WMO burns hotter than diesel?

I'm running a dual-fuel setup in an '81 Merdedes 240D. The temperature on the thermostat is 160-180 running diesel. When I switch to WMO, the temperature jumps to somewhere between 190-200. It always goes up about 20 deg. and it doesn't take its time doing it. You can almost watch it happen. If I switch back to diesel (well, actually 50/50), the temp drops right back down - I mean like you put a garden hose on the radiator.

I am running 50/50 (D2/WMO) in the stock tank. I have a 20 gallon boat fuel tank in the trunk to hold the WMO (100%). I have a lift pump in the trunk and a heat exchanger under the hood. I am using one of those $50.00 eBay eletronic transfer valves (a beautiful thing). The oil I am mainly running came from a buddy who has an elevator shop with work trucks. This is oil-change stuff from the past three years. I can't be sure but, knowing him, there is probably a large amount of synthetic in this mix.

Has anyone else had increased running temps on WMO? Does synthetic cause issues like this?

Think Josh might have a educated answer, but I'll ask some questions just in case.
Does this engine have some sort of cold start advance that thinks the "thicker" wmo is actually colder fuel, then kicks in the advance???
Does the heat exchanger just work on the wmo or both fuels???
Could this wmo have a high content of old gasoline???
Does the idle speed kick up higher when you switch to wmo???
Being the temp rises so quickly, could the temp gauge have a wiring issue??? (meaning its not actually hot but the gauge reads wrong.)
I've run some synthetic oil, not a big percentage, didn't seem to make a difference. But could be....
Sorry about all the questions, just trying to think of things that might make temp rise...

YES... on the WMO part, can't say specifically for synthetic though.

I run my little mail car on almost pure Waste oil most days. Mostly gear oil right now, I'm trying to burn it up during the hot months. Due to some issues with clearance and the hard beating these cars take on a mail rt I have destroyed THREE radiators from hitting unseen potholes, from the radiator fan striking the side of the radiator tank. I subsequently removed the fan cause radiators get expensive quick. I installed an electronic fan controller and use the auxiliary electric cooling fan as the main fan. Because of this, I have to watch my throttle input on parts of my rt.s that have lots of boxes with no distance in between to get any speed for ram air cooling. During these times the little aux fan cannot keep up with the heat being generated by short quick jumps between boxes. The problem becomes LESS of a problem on the days that I have mostly D2 in the tank. I have been running pure D2 in it every 3 or 4 tank fulls to keep the injectors cleaner as my car see lots of idling. Considering that most waste oils carry more BTU's per gallon it only makes sense to see increased run temperatures.

With that said though I will say that I cannot see any difference when I have enough speed for ram air to do the cooling. Anything greater than 35/40MPH in my car. Or in other words if I didn't have a slightly inadequate cooling fan I don't think I would have noticed the difference. SO... that tells me you may have a slight cooling inadequacy as well.

Our little Merzs have radiators designed for highway speeds and only one of the FEW things I see as a shortcoming in the German's designs. If I can find a larger all brass or all aluminum radiator that will fit in the front cap I WILL change it out.

You running a NA or turboed 615? Did they even make a turboed 2.4L? If not then at the 60-70 HP those little 4 bangers output you are working it hard just cruising down the highway. I have read that these radiators were also considered a normal wear part that needed to be changed every 100,000 or so.

My mail car radiator is brand new,(true Merz radiator that was pulled from a car with less than 1500 miles after installing it.) Thanks!! Mr Randy from Exucutive Auto in Blue Spring MO!!! while the little red car's radiator came of of another car with over 200,000. (Yes, I punched my wife's radiator once, and mine twice on a mail rt) My car does not have a proper cooling fan, while little red does. In little red I cannot tell a difference in temps from one fuel to the next.
I'll try and notice if the fan clutch kicks in more on WMO VS D2 the next couple of times little red gets some good juice.

As a guess i say wmo runs hotter but im just assuming this from how a few tractors seem to heat soak a bit hotter with wmo. Ill be getting an egt gauge here in a week or so and when ever i get around to installing it ill be getting some actual numbers instead of guessing that its making more heat. The other thing i wonder is if its slow burn isnt necessarily making higher peak heat as its making heat for longer in the crank rotation.Either way im assuming it will be something noticeable in an egt gauge.

I have had a diesel engine repeatedly overheat during normal running conditions, turned out to be retarded injection timing. I don't know how the Mercedes pump works, but I do know that the bosch style rotary pumps use fuel pressure to advance the injection timing at higher engine speeds, so the fuel supply available to the pump's inlet pipe has to have sufficient flow to ensure correct injection advance. A half blocked filter ( or a thick heavy viscosity fuel) can starve the pump causing air to be sucked into the pump usually through the front shaft's seal, resulting in skewed pump internal pressures, which can affect normal engine operation. How does the merc. pump control injection advance? Maybe you could install a fuel pressure gauge sensing from close to the injection pump fuel inlet, to see if there is sufficient fuel available for the pump.

