Mixing gas w/diesel for cold start?
 

In spite of new glow plugs, my 1985 300D will not start when the temp drops to around 20 degrees F overnight. Block heater is out of the question as I live off-grid. My buddy who drives a VW Rabbit says that VW recommends mixing up to 25% gasoline in the wintertime. I'm wondering if this will work on my Benz? I sure don't want to do it if it will damage the engine or fuel system. Anybody got any input on this? Thanks.....Dave

It was about 32 here the other day and my 76 300D started up 1st try and only took 2 turns of the motor. Check those glowplugs again and make sure all 5 are working and also check the relay.

I drive an 85 as well and I had the absolute pleasure of trying to start my car with a sub zero temperature at 2 am.
I'm going to cut and paste what I wrote in a thread over at benzworld. I doubt gelling diesel is your problem.

Good luck man. Those are really the only things needed to get our w123s going!

Valves
 

I just did a valve adjustment on my TD for the first time. A whole different car! Starts right up without all that smoke it once had. I also bought a new battery. Glow plugs tested fine but I did pull them and ream.

So do a valve adjustment ;)

I remember years ago in PA when an MB tech advised NOT to do this on my 300TD... because of risks and detrimental effects. Fuel pump or injection failures were some of the problems he encountered. Combustion temps get raised and cetane rating lowers as well, and I'm sure there are other reasons against it... so in the end, I wouldn't risk it IMO.

Merecedes owner's manuals (Mine's from 1980) used to suggests adding up to 50% kerosene or up to 30% regular unleaded gasoline in very cold temperatures, if #1 diesel was not available. I don't know when they stopped recommending it. Steve

I heard the "very cold temperatures" recommendation was based on -10 degrees Fahrenheit which equates to approx -23 degrees Celsius :eek:
Obviously to combat against the extreme cold temp's gelling effect.
At these frigid temps, battery and glow plugs must be 100% up to snuff at a minimum.

I guess this is one of the challenges of living off-grid that hasn't been in the press. One thing you can do is to remove the battery and take it inside so it stays warm until you need it to start the car. Batteries lose much of their power when they are cold.

20 degrees is not cold enough to cause fuel problems. Do some more checking on your glow plugs and if they check out, do a compression test. 20 degrees should not be a problem on a relatively healthy engine with functioning glow plugs.

I live off grid too and in North Dakota so my diesels have had to be started on some really cold mornings with no block heaters.
What works for me is to make absolutely sure all glow plugs are working perfectly, engine is tuned perfectly, valves etc, battery is the highest capacity I can fit under the hood and when it's really cold I keep it in the house until I need to start the car. Synthetic oil has made a huge difference in cold starting as well. When I am away from home I just leave the car running, sometimes for days at a time but that's when it's well below zero. I have run my 500,000 mile 300SD at -58 below zero, with almost -90 below zero wind chills, the secret to starting it when it's that cold is to start a fire under the oil pan. In my garage I have a pit for oil changes etc, and I have a wood stove down in the pit so when I want to go somewhere I go out with an armload of kindling or sticks and start a really hot fire in the stove, which is directly under the car when it's parked in the garage, in about 20 minutes I can run the defroster without even starting the car and of course, with the engine plenty warm it starts just like a summer day. For when I am not parked in the garage I have one of those propane weed burner torches that I keep handy, light this and carefully place under the engine so it doesn't melt any electrical or rubber parts, in about 10 minutes both the oil and the engine are warm enough to start perfectly, even at -20 below zero and an added benefit is the transmission gets a bit of heat too. I have used gasoline in the diesel mix to keep the fuel from jelling but I prefer mixing kerosine. Usually I just run #1 fuel with an additive for lubricating.

Those are great tips for people that live where it gets -20F and colder, but the OP lives in Arkansas. I highly doubt gelling fuel is his issue. The OP needs to check his glow plugs first (that means check to make sure they are all getting voltage as the fuse strip could be broken), then valves, then oil weight, then battery.

One way you can check for gelled fuel is to use the primer pump. If fuel is pushing through the system for a minute or so of pumping then fuel gelling is not the issue.

PS- I really enjoyed reading your stories about getting them started with no block heater in frigid temps. :o

While I doubt 'gelling' per se is his main problem....

I do not think that 20 percent gasoline mixed with his diesel will do any harm since , as Sbean mentioned, it is stated in the owners manuals of these cars as helpful for cold weather.

A lot of things go into the engine starting... and with cold weather the combo of lots of things not being at their original specs can cause the need to help an engine with other changes in the overall picture.

PowerService = Cetane boost = easier starting/smoother running plus gel protection, though I agree not his problem. That and basic maintenance will probably solve most of the problems. Pouring boiling water on the block is a new one to me - sounds like it would work but I would hate to pour it then have it freeze back up since its so cold!

Pouring boiling water on cold cast iron is a TERRIBLE IDEA...
DO NOT DO THAT !!!!!

not just the block ... but even less hot/cold shock could damage the injection pump...
just forget this idea and warm the water inside the block...

I've read where some people will remove the motor oil through the dipstick tube and preheat it in the house before they need to start the engine. Just don't forget to put the oil back in the crankcase.