Diesel preventative/ maintenance - What checks are required?

[pcman_jh]

Folks,

My C250D has just dropped its MPG down to 37 MPG, this being the lowest I've recorded in the last 5 years - usually averaging 40.5MPG.

I know it could be caused by the start of the cold weather, which is seasonaly known to affect the consumption, but are there any checks or preventative mainenance advised. The car is a 1994 C250D (5 cyl non turbo), with 129,000 miles on the clock.

If it makes any difference, there have been experiments made over the last year with 25% Veg oil in the tank. The 37 MPG reading was taken on 100% diesel (but see further on) as my Veg oil experiments have been suspended for the moment. To my surprise the the current reading was also taken with STP diesel additive, which is supposed to clean the system, and offer better efficiency. Without the additive, could my MPG have dropped even lower (the next reading will tell, but I've still got 3/4 tank of fuel to get through over the holidays).

What about injectors being routinely replaced or cleaned?

Anything will be appreciated.

 

[dieselman]

Firstly I suspect the winter diesel to be causing an efficiency loss. My own car has increased its consumption recently in line with the weather.

Check all the usuals such as tyre pressures, binding brakes. My tyres were down 0.3 Bar due to the air cooling so contracting.

I have found my driving to be more stop start as traffic speds have slowed due to inclement weather so this will have an effect.