94- MB E420- Clogged radiator, bad water pump or thermostat

I would say it is the thermostat. Radiator internally clogged are things of the past. Change the thermostat and see what happens.

Well, changed thermostat and still heating up with center of radiator cold and outsider edges hot.... I think it's a clogged radiator and not water pump... it's backing up at the coolant reservoir when hot... Where can I get a deal on a radiator?

It still might be the water pump not pushing through radiator, but why would it back up at reservoir (maybe cause it's not circulating).... any ideas???? Thanks, MB owner DIY mechanic wanta be....

Forgot to mention car has 170K when I bought it and I'm not sure of last owners maintenance of it... owners book shows oil changes only....I noticed a lot of crud at the outer bottom flange of the heater hose connecting to thermo housing...

Secret to loosening thermostat housing: with bolts removed, bang housing at bolt holes/flange edge (ones you can see) with alternating blows to rotate housing clockwise and counterclockwise, with a wood/ plastic dowel or stick. Six or seven hard blows, back and forth should loosen housing. You'll notice slight shifting of of housing mating to water pump assembly with each blow....patience will save the housing.. FYI

I drained radiator and back flushed it with hot water and could feel heat on fins all around, thusly eliminating a clogged radiator... it all points to a bad water pump cause car runs fine until car opens thermostat, car gets hot, then the top return hose from radiator to water pump is steaming/gurgling and backing up overflow reservoir (water seems to not be flowing). Don't see any leaks by water pump??

Mmm... you done your homework. I am wondering if you have a blown gasket problem... pumping air into your cooling system so that it can never be bled properly.

If you have access to a cooling pressure tester (Autozone loans them for free), make sure you properly release the pressure... then hook up the gauge and pump it up to 15 PSI. See if the pressure stay there. If not, it is leaking somewhere.

Do you have alot of white smoke when you drive?

If you can't find the leak and the pressure keep dropping, then I want you to start the car up with that pressure tester hooked up... keep an eye on it while the car is warming up. Release the pressure before starting the car. The pressure will rise to something like 25 PSI... and then hovers up and down there... but if it above to 30 and keep climbing, release the pressure from the the adapter and shut off engine. This would means blown head gasket.

There is another positive test for head gasket... the CO detector for cooling system.

no... only some on cold days during warm up----60 degrees

Car will run normal temp for about 20 minutes then starts getting hot (below red mark, but never in it, high white line) and when I stop motor I hear a rumbling/gurgling (boiling) sound in hose from water pump to radiator.

I'll check pressure gauge test next...

With engine running, I tried squeezing hose from water pump to radiator and didn't feel any pressure from water pump? I'm hoping it's water pump issue rather than head gasket (ugh!)

Thanks for the help!!!!!

After the car reaches proper temperture, the hose should be stiff.

It may be a strong possibility that your coolant cap is defective... which would cause the bubbling noise as in overheating. Cooling system need pressure to raise the boiling temperature.

Bingo!!!! Cap was defective or maybe a combo of thermostat & cap issues.. car runs at 100 mark and below.... also a trick for a lazy electric cooling fans in front- tap it and if you get it spinning, once at high revs bang it with a rubber mallet, a couple good whacks, it seems to have cleaned the armature or scuffed up the brushes or both...

I weaseled my way out of throwing in the towel with this classic MB that I love... this car is an ultimate driving machine ($54K new back then, I paid less than 10% of original price and it drives about the same, maybe smoother)...much different than the later e's... not as sporty but thoroughbred MB... I owned a 1965 220sb as my first MB that set my standards for MBs... Early posts of mine about rough running after 15 minutes warm up may disappear with cooling system fix....

Thanks! Tiger

.. also a trick for a lazy

Just a note to the above... whack the motor directly at center of front spinning dome in the same direction as the axis of armature...

One good lesson through all of this is: If you can not nail down exact problem, start replacing cheapest item first within system where problem exists.

This is an order to consider for diagnosis:

Check for white exhaust steam Check oil color if milky may be internal leak Check coolant level when hot- be careful of hot/high pressure Check coolant color- should be clear yellow tanish cast not brown or redish (transmission leak) or green(wrong coolant), MB coolant is special mix (or Zerez GO5) Check for leaks- everywhere $6 radiator cap---- just replace $175 ea Electric Fans---B4 you buy- make sure they turn on when hot- if lazy to start after tapping (see prior message for tip to resurrect fan motor) Free Pressure Test--- Autozone test equipment loaner $40 thermostat----B4 you buy--can remove and try the hot water test to open/close it (see prior message for tip removing) $250 Radiator----B4 you buy--try flushing it with hot water and feel heat transmission to see if clogged or remove and take to radiator shop to clean/test it ($80) $375 Water pump---B4 you buy--try all prior steps $400 Fan & clutch---B4 you buy-see how is spins when hot and cool (may not operate well is other system problems)

if you have a bad head gasket it might show up during pressure test (not sure about leak fixes with pour in products.. ugh)

I'm sure there are a couple of other nuggets to check cooling system but also make sure you have good coolant and proper amount bled thoroughly.

Good luck

All good tips... but the most important is where to buy it. I use...