for you 603 guys out there...
 

hello all,
so far i have worked exclusively on the om617 and 616, but i recently bought a 1987 300sdl for a very fair price. its been sitting for a few years and has an exhaust gas into coolant leak (i used a coolant tester and it showed co2 in the coolant)

the issue i have run into is it overheats. as soon as i start it, it heats up and keeps going until i turn it off at 100 degrees. ive used a infrared thermometer to determine that there is significant heat at the top radiator hose, and no heat at the bottom hose. i checked the thermostat and found that there is no thermostat in it currently.

i know about the fan clutch and have determined that it needs to be replaced, but i figure i will get to that after i get the rest of the cooling buttoned up.

next i plan to check that the radiator isnt blocked, then go after the water pump.. anything im missing?

thanks in advance, Jack

The (casting number 14) #14 head in these things is at the delicate end of the spectrum and will blow a head gasket/crack easily if overheated. I wouldn't be surprised if you're dealing with something like that...

Here's a FAQ regarding the #14 head:

http://www.w124performance.com/docs/mb/OM60X/OM603_Head_FAQ.txt

"Very delicate" may be a bit hyperbolic, seeing as countless #14 heads are still on the road 30 years after their manufacture. But your point is still valid.

Having no thermostat installed can cause an overheat. The thermostat both bypasses and cools coolant in varying degrees. As the coolant reaches operating temp, the bypass is closed off little by little and coolant is sent to the radiator. A bit over the operating temp, all of the coolant is sent to the radiator and bypassis closed off completely. With no thermostat, there's no regulation between bypassing and cooling, and the coolant moves too quickly through the system to effectively pick up and reject heat. Old American cars can function without a thermostat, but not these engines.

The #14 casting is a valid point. They're easily ruined if the engine overheats. If you have exhaust gas in the cooling system, you need to remove the head and check it. If it's a #14 and cracked, it's trash. If it's a #14 and not cracked, the head gasket may be the only thing that failed amd you can install the head again or replace it. If you replace it, go with a #18 or newer casting.

thanks for all the input guys, I just ordered a thermostat and i am going to put that in to see if it makes a difference.

another question regarding the head.. my plan for this car is to drive it around until i get the registration taken care of, then take a few days to pull the head and swap in a new head gasket. how bad is it to drive with a gasket leak? if its just gas into the coolant, not in the cylinders or in the oil..

thanks. Jack

Gas in the coolant will cause air pockets in the head, where it can run hot. Heat and hot-spots can be a killer to a head, this one in particular, so I would consider this an increased risk of damaging the head.

Also, high power is high pressure pulses in the cooling system, if you have any question about the condition of the head driving easily is mandatory.

Unfortunatly the head failure is probably more the likely fault than a head gasket. You also indicate that a test indicates exhaust gas in the coolant so a thermostat is not likely to make the car serviceable.

I hope I am wrong though. There are exceptions to what is expected goes without saying.