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Hi all. Im not sure if Im going crazy but I got my car back from repair and it seemed like the coolant was heating up extremely quickly. Ambient temp was 77 this morning. Within a tenth of a mile the temps were 141(oil 82) . car was started and driven, not warmed up at idle. At one mile, 183 (oil 102) Within 1.5 miles I was at 197(oil 127). Temps remained there. Oil got to 174 by the time I got to the dealership (the whole trip was 1.5 miles) and coolant was 197.
I dropped it back at the dealership since maybe there is a bubble in the cooling system..
What are your thoughts. Its been hot as **** but these number were at 77 degrees, rpms kept below 2000, ac off.
Thanks!
Last edited by Baltistyle; Jul 2, 2025 at 11:50 AM.
Hi all. Im not sure if Im going crazy but I got my car back from repair and it seemed like the coolant was heating up extremely quickly. Ambient temp was 77 this morning. Within a tenth of a mile the temps were 141(oil 82) . car was started and driven, not warmed up at idle. At one mile, 183 (oil 102) Within 1.5 miles I was at 197(oil 127). Temps remained there. Oil got to 174 by the time I got to the dealership (the whole trip was 1.5 miles) and coolant was 197.
I dropped it back at the dealership since maybe there is a bubble in the cooling system..
What are your thoughts. Its been hot as **** but these number were at 77 degrees, rpms kept below 2000, ac off.
Thanks!
Your coolant is warming up quickly. This shows tstat is doing its job from closed to opened temp.
Why is your oil is not picking heat?
It's getting slowly warmed up by the coolant...
Have you noticed your pistons accumulating heat??
> Simple test...:
Under same cold engine conditions, drive by downshifting to keep running near 2500.Rpm.
This will effectively remove your pistons heat with oil.
Last edited by CaliBenzDriver; Jul 2, 2025 at 02:11 PM.
I haven’t updated my thread for the Fidelity warranty, but I just had the rear heater coupling replaced, and the wiring harness for the oil control solenoid inside the pan. They also re-gasketed the oil cooler and the oil thermostat cover in the cooler. Intake off for the coupler, then valve cleaning.
So they’ve had a lot of the car apart… I didn’t do much digging or driving because it seemed odd and I just wanted to get it back to them.
I don’t have the car right now to try driving it differently, but in this test, I basically didn’t hit the gas very much because I was strictly monitoring how quickly the coolant was getting hot. The oil still seemed to get hot in about eight minutes.. they were just drastically different.
no codes. Fan is working. Intercooler pump seemed to be working. The thermostat did not open up at 197° though…. so I was unable to check flow through the radiator or drive it enough to maybe force any air out of the radiator.
so, Cali, you look at this as slow oil heating versus extremely fast coolant heating? Solenoid is plugged in right now due to warranty work, but historically temps were always much closer regardless of solenoid.. i’ve just never seen coolant get to this temperature by the time I pulled out of my neighborhood.
Last edited by Baltistyle; Jul 2, 2025 at 02:11 PM.
I haven’t updated my thread for the Fidelity warranty, but I just had the rear heater coupling replaced, and the wiring harness for the oil control solenoid inside the pan. They also re-gasketed the oil cooler and the oil thermostat cover in the cooler. Intake off for the coupler, then valve cleaning.
So they’ve had a lot of the car apart… I didn’t do much digging or driving because it seemed odd and I just wanted to get it back to them.
I don’t have the car right now to try driving it differently, but in this test, I basically didn’t hit the gas very much because I was strictly monitoring how quickly the coolant was getting hot. The oil still seemed to get hot in about eight minutes.. they were just drastically different.
no codes. Fan is working. Intercooler pump seemed to be working. The thermostat did not open up at 197° though…. so I was unable to check flow through the radiator or drive it enough to maybe force any air out of the radiator.
so, Cali, you look at this as slow oil heating versus extremely fast coolant heating? Solenoid is plugged in right now due to warranty work, but historically temps were always much closer regardless of solenoid...
I’ve just never seen coolant get to this temperature by the time I pulled out of my neighborhood.
Your engine was just released after extensive service.
Now coolant heats up way too fast.
