Twichel04

I'm getting some top end noise at idle that is a little concerning. It can best be described as a "diesel" sound, but not as loud as a diesel motor. I have read that is is "normal" for the c36, but I fear that it is only thought of as "normal" because it's a common problem with the c36. The noise seems to be coming mostly from the intake side of the head. It's not there when the motor/oil is cold, and the car seems to have more OOMPH when cold, but once it's warmed up, that diesel sound ALWAYS comes back, but it really only seems to be present under 1000-1200 rpm.

It doesn't seem to be hurting anything, but I really don't want to risk it, plus it's a bit embarrassing, lol. I feel like it's an oil pressure related issue. The car was seriously neglected prior to my acquisition. Cold starts on the car sound a little too "dry" to me. And the oil filter hadn't been changed in years. It had a lifter tap when I first got it in addition to the diesel sound. The lifter tap was fixed when I did the valve cover gasket. When I had the cover off, I cleaned the lifters as best I could, then changed the oil to 20-50. After that, the tap and the diesel sound went away completely.... however the diesel sound came back. But not the tap, thankfully. I have since changed the oil again, hoping that the sound would go away again, and it has not. This is starting to worry me.

Can anyone recommend a place to have the C36 head refreshed? I want to pull the motor at some point and give it a good going through. I can handle most of it my self but I'd really like someone who has experience and a good reputation with working with AMG motors to send the head off to.

Any suggestions?

Super B

Any way you could take a video? Always nice to actually hear the noise.

Twichel04

I'll try to make one tomorrow. I'll actually make two. One after a cold start when its quiet, and one after its warmed up.

Super B

Sounds good.

Twichel04

Ok, here are a couple quick videos.

Cold engine at idle. (sorry about the poor quality, I shot this with my phone and it was echoing in the garage)-


And hot engine at idle after driving around town all day. -

SbolenC36

I have almost the exact same issues with my 1995 c36. Loss of power when hot, diesel sound at idle, almost a "dry" sounding cold start, etc. I'll bet we read the same old threads about all this, most saying it was normal, etc.. Will definitely be following this thread for possible solutions. Thanks for bringing the issue back to the forefront

SbolenC36

With regards to the loss of power at hot operating temps, I read some threads stating that the "cool harness" and a lower degree thermostat helped to rectify the issue, simply by keeping the engine a bit cooler. Anyone have recent experience with this? Maybe the same fix would help cut down on our diesel idle sound since it only seems to be prevalent with a hot engine?

Twichel04

Tell me more about this "cool harness" ...That sounds like a must have in Florida, no matter what! haha.

Don't get me wrong, the car still has plenty of power after the diesel sound comes in, but there is definitely more available fun before the motor has reached full operating temp.

BenzMaster19

The C36 diesel sound is completely NORMAL. If you google C36 diesel sound you will quickly learn that it is completely normal and harmless to the engine. Owners have stated that their C36 was like that from new, they even went as far as contacting AMG in Germany and they also said not to worry about it, it's a normal part of the design of the engine. If I remember correctly, it's something to do with the advancing of the valve train mechanism and when the oil warms up the pressure changes on the mechanism and it starts the diesel sound. It's what you get when you purchase a hot rodded engine. I personally love it, it reminds you that you have a unique vehicle. And just a FYI, I would never run a 20W-50 weight as cold starts are going to be hard on the engine as it will be thick on start up. Stick with 5W-40 MB approved 229.5 ONLY.

Twichel04

I have heard that before, but I have also heard of people with C36's that have never experienced this issue. Plus the drop in power when the noise comes in is part of what leads me to believe that there is something wrong.

BenzMaster19

I real C36 engine will make the diesel sound, it's made that way. What some people don't realize is that previous owners can very well replace the engine with a regular C280 as it's impossible to visually tell. And regarding the drop in power yes, that is normal for the C36 engine aswell, the remedy? A 79 degree thermostat, but when it's really hot out it won't help unless you can find a way to turn those electric fans on earlier. And like I mentioned in my first post, get rid of the 20W-50! You need a lighter weight on start up so it flows easier on the cold starts.
What you've mentioned is classic C36 characteristics. Welcome to the C36 AMG

SbolenC36

Cool harness link: http://www.k6jrf.com/MB_S500.html

Info is about a 1/4 way down the web page. Scroll down and you'll see it!

