300D fuel economy questions

I just purchased an 80 300D and it purrs but my mileage is worse than I was getting on my 300SD.
There is no particular smoking problem, it starts easily but I am only
getting 22MPG on the highway while holding steady at 65.
I was expecting closer to 30 MPG.
Any suggestions?
--

Roger Shoaf

About the time I had mastered getting the toothpaste back in the tube, then
  Click to see the full signature.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Roger Shoaf wrote:

I feel your pain. I was expecting ~31mpg on my '92 300D but I average 26. If I don't use a cetane booster it gets worse, as low as 23. I run 17" wheels with 225/45 tires which probably have higher rolling resistance than the stock 15" but I keep the tire prx a skosh high.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I think something is wrong with your car. You should check your injection pump, and the chassis alignment. The engine compression should be good also. The car should give 32 mpg as the catalog says.
Good luck.
On Nov 7, 6:21 pm, JD wrote:

Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

My 300SD will get 27mpg at 65 IF i drive it easily. It drops like a stone to 24-25 when I kick it over 70. Ever notice when you put on the CC the accelerator seems to come up--almost like you are using too much foot to go the same speed? This may seem a little odd, but one of the things I run up against is my car is so quiet, I'm up to 80 mph before I know it. One of the regulars here gives the good advice to ck that the banjo fitting at the back of the valve cover isn't clogged. Ck that. Notice if you are going faster than you think since it's easy in these cars (My car's spedo says exactly what my GPS reads for speed. How is yours?). The ups and downs in speed kills mileage fast. It's worth getting CC fixed (if broken) for the gas savings you get with fewer radical changes in speed (on a flat road with light traffic at a reasonable speed). I know this sounds sophomoric, but ck the air filter, tire pressure, and for fuel leaks (the banjo bolt on top of the fuel filter housing is a bitch. DO NOT over tighten it). Let us know if you find anything that helps.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

How many miles on the injectors? If it's 125K or more the nozzles are due for replaement and that could be a factor.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Banjo bolt is the first thing I would check. Fuel filter needs to be changed... Compression checked if possible.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Isn't the banjo bolt only on the turbo models?
--

Roger Shoaf

About the time I had mastered getting the toothpaste back in the tube, then
  Click to see the full signature.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Yours is not a turbo?
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

No turbo, hence my disappointment with 22MPG. I figured I would be getting something for having a lot less HP.
The car starts and drives nice, no smoke and hums along just fine once you are up to cruising speed.
--

Roger Shoaf

About the time I had mastered getting the toothpaste back in the tube, then
  Click to see the full signature.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
If the engine runs good then I would do a couple of test... simple stuff...
If you put diesel fuel injector cleaner through the tank, does the fuel mileage increase? It should...
Tire pressure?
Check your brake to make sure it is not binding...
Check wheel bearing in front and make sure it is not hard to spin wheel.
Trans fluid level? I always suspect the high mileage tranny has some slips that affect the fuel mileage on diesel.
Air filter... is it new?
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

My 87, though a different engine, recently got 34mpg from Columbus to D.C., and it has > 222K on it. Since arriving in DC I have given it a purge, though not by my intent. (I stupidly put gas in the tank and had to siphon it out, refill and run the gas out of the system.) Since then it sounds much better and has a great deal more power. I might suggest on an older engine that you give it a good cleaning out, though by the recommended means.
Collin
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.