I understand your legit concern for a low coolant "bubble" issue...
-- Are the engine COOLANT + OIL LEVEL okay, now?
-- You're saying coolant heats up too fast... is tstat trusted or lazy getting stuck ?
ECU has a close monitor on tstat for defective temps.
This is "normal stock" :
Switching oil pump solenoid back to stock with 0/5W-40 could be confusing the mapped Tstat logic.
You can see cooling temp shooting up with oil doing nothing.
The key is coolant temp should go flat after tstat opening not keep climbing.
🤞
Last edited by CaliBenzDriver; Jul 2, 2025 at 02:47 PM.
Your engine was just released after extensive service.
Now coolant heats up way too fast.
I understand your legit concern for a low coolant "bubble" issue...
-- Are the engine COOLANT + OIL LEVEL okay, now?
-- You're saying coolant heats up too fast... is tstat trusted or lazy getting stuck ?
ECU has a close monitor on tstat for defective temps.
This is "normal stock" :
Switching oil pump solenoid back to stock with 0/5W-40 could be confusing the mapped Tstat logic.
You can see cooling temp shooting up with oil doing nothing.
The key is coolant temp should go flat after tstat opening not keep climbing.
🤞
Thank you for this input.
Tstat has maybe 10k miles. It did stay flat at 197-199 on a quick 4mi loop. Coolant was full, very full, higher than I keep it. Without knowing how high they filled it its hard to tell if if was just temp expansion or them leaving a bit extra for the inevitable air bubble or fluid not flowing. Yes they vacuum the coolant for filling but ive never found that to be 100% once a few days pass. Oil and low temp circuit I did not check. I honestly just wanted them to check before I got into it. Ive never really monitored my tstat since ive never seen any cooling issues. And taking it back to the dealer their first question was did the coolant light come on and I said I was not waiting till that happens cause once these are hot, they are HOT. The variable of the oil cooler being rebuilt/sealed makes me wonder if there was a failure of the internal oil temp stat when they replaced the leaking cap. The touched a lot, and maybe its normal but the last thing I want to do is blow up my cooling system during all this heat.
When you say "You can see cooling temp shooting up with oil doing nothing." Thats not something I ever experienced at least not to this differential. Unless its literally just confused. It was not confused before taking it in. I drove a few weeks plugged in and with reg oil.
Has anyone ever seen their car coolant heat so quickly from first start in the morning, four minutes to 190+ degrees with oil temps still at 120ish? ambient was 77, oil temp started basically there.
Last edited by Baltistyle; Jul 2, 2025 at 03:26 PM.
Tstat has maybe 10k miles. It did stay flat at 197-199 on a quick 4mi loop. Coolant was full, very full, higher than I keep it. Without knowing how high they filled it its hard to tell if if was just temp expansion or them leaving a bit extra for the inevitable air bubble or fluid not flowing. Yes they vacuum the coolant for filling but ive never found that to be 100% once a few days pass. Oil and low temp circuit I did not check. I honestly just wanted them to check before I got into it. Ive never really monitored my tstat since ive never seen any cooling issues. And taking it back to the dealer their first question was did the coolant light come on and I said I was not waiting till that happens cause once these are hot, they are HOT.
The variable of the oil cooler being rebuilt/sealed makes me wonder if there was a failure of the internal oil temp stat when they replaced the leaking cap. The touched a lot, and maybe its normal but the last thing I want to do is blow up my cooling system during all this heat.
When you say "You can see cooling temp shooting up with oil doing nothing."
Thats not something I ever experienced at least not to this differential. Unless its literally just confused. It was not confused before taking it in. I drove a few weeks plugged in and with reg oil.
Has anyone ever seen their car coolant heat so quickly from first start in the morning, four minutes to 190+ degrees with oil temps still at 120ish? ambient was 77, oil temp started basically there.
Granted your heat rise 4mn to 190F then flat does seems kind of quick.
This is inching towards being normal stock:
Your Tstat is only 10kMi... good!
Temp climbs up in 5mn then flat
Coolant tank level is normal
Oil pump is running MOD-0.
The oil heat-exchanger has been worked on. Can the dealer tech have flipped that gasket... unlikely/not possible right?