Cool harness v2 is for our four pin connectors, it lowers the temperature at which the aux fans turn on. I believe its $90 plus $5 for shipping.

Twichel04

Yeah, I ended up finding that last night. I am probably going to make my own, along with an efan kit that I am planning on putting together and a lower temp t-stat. My goal is that, even in Florida, I can get the car to maintain an 80°C running temp. We'll see how that works out... You know how goals can be, haha.

SbolenC36

Haha I know the feeling. I'm in the same boat with the desert heat here in Phoenix. Pain in the butt trying to keep our 36's temp down in traffic. Your plan should do the trick

Super B

Speaking of t-stats. Mine gave it up the other week. Failed closed too.. Never overheated but ran hot.

But along those lines, if a fella ditched the clutch fan might free up enough space for another row on the radiator core then add a good electric fan. Might be a little on the expensive side but looks like there is enough room.

Twichel04

With the factory radiator in there, and the fan clutch removed, there is a hair over 3" of clearance in there for a puller fan. I really wanted a 2500CFM fan, but every single 2500 fan I found were all 3.5'' deep. I went ahead and ordered a 1750CFM fan that was 2.5'' deep. I am planning on mounting it to the original fan shroud if I can, so that it will be easily removable, for belt replacements, etc. I found a coolant temp switch that will kick the new fan on at 82*c and back off again at 76*c. Also adding a 79*c t-stat in there too. Now I just need to find out what resistor that I need to add to the factory coolant temp sensor to make the factory fans kick in at 90 or 95 instead of 105. That way, if there is a really hot day, there won't be too much of a gap before the other two kick in.

Super B

Nice work, shame the larger fan didn't fit. Thats why I was thinking of a extra capacity radiator and a large pusher.

For sure take some pictures. Im really looking forward to seeing what you turn out. Good luck on the garage shop btw.

BenzMaster19

Great work!! Keep us posted!!
I'm sure the mechanical fan delete will free up some HP too.

Sulaco

oh my goodness, yes. even my old C280 did this. in the winter on a cold morning, I could floor it from a dead stop and break both the back tires loose into an epic burn out. after it warmed up, the best I could get was a faint chirp. in the summer it just ran noticeably slower at all times.

Super B

Do you think it's related to heat soak into the intake/maf/IAT? or more if a tuning thing from the switch over to closed loop?

BenzMaster19

A combination of heat soak, a good reduction in torque from the way the intake manifold is designed when the engine is heat soaked/higher air intake temps, and retarded timing from the PCM as air intake temps and engine coolant temps and heat soak increases.

Twichel04

Well after many many hours of researching this topic, I will concede that this is indeed "normal" for the c36. HOWEVER, while I agree that it is normal, I do not believe that it is right. There is something inherent in these cars that causes this noise, and it has something to do with the cam, because the intake cam is where the noise comes from.

It has nothing to do with the timing advance though. I ran the car from cold with the cam solenoid disconnected, the noise came back. With the noise present, I manually activated and deactivated the timing solenoid, with no change.

I do believe that its just a "fact of life" with our cars and it is not anything broken, therefore it's nothing that can be fixed. But just because I can't fix it, doesn't mean that I can't prevent it from happening.

It seems to correspond to engine temperature. You guys already know my plans for keeping it cooler, the parts should be here Tuesday. I will report back after I get all that installed. I think it will help, but I am not sure if it will keep the noise at bay... But I have other ideas too..... Once I get the coolant to stay cooler, I think that the oil needs a reduction in temperature also, so an oil cooler is in the works (which I think that the C36 should have had from day one anyway).

I think that my cooling fan set up plus an oil cooler will help keep the temps down low enough to keep the sound away (or at least much quieter) and will help hold onto that power we all tend to lose after we get up to temp.