'81 300SD Why no power when cold? - PeachParts Mercedes-Benz Forum

tyl604 · #1 01-09-2009, 02:34 PM

Could someone 'splain me please why my diesel has so little power when I first start it up in cold weather. If I back down the driveway (decent hill down) then need to drive back up because I forgot something, it absolutely has not enough power to drive up the hill. I can put it in first gear and floor it and it will not move up the hill. After it warms up from driving, power is fine.

This does not seem to be a turbo problem because even cold I can speed up fine on the city streets. My guess is that as the engine warms up, the rings expand and provide more compression - and therefore more power; before that the compression is lacking and that diminishes the power.

Am I on the right track?

Thx

rrgrassi · #2 01-09-2009, 03:02 PM

Diesels require heat to run properly. As the car runs, heat increases as does efficiency. It should still pull itself up the hill though. Is your car trying to start from 2nd?

tyl604 · #3 01-09-2009, 03:22 PM

Second gear? Not sure. I put it in Low and try to get up the hill. Even with the pedal floored, the engine will hardly spin faster. It will spin in Neutral but not in Low. In fact I have even had to turn around and back up the hill, which works with difficulty; lower gear ratio I assume.

Interesting, I thought everyone would say they had exactly the same experience and this was a design characteristic of the 300SD.

pawoSD · #4 01-09-2009, 03:32 PM

There might be a fuel problem if its that weak when cold. Mine is "slow" when cold, but in first it still makes plenty of power to get up a slope....plus the "load" of going up a hill will build heat quickly and the engine will very quickly generate more power.

katja · #5 01-09-2009, 03:47 PM

I've wondered about this problem for a long time but hadn't noticed any posts about it before. My uncles '79 300SD behaved the same. But a neighbor's 300TD was even worse. Mind you, this was back in the early 80's when these cars were relatively new, so it's unlikely it was poor compression.

I've never known a W126 300SD to be that slow when cold, and my 240D (although with a manual transmission) is no slower than it is when warm.

johnathan1 · #6 01-09-2009, 03:45 PM

My 300D used to act the same way...i just always thought it was normal for diesels.

oldsinner111 · #7 01-09-2009, 03:47 PM

Sounds like tank screen,filters,weak fuel pump,or loose hand pump.

argus445 · #8 01-09-2009, 07:54 PM

Quote:

Originally Posted by tyl604

Could someone 'splain me please why my diesel has so little power when I first start it up in cold weather. If I back down the driveway (decent hill down) then need to drive back up because I forgot something, it absolutely has not enough power to drive up the hill. I can put it in first gear and floor it and it will not move up the hill. After it warms up from driving, power is fine.

This does not seem to be a turbo problem because even cold I can speed up fine on the city streets. My guess is that as the engine warms up, the rings expand and provide more compression - and therefore more power; before that the compression is lacking and that diminishes the power.

Am I on the right track?

Thx

Well i'm assuming it's like 20 degrees or something outside? If it's pouring out smoke and not making power it's eather compression or timing could be off. But until the engine block and such get up to temp it's basically a heat sink pulling heat from the chamber lowering the temp. making it alot harder to burn all the fuel. So if when your flooring it they're should be alot of smoke depending on amount and color u can determine if it's a fuel issue or just compression or heat issue.

LUVMBDiesels · #9 01-09-2009, 08:10 PM

What kind of fuel are you running? I could be thickening up...

tyl604 · #10 01-09-2009, 08:12 PM

I will have to think about this. First there is absolutely no problem with pickup on city streets even though the engine is very cold. As long as I am on a flat surface it speeds up fine, the turbo kicks in, and it accelerates OK; typical amount of smoke.

However when I am trying to get up the driveway hill and have it floored in Low, the engine does not rev high and there is not much smoke. I believe that I could engage the parking brake, shift to Neutral, and spin up the engine. But with it in Low the engine will not rev and I get no power; you can feel it strain to move forward without success.

If this were a filter or screen problem, I believe the problem would exist under different scenarios. But the only time this happens is when I am trying to get back up the driveway.

BTW this is not a problem that I want to fix; I only have a bug to know what causes it. As far as I know it has worked this way for 25 years.

oldsinner111 · #11 01-09-2009, 09:14 PM

Uphill trash going to screen.Thats what it sounds like.You have to be careful.Alot of people try and run SVO or WVO in a stock tank.The metal in the tank sheds years of diesel flim.At the same time svo or wvo coats the tank with another film.Then when fuels are changed problems.I battled that 18 months cause I was unable to remove tank and clean it.Power loss on hills was one problem.I was changing primary filters every 100 miles.

redassag00 · #12 01-09-2009, 11:37 PM

How steep of a hill are we talking about?

How many miles on the car?

MBNRA · #13 01-10-2009, 01:02 AM

Fuel filters and injection pump timing plus valve adjust and report back.

captainmonk · #14 01-10-2009, 01:56 AM

if the engine isnt speeding up arent we talking about a transmission problem?
mine is a real slow poke when first moving in cold weather
another thread has been discussing this

fruitcakesa · #15 01-10-2009, 08:57 AM

My 240d is also very sluggish on cold Vermont mornings. When getting up my steep short driveway, I often have to get a run at it. But once rolling it quickly achieves full power.
My filters are relatively new and tank and in tank strainer have been pulled and cleaned.