++++ DEALER STOCK EXPERIENCE :
you can trust the dealer experience with STOCK ENGINE SETUPS...
What does dealer say about "4Mn to 190F" ??
Last edited by CaliBenzDriver; Jul 2, 2025 at 04:46 PM.
Unfortunately, no word from the dealer today. They were extremely busy and I kind of just walked in and said hey I’m leaving my keys…. Lol
I’m sure they also wanted it to cool down completely before they test drove it.
i’ve never personally taken this model of oil cooler apart, so I’m not sure if they flipped any seals or if anything like that is even possible. my hope is they can check circuit pressure and oil pressure in various places..
Tstat has maybe 10k miles. It did stay flat at 197-199 on a quick 4mi loop. Coolant was full, very full, higher than I keep it. Without knowing how high they filled it its hard to tell if if was just temp expansion or them leaving a bit extra for the inevitable air bubble or fluid not flowing. Yes they vacuum the coolant for filling but ive never found that to be 100% once a few days pass. Oil and low temp circuit I did not check. I honestly just wanted them to check before I got into it. Ive never really monitored my tstat since ive never seen any cooling issues. And taking it back to the dealer their first question was did the coolant light come on and I said I was not waiting till that happens cause once these are hot, they are HOT. The variable of the oil cooler being rebuilt/sealed makes me wonder if there was a failure of the internal oil temp stat when they replaced the leaking cap. The touched a lot, and maybe its normal but the last thing I want to do is blow up my cooling system during all this heat.
When you say "You can see cooling temp shooting up with oil doing nothing." Thats not something I ever experienced at least not to this differential. Unless its literally just confused. It was not confused before taking it in. I drove a few weeks plugged in and with reg oil.
Has anyone ever seen their car coolant heat so quickly from first start in the morning, four minutes to 190+ degrees with oil temps still at 120ish? ambient was 77, oil temp started basically there.
never, something is not right until proven otherwise in this situation.
never, something is not right until proven otherwise in this situation.
i have never seen this
Thank you for chiming in. I agree. Since ive had not been in the car for a few weeks and so much was done I just didnt want to think it was my imagination. Ill be on the phone at 730 am when they open to make sure they drive it before the heat of the day. I really think its a bubble but time will tell. If it was me that did the work I would have gone out floored the hell out of it to try to activate thermostat but being a warranty and dealership repair, I dont want any liability.
Thank you for chiming in. I agree. Since ive had not been in the car for a few weeks and so much was done I just didnt want to think it was my imagination. I'll be on the phone at 730 am when they open to make sure they drive it before the heat of the day. I really think it's a bubble but time will tell. If it was me that did the work I would have gone out floored the hell out of it to try to activate thermostat but being a warranty and dealership repair, I dont want any liability.
rather, this engine is notorious for how LONG it takes get to normal operating temp (white), several threads on this as you know
Yep. Ive always found cooling very sufficient and in anything but hot weather, coolant would take a long time to get up to temp. Ive read that thread. I dont so much think the oil heat timing has changed so much as the cooling. As you mentioned, Ive not really found anyone with this same problem. Standard reasons would be thermostat, fan, water pump, intercooler pump, blockage. I dont seem to fit those reasons as discovered yet.
Once the engine has been re-checked by sce dealer,
I'd try pumping coolant by driving at higher Rpm, like 2000Rpm
5th gear at 30mph...
I understand the feeling that this is stock behavior, but this is not how my car acted when stock…partially why I’d like some people to chime in to see if their cars do this in stock form.
Today’s drive to the dealer was all under 2000 RPM. I was really not trying to have any influence from combustion on the coolant. Yesterday when I picked up the car, I noticed it get hot right away and did try various RPMs just not flooring it for more than a couple seconds. What I was not witnessing was upon lifting the gas pedal or on deceleration down the hill where the wind should’ve been helping cool the coolant.. so either the coolers aren’t taking away the heat or the oil isn’t taking away the heat. I really should’ve gotten into xentry before I turned it back over to them.
I also wonder if cleaning the valves had anything to do with this and it needs some time for adaptation
Ok, you know there's one failure condition that can cause real fast heat up...
