Would fuel temp at 80C+ effect the IP internally?? (o-rings and other delicate bits in addition to the ongoing ULSD effects).

Why ask this question? I've just removed the fuel thermostat because it leaks and considering either a)direct run from prefilter to lift pump or b)prefilter to the heating circuit then to the lift pump. I do have a block heater installed(IDK if it works). Glow plugs work AFAIK. Now that I have the blower motor working I do plan on enjoying heat this winter...We did get a pretty cold winter last year but on average winters in Philly arent too bad and winter blend 'should' not gel until -15F.

Im thinking that I can just do a) and not worry about it. OTH should Philly get another cold winter, I'd like to be able to do b). Looking at the FSM, This circuit is intended to heat the fuel and make starting in cold weather easier/smoother. The fuel thermostat closes and redirects the flow away from the heating circuit and directly to the lift pump at 25C. With no thermostat i.e b), then the coolant temp would= engine temp = 80C+, which = fuel temp the lift pump/IP would be getting. If its that cold, I will be running the heater whenever driving

NOTE: Little bit of lite reading on effect of temp/pressure to diesel viscosity:approx 25C is the temp point with the most change in viscosity. Fuel #3 comes the closest to what I typically run: Diesel+PS Cetane boost.

http://www.mdpi.com/2227-9717/1/2/30/pdf)

As mentioned in the previous thread, if you get rid of the thermostat and run the fuel through the heat exchanger at all times, you will only be heating the fuel when your heater is turned on. In the summer with the heater off, you'll still have cold fuel. I assume you're still talking about the om603,

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CENSORED due to not family friendly words

The fuel thermostat is easily rebuildable. The rebuild kit is available from here or the dealer. Only special tool you need is a decent pair of snap ring pliers to remove the snap ring. Once you pull the center piece out then renew the seals and pop it back together. Renew the hoses and you should be good to go next winter.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

It doesn't help starting at all. The idea is to improve fuel atomization while the engine is warming up, for emissions and economy.

Yes 603 and I like the idea of eliminating the thermostat too, but my "dont touch the IP" senses alert to the idea of preheating fuel to engine temp(80C) before the IP. I would imagine the IP gets fairly hot, maybe close to engine temp anyway being nestled next to the block and under the intake, so it may not make a hill of beans(which I think I am trying to do...feel free to say BINGO)....but then why did MB design it to close at 25C-too cool the IP a little bit?

I think I can get what is needed to repair it, but I like the idea of one less place to leak fuel from.

Treetops