Radiator ,Thermostat,or Water pump ,which to go after
 

The 84 300cd was in need of some radiator fluid service and had been ready to get going on it when I noticed a bit of yeh olde rusty water when drained.I revisited the auto house and returning with some radiator flush ,prestone brand.Drained radiator ,readded clean water with additive and ran as directed with the follow up of the flush ,then repeat .So basically ,in short ,I took a trip and had the system boil at the reservoir at pit stops,the gauge wasnt pegged ,actually set at an acceptable temp.After returning I decided to take out the thermostat and drill 6 holes in the t-stat thinking that would do it.Same result,top small house puffing into reservoir after just 2 minutes of running.I did notice the radiator ,while the engine was stopped ,was cool at the bottom .Next step , give the radiator shop a call for service ,or replace the water pump?

do a citric acid flush .. search it.. then replace the coolant with the proper stuff.. Zerex G-05 or the stuff from the dealership in the grey jugs


do not drill holes in the t-stat... stupid mod


is the fan clutch engaging?

I agree with the Don- citric acid is called for, but if the tubes in your rad are clogged it won't get down there. I wouldn't drill holes in the tstat either on a later car especially.

the holes in the t-stat were more of a test than anything ,just wanted to see were my flow problem originated.Very tough to depress the spring so Ill be ordering another one for install .In the meantime I thought I had successfully completed a cetriC flush with the preston product,Really cleaned out the rusties nicely,Im guessing someone was doing straight water for sometime in the old girl.Im taking the radiator off to exam the tank ,this might be my problem since the heat of the radiator fluid isnt reaching the bottom hose,aka irriatable radiator syndrom.

I don't think there are any commercially available over the counter radiator cleaning products that are worth a cr@p anymore. I think the envronmentalists got to them all. There used to be a good 2-part powder cleaner made by Prestone I think, but that's gone. Citric acid is the best there is now, IMO. You may need to bite the bullet and get a new radiator, or if you are really cheap and frugal like me, attempt to take one of the tanks off and rod the beast out.

I sorta did that with the older 240D. The thing was leaking at the bottom of the tank so I took it off, reamed out the tubes and reassembled it with some extra permatex at the seal. So far so good.

Rick

Are you sure you got all the air out of the system?

I agree not to drill holes in the stat.

Tom W

IF the bottom of the radiator is cold, then doesn't that mean the the radiator is doing it's job? IF the temp gauge was reading ok, and it was boiling over, then I would say either the gauge went bad, or it is ok and you have air bubbles escaping, I am thinking Air in the system also. Or a water pump. My last shot would be a radiator at this point.