Found an interesting thread on OM606 fuel supply on another forum

[Diseasel300]

Originally Posted by Maxbumpo

I don't agree, heating the fuel in the tank will help to drive out any water in suspension (if any). Water in the bottom of the tank is where the fungus lives, so anything that minimizes water is a good thing.

All the 201 and 124 diesel engines incorporated the fuel heater / thermostat in the mid 80's, so it has been around for a long time. Most cars won't suffer at all if this system is bypassed, but I'm not in favor of taking the risk with my cars.

Have you bypassed the fuel heater on any of your cars? It's bypassed on mine and I can assure you that the fuel returning to the tank once the engine has reached operating temperature is quite warm. The fuel heater may speed up the heating of the fuel, but the IP will do it's own job heating the fuel, remember it's full of engine oil at the same temperature as the block.

The fuel heater won't help with fuel gelling, it doesn't work until the engine block is up to temp, and it has components that are frequent failure items. Nobody else uses fuel heaters, prior to the 60x engines, Mercedes didn't either.

On my fuel heater thermostat, the wax pellet in the thermostat element failed and cause full heat full time. I discovered it during a Diesel Purge when the polypropylene bottle I was using started melting and the Diesel Purge was steaming out of the container. I didn't, and won't be rebuilding my thermostat, it is bypassed permanently.

[Maxbumpo]

Originally Posted by Diseasel300

Have you bypassed the fuel heater on any of your cars? It's bypassed on mine and I can assure you that the fuel returning to the tank once the engine has reached operating temperature is quite warm.

No, both of my diesels still have all that in place and operating.

That's interesting that your fuel return is still nice and hot. I wonder what the difference in temperature there is between my car and yours?

[97 SL320]

Originally Posted by Maxbumpo

I don't agree, heating the fuel in the tank will help to drive out any water in suspension (if any). Water in the bottom of the tank is where the fungus lives, so anything that minimizes water is a good thing.

Unless the fuel gets near 212 F , water will be very slow in evaporating. Also, any evaporated water needs to go somewhere however the tank vent is pretty small compared to tank volume.

I'd tend to think that heating fuel would tend to make bugs grow better.

Somewhere in a service manual , new product info manual there has to be a description of this heater and why it is used.

Originally Posted by Diseasel300

The fuel heater won't help with fuel gelling, it doesn't work until the engine block is up to temp, and it has components that are frequent failure items. Nobody else uses fuel heaters, prior to the 60x engines, Mercedes didn't either.

Engine coolant starts building heat reasonably rapidly and would be able to get above the 10 to 15 *F gel and 32F* cloud points. However, fuel filters / strainers are the typical points where fuel gels so heating fuel won't help a engine that has just been started, you need an electric heater on the filter for that.