1986 300SDL --- Heat causing acceleration issues? - PeachParts Mercedes-Benz Forum

daw_two · #1 08-14-2007, 07:23 AM

My 1986 300SDL was worse than ever yesterday afternoon --- the temperature was 103

. It definitely had a LOT less acceleration than on previous afternoons when it wasn't so hot. Yet, I am sure when I get in it this morning at 7:15am CDT to drive to work, the acceleration will be back to what I believe is normal.

Facts:
I have not adjusted the ALDA, nor removed the EGR, nor done anything to this car since I purchased it.

0-2500 RPM takes probably TWICE as long as when the outside ambient temperature is cooler.

Questions:
Should I be looking at fuel delivery system?
Should I attempt to adjust ALDA?
Should I look at EGR?
Where do I start?

It's quite a dangerous feeling when I go to pull out into traffic and I have to second guess myself about if I have enough time. Hate that feeling.

HELP!

pawoSD · #2 08-14-2007, 07:33 AM

I think its partly because of less oxygen in the air once it gets so hot out. Less oxygen means less acceleration/power. I notice this when its over 85 outside too....my 617 just feels lethargic. When its about 5F outside....and the engines running at operating temp.....I can take off like no tomorrow. Tons of oxygen in cold air....

Thats my guess....maybe I am wrong. I am sure others will chime in.

bustedbenz · #3 08-14-2007, 11:45 AM

At least yours will stay running when it's that hot. Mine's lethargic in the heat too, with the added bonus of shutting down about every fourth or fifth time you let it idle from high rpms (slam on brakes, etc)

TX76513 · #4 08-14-2007, 11:49 AM

Quote:

Originally Posted by bustedbenz

At least yours will stay running when it's that hot. Mine's lethargic in the heat too, with the added bonus of shutting down about every fourth or fifth time you let it idle from high rpms (slam on brakes, etc)

Odd that you brought that up - mine did that this weekend after pulling off the interstate. Went to idle and thump -

no more engine running. It did start back up and has not repeated. SDL's the love and hate realtionship

bustedbenz · #5 08-14-2007, 12:04 PM

That's exactly what mine does. Slam on brakes, accelerate in stopped Interstate traffic to move up a few feet and then idle again for another minute or two... it just heatsoaks and gets worse. Hit the end of an on-ramp? Clunk, and it's dead.

Mine has never failed to restart instantly but it's sure unnerving when it does it in traffic - like, city traffic, where mine loves to do that.

Especially now that my starter seems to be headed south

patbob · #6 08-14-2007, 12:11 PM

THere's certianly less air in a given volume, and therefore less O2, but if that were the cause, you'd be seeing clouds of black smoke out the back from all the unbrunt fuel.

THere's a lot of things all reducing performance at once from thinner oil (more blowby) to less dense fuel, but the biggest drag on an engine's performance has gotta be the AC.. and it'll be a bigger drag the hotter it is out.

When it hit 102F here a while back, I noticed absolutely no difference in performance, but then I aslo didn't run the AC either.

Hatterasguy · #7 08-14-2007, 01:33 PM

Cars make a lot less power when its that warm. So you will feel a bit of a loss, however its not that noticable.

When its that warm you really need an iced down intercooler.

The ALDA could probably be adjusted a bit.

#8 08-14-2007, 01:37 PM

If you are down on power to the degree that it is THAT noticeable, it must be something other than heat-related.

Sure you'll lose a little power w/ high temps, a little more if the A/C compressor is engaged, but it should under NO circumstances be enough to make you nervous about pulling out into traffic!

Check the usual suspects - fuel delivery (filters) and throttle linkage, then report back.

Brian Carlton · #9 08-14-2007, 05:40 PM

Quote:

Originally Posted by Hatterasguy

Cars make a lot less power when its that warm.

Care to elaborate on how you come to that conclusion for a turbocharged diesel engine? You are on a diesel discussion forum.

