Any diesel mechanics have any facts to indicate if the additive is helpful in warmer weather?

I have a 240d and 300sd

 

Depends on what additive you mean. One for the engine to lower friction and heat. Another for fuel additive for injector and fuel tank cleaning.
I have used both types for 7 years in 3 diesel's. First, no damage or issues. Lucky , but I doubt it.
Exhaust clean whole time, no black exhaust bursts with load or strong acceleration.
My Audi, BMW and Jeep mechanics swear they are worthwhile as preventative measures. Travelled around 60k in each car to date.
I'll continue to use these, but only the brands that have research and history behind them.
Good luck.

 

You will find all kind of reviews about diesel additive. Placebo effect is strong with them, so I am always skeptic.
Those driving in cold climates love "Diesel kleen" (don't remember exact name).
The only proved to work is LM diesel purge, but that require disconnecting fuel lines.
Bare in mind that in last few years all US-sold diesel fuels have some % of bio, who is having cleaning values.

 

ULSD diesel has neither the lubricity or required cetane number for proper and reliable operation, especially where older diesels are concerned. This is primarily a North America issue, and even worse a Canadian issue where diesel fuel quality standards are voluntarily reported (with the exception of the sulphur content of course). I am not a mechanic myself, but grew up in a family of mechanics, and I've been working on cars most my life. Take that for what it's worth.

The diesel fuel itself, is the only thing that lubricates the high pressure pump, and in recent years there's been an increase in failures of these pumps across the board - this seemed to coincide with the switch to ULSD. Maybe just a coincidence.

The research shows that using a 2-EHN as a cetane improver at a dose rate of 250:1 ULSD:2-EHN provides approximately 10% improved fuel economy when the fuel has an original cetane number of 45.

Lubricity has always been an issue for diesel high pressure pumps, so clearly, a reduction in lubricity will exacerbate the problem.

As far as cold flow properties - here in Canada every fuel station adds an additive for this in the winter, or else you can't even pump it. Unfortunately, sometimes the additive is Kerosine, which further lower the cetane number and has less energy in it. Using non-treated fuel and adding in specialized cold flow additives will improve the performance of the fuel.

The placebo effect is a real thing. Most diesel additives are crap: about 5 - 10% 2-EHN and about 90% diesel fuel as a carrier oil. So in effect, with most additives you're just paying $20/l for mostly diesel fuel.

I have yet to find an additive whose recommended dose levels can effectively raise the cetane number to match their claims. For most consumer products, the real value is in the added lubricity.

. . . that's just my two cents . . .