300SDL and 300SDL Transmission Lockout Function
 

I have noticed that my 1986 300SDL is sluggish in cold weather (below 40 degrees F) and will not accelerate or readily change gears until the car has run for several minutes - after that, the car runs well. What is happening? Is there a switch from a time delay/thermal relay that enables the car to change gears after it warms up?

When I first bought this car used from a dealer, the car would not switch gears at all and remained in low gear during cold weather. I refused to buy it until the dealer fixed the problem. The dealer supposedly replaced a switch in the car and since then the car fuctions well after it warms up - whereas it woudln't switch at all when I got it.

I sent another thread earlier today asking about my 1990 350SDL
because it had been running well and suddenly would not switch gears. Is there a fuse link that enables/disables this lockout function?

Marvin Smith

No upshifts at all -- stays in first (or second) no matter how fast you drive?

Busted governor gear from a disintegrated check valve, not a bad fix, but not free.

Otherwise, a valve body problem made worse by thick tranny fluid, I would guess.

There is a cold engine shift softening control on my 300D, but that won't change the shift points.

the 603 IS sluggish cold -- until the combustion chambers warm up, output is low. Drive gently until the temp guage moves, nothing you can do about it since it won't warm up much just idling. I let mine idle until it runs smooth, then drive about 20 for the first half mile or so.

Peter

Sluggish 300SDL
 

Thanks a lot for your prompt response. I've driven the car slowly until it warms up and it runs fine. I thought maybe something could be done to minimize the need to warm up the engine.

Marvin Smith

Living in the tropics might help!

No, just a characteristic of the engine. Worse on the 603 than others. My Volvo TD doesn't show this any where near as much, but it has a cold start timing advance, and driving hard cold tends to wear out the upper cylinder walls from excessive pressure from advanced timing if you routinely floor the engine cold.

Just don't pull out in front of a fast moving semi and expect to get away it driving a dead cold engine.

Peter

mine is similar
 

Marvin,

Below 30*, maybe 25* my car will not shift from 2-3 until above 3000 rpms when first started. As said above, after about 1/2 mile it shifts normally.

In addition there is a cold shift "softener" feature that makes the transmission shift more slowly (but at the same speed). This was causing a shift/rpm flare for me coming up a large hill every morning. I disconnected the wire (attached to the thermostat housing on the passenger side) as recommended by others here. It now shifts more firmly and no flares when cold.

Now that it is warmer, it is back to shifting as usual.

Chuck

transmission softener
 

You've answered my question pertaining to a transmission lockout completely - it's called a transmission softener.

Many thanks,

Marvin Smith