Does the engine get less fuel from the IP when it's 102F. versus 30F?

Does the engine have sufficient air at 102F. for the fuel that's delivered to the cylinders?

What's the increase, in percent, for the IAT in 50F. ambient versus 102F. ambient? Does it matter?

Maybe you should ponder these questions before answering so quickly.

Hatterasguy · #10 08-14-2007, 08:44 PM

Quote:

Originally Posted by Brian Carlton

Care to elaborate on how you come to that conclusion for a turbocharged diesel engine? You are on a diesel discussion forum.

Does the engine get less fuel from the IP when it's 102F. versus 30F?

Does the engine have sufficient air at 102F. for the fuel that's delivered to the cylinders?

What's the increase, in percent, for the IAT in 50F. ambient versus 102F. ambient? Does it matter?

Maybe you should ponder these questions before answering so quickly.

Because hot air makes less power, less dense. Run a 1/4 mile on a 70 degree day vs a 100 degree day, you will lose a few tenths. Well at least with a gas car, na or forced induction. A diesel should act similer. The queston is whether you will notice it driving around town, which I doubt.

Noticed you were running B100, maybe its a fuel issue.

Do you have any suggestions Brian?

daw_two · #11 08-14-2007, 10:03 PM

Well, yes, it is B100. But it is the same fuel that has been in there for a week.

I should check my fuel filter(s); however, try to explain to me why it drove fine this morning if it might be clogged fuel filter.

tstarr · #12 08-14-2007, 10:38 PM

I found very noticeable degradation in my acceleration on the 87 300SDL under two circumstances - engine getting hot (usually when the weather was very hot) and while running B100. It was funny, but I didn't have a problem running B100 in the 82 300SD, but it was a real drag in the SDL. B20 or so is great, but full BD really bogs it down. As soon as I put a tank of dino diesel in, it pepped right up. I thought I heard that sometimes the IP needs to be adjusted for B100, but don't know. I just run the lower grade in it and it's fine now.

daw_two · #13 08-15-2007, 07:15 AM

Quote:

Originally Posted by tstarr

I found very noticeable degradation in my acceleration on the 87 300SDL under two circumstances - engine getting hot (usually when the weather was very hot) and while running B100. It was funny, but I didn't have a problem running B100 in the 82 300SD, but it was a real drag in the SDL. B20 or so is great, but full BD really bogs it down. As soon as I put a tank of dino diesel in, it pepped right up. I thought I heard that sometimes the IP needs to be adjusted for B100, but don't know. I just run the lower grade in it and it's fine now.

Hmmmm....Well, that would be easy enough to try today. The engine is hot, but I don't think it is overheated. The engine temperature gets right to 100 and then will cool off a bit once I start moving.

HEY!!! Would having the lower engine "cover" off have any type of impact on engine temperature or acceleration? I recently change my oil and had the lower cover off --- cleaned it really, really well and before I put it back on; I want to get my engine cleaned.

Any thoughts????

Hatterasguy · #14 08-15-2007, 12:24 PM

Well supposidly the belly pans help everything cool better. But I havn't had mine on and years and have never had a problem.

I'm out of ideas I have never ran into this problem. I'm trying to think what would be affected by heat enough to cause lower power. The only thing I can think of is fuel. The turbo system shouldn't really care what temp the engine or the air is. The ALDA is for altitude.

I suspect its fuel related, I'm just not sure what it could be.

Just for the heck of it block the EGR, you should get rid of it either way. Maybe its getting hot and sticking??

Notice any more smoke?

daw_two · #15 08-15-2007, 01:47 PM

No or very little smoke. Primary fuel filter is clean as a whistle. It drove find this morning and at lunch time like it has the past days --- it's always in the afternoon. Car is not any hotter; maybe a degree cooler since I get the shade from the little oak tree between 3 and 5 pm.

We will see what the drive home after work brings.