Coolant question
 

My thermostat is stuck open and I am planning to R&R the thermostat as well as get rid of the green AutoZone coolant which appears to be in my ride right now.

I have most of a gallon of VW G12 coolant (my TDI leaked coolant) that I would like to get rid of. Can I use the G12 in the 617 safely or should I spend the $20 to get some Mercedes coolant? Is filling it back up with more Peak or whatever the green stuff is ok, too? It seems to do an OK job but temps haven't gotten above 90F here yet - with the thermostat stuck open the highest I've seen the temp gauge get is 80C.

BTW, I do plan to drill holes in the new thermostat when I install it. Does anybody here use Redline water wetter? I'm not sure how compatible that stuff would be with G12 or Mercedes coolant.

G12 wont work on a benz. G12 is engineered for VW's and audis. Mercedes coolant is engineered for mercedes engines with the right additivies. Global peak will work too since on the bottle it says meets mercedes specs.

Find some Zerex G-05 at Napa for $10.99 or less. Buy a case........it's going back up to $15. when oil climbs again.

Drilling holes in the 'stat is never advisable. The engine will run cooler when not under full load, but the full load results will be the same. Your only advantage is that the time for the engine to climb in temperature when under heavy load will be increased slightly due to the lower starting point.

If the problems are elsewhere, the solution is to find them.........and it's usually the radiator that is the problem.

I don't know if I have any problems. Just going off the advice of dieselgiant over there. Is his suggestion that the Mercedes cooling system is "barely adequate when running properly" accurate? I don't want to find out that it's true in the middle of a 100F day in Texas.

Just replace the thermostat no holes needed. Just be sure your fan clutch is in good shape, use the "correct" coolant and you should be fine.

Be sure to drain the old coolant out of the block (on pass. side engine). Be careful with the drain on the bottom of the radiator. It is plastic and breaks easily.

Russell has a point about the cooling system. However, we'd need to define "running properly". If we're talking about a new radiator and a clean block, the system is perfectly adequate. If we're talking about a 20 year old radiator that has never been cleaned and a 20 year old block that has never been flushed, then it's a completely different situation.

In any case, the thermostat won't flow any more coolant with holes drilled in the flange. Your only benefit is cooler operation under part load conditions.........it makes you feel a whole lot better........but the engine couldn't care less.

If your radiator is not in excellent condition, you will find out that you've got a problem when it hits 100F. in Texas, and the holes in the thermostat will only delay the inevitable.

Point taken. I guess I will flush, R&R thermostat (OEM, of course) and then fill with the Zerex. If I start to have problems this summer, well, that's why I keep a $900 Honda close to my garage. ;-)

Thanks for the replies.

These are good suggestions...
The MB cooling system is designed differently from most cars...
The amount of junk that can accumulate in the block cooling jacket is amazing... at the rear where the flow slows down stuff falls out... over the years it can affect cooling...
If you are concerned try taking out the core plug holes ( what we see as freeze plugs) and blasting the bottom of the cooling jacket with a power nozzle while vacuuming out at the other hole... then do the other stuff that has been suggested..
In the old days it was standard procedure during a rebuild to take the block to be ' vat cleaned' .... boiled out with some serious hot chemicals...
These days with our long lasting diesel MB's that seldom happens.... having replaceable liners where the pistons can be renewed in place has some disadvantages when it affects owner behavior .....

I don't bother with the drain. I just take the hose clamp off the small reservoir hose and yank it to drain the radiator.

If you want to build a cheap reverse flush kit get some 1/4 galvanized pipe nipples a coupler a 90 degree elbow and about six feet of garden hose. You remove the block drain and screw in a 3 inch pipe nipple. Then screw on the elbow. Then screw on a longer nipple (4 to 6 inches). Take a piece of garden hose and clamp it to the last nipple. Then you can attach this hose to your normal garden hose turn on the water and watch the crap come out the lower radiator hose (which you pull off) I also put a valve on the end of the vertical pipe nipple with an additional 2 inch nipple to attach to the hose. This way I could flush, reattach the radiator hose and then fill the system then close the valve and run the engine for a while. Once the water is fairly clean, I leave the radiator hoses on and flush the whole system with the water coming out of the filler cap. I run the car this way for about 1/2 hour with the mono valve unplugged to get the water through the heater core. If you are changing the T-stat anyway, remove it but leave the gasket and put the cover back on. This way you can flush with the T-stat out as the cold water will prevent the thermostat from opening is it is in place...

I'd just get the proper Benz coolant. It costs less. Save the pink gold for your VW. The pee yellow stuff goes in the Mercedes ;)

-J