You said the solenoid harness inside the oil pan was worked on by MB dealer tech, right?
Stock enabled solenoid should now be switching Low/Normal pressure at startup then above 3500Rpm.
-- Did they replace a new solenoid that had not been working
or is this original solenoid with new harness?
-- Your engine type don't happen to read oil pressure, right?
-- Does engine idle normally smooth/wet or extra vibrating /dry ?
Last edited by CaliBenzDriver; Jul 2, 2025 at 10:02 PM.
Ok, you know there's one failure condition that can cause real fast heat up...
You said the solenoid harness inside the oil pan was worked on by MB dealer tech, right?
Stock enabled solenoid should now be switching Low/Normal pressure at startup then above 3500Rpm.
-- Did they replace a new solenoid that had not been working
or is this original solenoid with new harness?
-- Your engine type don't happen to read oil pressure, right?
-- Does engine idle normally smooth/wet or extra vibrating /dry ?
solenoid harness only based on the parts description. Never had any issues with the solenoid.
no, engine does not read oil pressure natively
engine started and seemed very smooth. A little almost in perceivable shake on idle down, but I think that is due to the adaptation to the new clean valves. Drove very smooth. No perceptible lspi.
Should be picking it up soon. They flushed coolant again and do not notice anything that looks abnormal to them at this point. One suggestion is that the newer coolant is keeping the car hot for efficiency, which has been discussed before..
When first receiving the car back, I noticed there was a little bit of residue that was not blue so I had asked them what type of coolant went in and had them double check to make sure everything was correct. The new coolant was a regulatory required change and Mercedes now says it is OK to mix new coolant with blue coolant as well as just use the new G40 coolant. I had them provide me the documentation and I’m providing it here for awareness.
so I’m wondering, is anybody here on exclusively G40 coolant?
This is actually posted right inside the door to their shop.
solenoid harness only based on the parts description. Never had any issues with the solenoid.
no, engine does not read oil pressure natively
engine started and seemed very smooth. A little almost in perceivable shake on idle down, but I think that is due to the adaptation to the new clean valves. Drove very smooth. No perceptible lspi.
I think you should be golden with this service. You may want to re-learn stock heat Mgt with Rpm.
Fact: at 1000.Rpm hardly any pumping can happen!
> TEST DRIVE OK?
-- Do a warm-up test drive keeping up engine near 2000.Rpm with paddle shifters.
This will help pump the coolant all around.
-- Oil has no chance to pickup any pistons heat.
MOD-0 cylinders are kept unsprayed below 3000.R
-- So cold oil is only warmed up by coolant through the heat-exchanger.
Always keep an eye on levels of both COOLANT + OIL before starting with engine cold. Engine may develop leaks.
+++ MOD-0 STOCK HEAT REMOVAL...
-- Cylinders heat is exclusively managed by coolant circulation through smart-Tstat.
-- The energy-efficient water pump Rpm needs to be kept up 1750.Rpm for effectiveness.
Last edited by CaliBenzDriver; Jul 3, 2025 at 02:55 PM.
Test drive was great. They flushed it just in case but they also had another M157 engine in there that acted the same. However, today I did notice that the radiator fan was roaring in the heat, which I specifically did not notice yesterday so I’m thinking it was perhaps a bubble and new coolant.
As for RPMs, I never ever drive in low RPMs in general (paddle shifting is my go to in sport plus at start) so as to have all the benefits you speak of. The low rpms were a just in case…After I give it a good shakedown I’ll be back on the solenoid 5/50 train.
Test drive was great. They flushed it just in case but they also had another M157 engine in there that acted the same. However, today I did notice that the radiator fan was roaring in the heat, which I specifically did not notice yesterday so I’m thinking it was perhaps a bubble and new coolant.
As for RPMs, I never ever drive in low RPMs in general (paddle shifting is my go to in sport plus at start) so as to have all the benefits you speak of. The low rpms were a just in case…After I give it a good shakedown I’ll be back on the solenoid 5/50 train.
Thanks everyone for chiming in.
Congrats, love happy-endings! Good dealer Sce in the end...
The fan roaring means temp sensor at rear of Bank2 has heat. Keep up Rpm to circulate coolant around heads.
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