Normal IAT's for the M275
Thread Starter
Newbie
Joined: Dec 2025
Posts: 8
Likes: 0
2012 S65 AMG
Normal IAT's for the M275
I'm chasing high IAT's on my 2012 S65. Hooked up a scanner on a 75 degree day and IAT's were around 140F-160F cruising around at 50 MPH, and would go up to 180F when idling. Obviously way too hot, starting with a new intercooler pump and hopefully that will fix it. I have seen people say the cooling system is inadequate on these, but what is a typical spread from ambient air to IAT on these? The car still runs normally, no check engine light or anything so I'm not sure how long it has been in this condition.
MBWorld Fanatic!
Joined: Feb 2012
Posts: 2,608
Likes: 1,208
From: Phoenix
222 S-65
It won’t turn on a check engine light for high IAT. It pulls timing and boost. Getting all the air out of the charge cooling circuit is challenging at best.
As for what normal IAT is... I have never measured.
As for what normal IAT is... I have never measured.
Member
Joined: May 2020
Posts: 247
Likes: 57
From: Fort Worth
2005 CL55 AMG || 2005 CL65 AMG || 1989 560SEC
I believe mine are about +40 to 55f over ambient while cruising. On decel and while idling the temperatures spike, which is normal.... airflow is just too slow with the throttle plate closed to effectively move air across the intercoolers. Temps go down pretty fast once you start accelerating from a stop, something like 3-6 seconds at normal acceleration.
There's a few threads on IAT's for the v12's, and a healthy system should be in the range I mentioned. If your pump is weak or dying your temps will be higher. IIRC the computer starts to pull timing around 60-65 Celcius.
Clogged air filters will raise temps as well.
I was able to bleed my system after replacing the pump by filling the tube that ran to the pump then re-attaching it (clamped the other one that comes down from higher in the engine bay), then filling the intercooler system by disconnecting other hoses that had air in them and doing the same... I think the soft hose on the right side of the engine that runs down got filled next, then I filled from the top main fill point till fluid came out of the metal portion the just-filled tube attached to and reconnecting. Once I got there, the pump was able to move air around the system, and I just topped it off over the next week or two after air migrated to the top of the system.
There's a few threads on IAT's for the v12's, and a healthy system should be in the range I mentioned. If your pump is weak or dying your temps will be higher. IIRC the computer starts to pull timing around 60-65 Celcius.
Clogged air filters will raise temps as well.
I was able to bleed my system after replacing the pump by filling the tube that ran to the pump then re-attaching it (clamped the other one that comes down from higher in the engine bay), then filling the intercooler system by disconnecting other hoses that had air in them and doing the same... I think the soft hose on the right side of the engine that runs down got filled next, then I filled from the top main fill point till fluid came out of the metal portion the just-filled tube attached to and reconnecting. Once I got there, the pump was able to move air around the system, and I just topped it off over the next week or two after air migrated to the top of the system.
Last edited by JustTXn; Dec 27, 2025 at 04:12 PM.
Senior Member
Joined: Feb 2014
Posts: 268
Likes: 47
From: DFW
2006 C55
My 13 CL65 also runs 140-150 F on a typical day. I installed a higher flowing pump and the only real change was a quicker recovery from the highest spikes.
I have also installed the updated IC reservoir but that doesn't really pact performance after the system is bled.
In all, it's rather disappointing.
I have also installed the updated IC reservoir but that doesn't really pact performance after the system is bled.
In all, it's rather disappointing.
Member
Joined: May 2020
Posts: 247
Likes: 57
From: Fort Worth
2005 CL55 AMG || 2005 CL65 AMG || 1989 560SEC
I think weistec and VRP both sell a kit, VRP's goes on sale occasionally. It's on my to-do list, might seal and repurpose my washer fluid reservoir since they slowly leak in both of my 215's, and replacing the pump grommets did not fix the issue.
MBWorld Fanatic!
Joined: Feb 2012
Posts: 2,608
Likes: 1,208
From: Phoenix
222 S-65
The Weistec kit looks like a common controller and pump in a reservoir they made up for too many dollars. Search for Water/Methanol for diesel trucks to save $800.00 with a bigger reservoir.
Trending Topics
Super Member
Joined: Sep 2021
Posts: 534
Likes: 115
From: Ann Arbor, MI
2004 SL600
My IAT runs also about 40F over ambient while cruising on the highway. Its a bit higher in city driving and higher yet just sitting. I have a higher volume pump and made my own equipment to get the air out of the system.
IMHO, if you are running 60F+ while cruising, you are air in the system or a problem with the pump or plumbing.
My winter project is to add an A/C chiller to intercooler fluid system.
IMHO, if you are running 60F+ while cruising, you are air in the system or a problem with the pump or plumbing.
My winter project is to add an A/C chiller to intercooler fluid system.
MB World Stories
The Best of Mercedes & AMG
Manual Mercedes? 6 Times Sindelfingen Let Drivers Have All The Fun
Verdad Gallardo
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Verdad Gallardo
8 Classic Boxy Mercedes Designs That Have Aged Like Fine Wine
Verdad Gallardo
Flawlessly Restored Mercedes 190E Evo II Heads to Auction
Verdad Gallardo
Electric Mercedes C-Class Unveiled: 11 Things You Need to Know
Verdad Gallardo
Mercedes EQS Gets A Major Update: Everything You Need to Know
Verdad Gallardo
5 Underrated Mercedes-Benz Models That Don't Get the Love They Deserve
Verdad Gallardo
Mercedes 300D Has Pushed Well Past 1 Million Miles and It Ain't Stopping
Verdad Gallardo
10 Most Reliable Mercedes-Benz Models You Can Buy Used
Verdad Gallardo
Thread Starter
Newbie
Joined: Dec 2025
Posts: 8
Likes: 0
2012 S65 AMG
For anyone who reads this later, problem solved! I ended up having the intercooler reservoir and parts from the M279 installed, there is a post or 2 about it here. Then the system was properly bled and runs great now. IAT is around 40-45 degrees celsius cruising on the highway on a 75 degree day and performance is so much better.
