I can’t replace that one myself .. even if I drop the driveshaft (as some claim ) I can’t get to even on my lift… so I will get me son to change it from the top side . The link is for common failures on the 272&273 https://www.fcpeuro.com/blog/the-def...d-m273-engines
Is your coolant sensor mounted low on the engine? If so, disregard my comment about an air bubble as that would only apply to a sensor mounted up high.
Is your coolant sensor mounted low on the engine? If so, disregard my comment about an air bubble as that would only apply to a sensor mounted up high.
The picture I found of the coolant temp sensor position. So it is just above the CrankShaft position sensor
Today waiting on parts I decided to drain and flush the cooling system …20 minutes into heating up the flush everything was normal no issues. It is about 70 degrees here just like yesterday afternoon when the problem started so after running the heat I switched over to AC and within 6-7 minutes fan capacity went from 6% to almost 100% and heat shot right up like yesterday. I am almost positive the AC kicked on yesterday when the problem started also. So with AC off an heat back on it is dropping fan and temp down.
I have only owned this car for a few weeks and have not turned the AC ON???
Thoughts? I just called my local INDY who has always serviced our MB AC ISSUES. ??? waiting for return call.
Okay, that's officially crazy. I can see the AC calling for fan, but not the AC causing the temperature reading to rise.
By the way, I wouldn't place too much faith in that list from FCP Euro. There's some head scratchers on there; no one I heard of replaces the thermostat on a preventive basis. The thermostat is an old school wax motor with a little heating coil wrapped around it.
Okay, that's officially crazy. I can see the AC calling for fan, but not the AC causing the temperature reading to rise.
By the way, I wouldn't place too much faith in that list from FCP Euro. There's some head scratchers on there; no one I heard of replaces the thermostat on a preventive basis. The thermostat is an old school wax motor with a little heating coil wrapped around it.
I sat in stupid amazing study the heat management on the Star system????
I have seen overcharged systems cause the fan to run and run. But like you said never seen them cause the heat to climb so quickly ??? My thoughts on the AC is to pull out the charge and weigh in the proper exact amount. I am hoping I wake up tomorrow with some brain storming ?? I have only put on around 500 miles on this car after I changed all fluids , brakes and plugs, filters … the only fluid I was going to do this week was the antifreeze and it will get done in a couple of days after I put in the sensor and thermostat . On the thermostat I have only replaced 1 in 5 MB SUV’s I have owned and it was a M272 with a code thrown for a failed stat… so once again I agree with you ???
I'm stumped. Somehow the ECU is getting bogus high coolant temperature readings because the AC is running.
One clue is that the readings are not weird, like surface of the sun, but high-normal. So it's not total failure of some component. Maybe it's something stupid like the AC high pressure line pressing up against the coolant temperature sensor.
I'm stumped. Somehow the ECU is getting bogus high coolant temperature readings because the AC is running.
One clue is that the readings are not weird, like surface of the sun, but high-normal. So it's not total failure of some component. Maybe it's something stupid like the AC high pressure line pressing up against the coolant temperature sensor.
I will look at the ac lines… I am pretty sure it is a waste of money to put in a new thermostat but I will.. the temp sensor might be acting up but my new area of interest is the H and L pressure readings of the AC compressor… I wish during my flushing of the radiator I would have thrown my gauges on … I will have to wait until the parts get here (temp sensor and thermostat) before refilling with new antifreeze and throwing gauges on…
Today I had a couple of readings during my ac running ?? Low temp at the thermostat housing 160ish and close to 200 at the oil cooler???
I'm stumped. Somehow the ECU is getting bogus high coolant temperature readings because the AC is running.
One clue is that the readings are not weird, like surface of the sun, but high-normal. So it's not total failure of some component. Maybe it's something stupid like the AC high pressure line pressing up against the coolant temperature sensor.
Eric do you remember when you changed your fluid and flushed the system ? How much fluid did you use?
I was reading around 3 gallons?(12.7 quarts for gl550)
I did not measure what I took out but when I refilled for the flush (twice) it only took 1.5 gallons??? Can I have a badly plugged radiator ? thanks Bill
Last edited by vesiadog; Apr 16, 2024 at 01:55 AM.
Reason: wording
Eric do you remember when you changed your fluid and flushed the system ? How much fluid did you use?
I was reading around 3 gallons?(12.7 quarts for gl550)
I did not measure what I took out but when I refilled for the flush (twice) it only took 1.5 gallons??? Can I have a badly plugged radiator ? thanks Bill
I did not pay attention to the fluid volume. I will tell you, however, that I use a 2.5 gallon Blue DEF jug as my temporary storage for when I have to drain the cooling system. From the radiator petcock with the front jacked up I about fill the jug, a little less. So I don't know where the extra gallon would be. Maybe it remains in the heater core and lower passages? Mine is the 4.7 liter motor, so it probably has slightly less capacity.
I would be very suprised if you have a plugged radiator; there is little rustable steel in coolant passages.
I am not familiar with the route the coolant takes, so I can't comment on how this might happen.
However, didn't you previously see similar readings between the two while you were having high system-reported temperature?
Contact thermometers are difficult to use well.
I have used these old Fluke temp probes for years … during engineering heat sink readings and they always lined right up with epoxied thermocouples . My new hobby of installing mini-split heat pump units I always use the old fluke temp probes… I think i have 3 of them.
And yes I had a couple readings where the oil cooler and thermostat housing were almost identical .
Todays findings after a few Dr Appts ( I should be going to see a Shrink for buying another 164 chassis)
Decided to run another 2 gallons of distilled water thru it and hook up my ac gauges… well first it was definitely low on charge and took 18-20oz’s to bring it up to a decent pressure 35# low side and #125 high side while producing 40 degree air on max .
It took over 30 minutes before the fan went on full 100% speed.
I talk to two MB people today .. the parts guy at our local dealership .. he says the most sold part is definitely the thermostat and housing . My Indy shop basically said keep up the good work and let him know what I find because he would be doing the same thing ..
My thoughts after tinkering this afternoon are pretty simple … between my fluke readings and the internal readings there seems to be about a 20 degree difference and I believe that is why the fan is coming on so strong… so going to stick with changing the thermostat and temp sensor .
Last edited by vesiadog; Apr 16, 2024 at 08:32 PM.
Reason: wording
Getting ready to replace a few cooling components and while waiting for thermostat and temp sensor to show up I tore most of it apart.. so far in the top radiator hose and inside the thermostat I am seeing some orange material.. didn’t see it during my 3 flushes with distilled?
Another subject is O-rings
I have a great source for Orings and I sourced the thermostat size at 4mm x 40mm or possible 4mm x 39mm and Viton 75/80 would be a good choice .
I bought the O-rings for the transmission shift spools a couple of years ago for the 2008 GL550 when a couple of orings fell apart and caused a limp mode. Another subject for another day!!
Last edited by vesiadog; Apr 17, 2024 at 05:09 PM.
Reason: wording
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