I never expected so many replies so fast! Let me see if I can remember the questions and address them... This little engine is about as basic as it gets and, yes, it is working as hard as it can just trying not to be a traffic obstruction. The 2.4 never came in a turbo and it is quite possibly THE slowest vehicle on the road. There are school buses that I can't keep up with. Garbage trucks are faster than this thing, but I drive for free.

I'm not sure what is up with the injection timing. I don't believe there is any mechanism to change it for a cold start. This thing doesn't even adjust its own idle. There is a knob on the dash for you to do that yourself. The timing could be off and I have thought of getting into that one day. The cooling system is definitely challenged. Someone ran it for a long time on pure water and what pukes out of it is either green (antifreeze) or brown. But on D2, it always ran pretty cool unless idling in a parking lot. The temp gauge is a mechanical one and, unfortunately, I think it is dead on. It is one of those auto-parts store add-ons and it runs from the heat exchanger. When it says 210, water starts to come out of the overflow tube on the radiator. And the heat exchanger is only for the WMO.

It is possible that there is gasoline in this oil, but definitely MUCH less than if I had mixed 10% RUG. It doesn't even smell like gasoline. Interestingly enough, I had thrown a batch of oil in the D2 tank that came from the engine dyno. Guys would make 2-3 pulls in a brand new engine, then change the oil. That stuff made the car run smoother and COOLER! And, yes, I think my fuel filter is plugged. I plan on changing it today (again). I've been working on my centrifuge and I think it will be up and running today. But, in the mean time, I've just been running filtered oil (down to 1 micron), but I think there is still a lot of sludge left behind,

This car was supposed to be a cheap project for me to get into the diesel game. I've done a LOT with gasoline cars and now I want to get started with diesels. It was a $1,200.00 car that's probably worth $500.00 and I've put another grand into it chasing gremlins not related to WMO. But I think I have most of it sorted out and this car should still pay for itself in a year. I drive 30 miles to work every third day and I was spending $350.00/month on gasoline. Once I get everything sorted out, and some more money saved up, I plan to convert this thing into a nice 1-ton 4x4 extended cab with a manual transmission and a cummins.

Yeah, didn't think they made a turboed 4banger. The 615 or 616 whichever one your car has does not have electronic timing advance. I'm no MB expert, but I think the electronic controls didn't show up on our pumps til the 86 model 603. And although idle speed is electronically controlled, I have not read anything about a cold start advance in even the 603's, but even if it did, it would have to be controlled by the ECM. I'm feeling safe to say that even on the electronic control engines it does not have an automatic advance. All MB pumps all the way up to the late 90's 606 are cam actuated individual delivery valve pumps. Which would insinuate it'd be very difficult to advance them, as the valves and cam are fixed in position. A camshaft drives each cylinders pump individually with the governor in the rear/bottom of the pump. They are extremely robust pumps that have been known to make it into the million mile clubs without anything more than new seals needed.

Retarded injection can bring temps up as someone else stated, our pumps are chain driven, and higher wear engines have often needed a degree or two of advance to take up slack in a worn chain.

Little blue paid for itself in fuel savings a while back, 150-200 bucks a week or more adds up fast. Even better is it actually paid for itself including the repairs I made on it in the very same week it went onto the mail rt if you figured by the amount I get paid on a full week running.

Well, I changed the fuel filter. It may have been plugged a little, but It didn't really seem to make much difference. Last time I changed it, there was a HUGE difference. I also changed the thermostat. It also didn't seem to make much difference. What did make a difference was the sun going down. I know my cooling system needs help. I think the electric fan is a little weak. I'm modifying the front end to accept a large fan from a BMW.

With my marginal cooling system, however, I can definitely say that this car runs hotter on WMO than on D2.

Change the clutch, those are common wear items as well, the silicone or the clutches or both wear with age. If you cannot hear the fan cycling, then it is worn. Wifey's little red has a good clutch, and when it kicks in, it comes in almost instantly, same as an air actuated fan clutch on the big rigs. About 60 bucks last I checked on one.

Yeah, well, I would have done that already but that's one thing that kind of surprised me about this car... it doesn't have one. The fan is bolted directly to the engine with a spacer. And I know someone didn't remove it; I found another one of these in the boneyard and it was the same way. I am finding that, when you bought a 240D with a manual transmission, Mercedes went to great lengths to make sure you didn't get any extras with it. You didn't get a passenger side mirror. They redesigned the front passenger seat so it didn't have the "up and down" adjustment. They put in hand crank windows. And now this fan clutch...

Not unusual, are the blades cast , or sheet steel. Something we used to do on old farm equipment was rebend the blades, it would often help a lot.

Worse. They're plastic. The new bigger fan should help a lot when I get it in. The stock one is so sick, it takes a couple of minutes to even spin up.

Short somewhere making your gauge read higher when you swap over. Too much or not enough resistance

I already said it's mechanical and it appears to be dead on.

Ok then besides engine timing I don't see any other reason