Block Heater Installation Instructions


Please read these instructions completely before attempting this block heater installation.


 Until now, there appeared to be no convenient electric block heater for the Mercedes Benz M180 and M130 engines.  Dip-stick heaters don’t work, lower hose heaters don’t work, external tank heaters add more potential leaks and overcomplicate the already complex cooling system, and there are no freeze plugs to accept simple immersion heating elements.

 While the engine does not have freeze plugs in the standard sense, it does employ “expansion plates” which are much thinner than the engine casting.  Should some coolant freeze, these plates will (hopefully) expand before the block cracks.  There are two plates, located on the right side of the engine block.  One is behind the starter, the other behind the generator.

 The block heater problem is now solved with the “Freeze Plug Heater Adapter Plate.”  It accepts a standard USA- market freeze plug heating element (included,) available at any auto parts store.  It is fabricated from a brand new Mercedes Benz expansion plate, using the TIG welding process.  The adapter plate (with heating element installed)  bolts right to the block in place of the old expansion plate. 

 Either expansion plate location can be used, but the rear (behind the starter) plate is much easier to get to if no other work is being performed.  Logically, if starter or generator maintenance is planned, the time to install the Adapter Plate would be when either accessory is removed.

 THE MOST IMPORTANT THING TO KNOW about the installation is this: BE SURE THAT THE IMMERSION ELEMENT, WHEN INSTALLED, DOES NOT CONTACT ANY INTERNAL ENGINE SURFACE.  If the immersion element contacts an internal surface, it will not work!  When installed in the rear (starter) hole, the element should point forward (internally.)  When installed in the front (generator) hole, the element should point rearward (internally.)

The element is 600W and uses 120VAC.  The heater is located centrally in the engine block, and the heat it generates spreads quickly throughout the entire engine!  For example, at 10°F, the engine, manifolds, carburetor, expansion tank, EVEN THE OIL PAN all feel warm to the touch if the heater is left plugged in throughout the night. Engine temperature can be read on the dash gauge at about 50°C, or over 120°F!  A TEMPERATURE RISE of 80°F to over 100°F can be expected if left plugged in eternally. 

The unit uses 600W whenever it’s plugged in.  There’s no thermostat, so it’s easy to waste electricity with it. Outdoor timers work well for block heater management. In the summer, don’t use it, as it could potentially boil the coolant.

The Freeze Plug Heater Adapter Plate is Wyoming tested and it works very well! 


Parts included in kit:


(1)     Freeze Plug Heater Adapter Plate


(1)      Freeze Plug Heater Adapter Plate gasket


(1)      600W immersion element


(1)   power cord for immersion element

Please note, the immersion element is already installed in the Freeze Plug Heater Adapter Plate.  Do not tighten it any further!


Tools and parts required:


 drain bucket (must hold at least FOUR gallons!)


a 5mm hex-key (Allen) wrench. 


gasket scraper


trouble light


cable ties


silicone sealant (if preferred)

 You would do well to also have a 5mm ball-end Allen wrench.  Also handy would be a ¼”drive ratchet with a 5mm Allen socket.   Don’t use anything bigger as you can easily over torque the six expansion plate mounting screws and possible warp the plate, preventing a good seal.

Some tips:

  1. Allow at least two hours.

  2. This is a prime time to flush your cooling system if it needs it.

  3. Allow your Unimog to cool, as you don’t need to deal with coolant that’s either hot OR under pressure.

  4. If you’re considering removing your starter OR generator for any reason, the block heater installation is SUPER easy with either of these two accessories removed.

  5. Park with the wheels cranked to the LEFT to improve access.

Installation Instructions:

 1.  Park the Unimog on a level surface with the wheels cranked to the left.  As you will be working under the vehicle, set the parking brake, place the transmission in gear, and chock the wheels to prevent an accident.

 DISCONNECT THE BATTERY GROUND, OR TURN THE BATTERY SWITCH OFF (UNDER DRIVER’S SEAT.) You’ll be asking for a short if you don’t, since you’re going to be working around the starter with metal tools.

 2.  Drain the coolant by opening the drain plug at the bottom of the lower radiator hose.  You'll need at least four gallons of capacity in the vessel you’re using to catch the coolant.  A five-gallon bucket works well. (Some engine blocks have a drain between the two expansion plates.  If you have one of these, you do not need to drain from the lower hose.)

3.  On the right side of the block, you will find the two aforementioned expansion plates.  One is just above and behind the generator.  The other is just above the starter motor.  The most accessible (with no other starter/generator repairs planned) is the one above the starter motor.

4.  Open the hood and place a drop light down past the generator so it lights up the side of the block where you're going to be working.  It makes the job much easier to see.

5.  Loosen all six of the Allen hex bolts a little bit, just to make sure you will be able to get the job done.  Once they are all loose, completely remove one of the bottom bolts.  Be sure to have the five gallon bucket ready, because when the first expansion plate bolt is removed the block will continue to drain out through the hole.   Once it's finished draining, remove the full bucket so you don't drop any bolts or tools into the old coolant.

6.  Remove the remaining five hex bolts. Take care to extract the small washers with the bolt as it comes out of the block.  If you drop one down between the starter motor and the block, it's a goner!

7.  Remove the old plate and scrape the face of the opening free of the accumulated crud and old gasket material.  This is important to get a good seal!

8.  Take the new plate, with block heater installed and the new gasket from the package.  Apply sealant to the plate, gasket, or engine block, depending on sealant manufacturer’s directions.

9.  IMPORTANT! When setting the block heater in place, be sure the loop of the heater points toward the center of the block. If you're using the plate above the starter motor, the loop should point forward.  If using the plate behind the generator, the loop should face rearward.  This is to ensure that the element doesn't come into contact with a cylinder inside the block.  If the element touches metal inside the block, it WILL NOT WORK.

10.  Put one hex bolt on the long end of the straight 5mm wrench. Holding the new plate in place with the fingers of your left hand, insert the bolt into whichever hole is most accessible to you and start to thread it in place. Once you get it started you can probably screw it in fairly far with your fingers. Insert a second hex bolt in the same manner. When you get two bolts in place, it will hold the plate steady and allow for insertion of the remaining bolts. Again, take care to not drop one of the small washers.

11.  Snug all the bolts so that even pressure is gradually applied all the way around the plate.  Ideally, tighten them in a radial pattern, as you would tighten lugnuts.  Then go back around and tighten them. 

12.  Attach the power cord to the block heater.  Route the cord to a convenient, accessible location at the front of the Unimog.  Use cable ties to keep the cord away from hot and/or moving parts!  (Should anything ever happen to your cord, NAPA and other auto parts sources carry replacements.)

13.  Put the lower radiator drain plug back in and/or close the block drain.

14.  Pour in two new gallons of anti freeze and continue to fill with fresh water.  (Water : antifreeze ratio depends on your required level of protection.

15.  Start the engine with the cap off of the expansion tank. Watch to see when the thermostat opens, allowing water to circulate and burp any air out of the system.

16.  Add water if necessary, place the cap on the expansion tank.

17.  Enjoy warm and easy starts from now on!

CAUTION!!!  Do not, at any time, for any reason, plug in the heater with no coolant in the engine.  It will quickly burn out, as it requires liquid coolant for heat transfer!