My 300TE is overheating.

New radiator...Behr.

New thermostat...also Behr.

Zerex ZO5, 50/50 mixture.

New hoses, clamps.

Car starts and runs well. If on the Interstate temp stays at about 90* until we get off the freeway and on to stop and go traffic. Then she starts heatin'.

Off with the A/C...turn on the heater...down she comes a bit. Both fans are on any time she goes over 100*.

229,000 1991 300TE

Water pump changed at about 150,000 at the MB dealer in Phoenix.

Checked all the threads, there doesn't seem to be a water pump test...or am I living it?

Thanks for your inputs...in advance.

Check to be sure the cap holds the specified pressure. This is an easy test. Just take the cap in to an auto parts store. They should have a pressure testing device that you attach the cap and pump up the pressure. It really could be as simple as a new cap!

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Charles
1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale: http://www.peachparts.com/shopforum/showthread.php?t=296386

Please be more specific. What is happening? The temp gauge reads high, or is steam coming out or what?

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

What's the condition of the fan clutch?

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120 is overheating, is it making it to 120 with both fans on at 100 degrees? Pressure test the system? Any pressure loss will let the coolant boil and start to overheat. With youre new parts its most likely not your water pump, maybe the thermostat they go bad alot even when new.

I am drawn to say your electric fan and vicous fans are not doing there job if they both run and it still gets hot, unless like i said you have a pressure leak somewhere.

Sounds to me like the coolant is just low. Check it again even if you are sure.

Check the fan clutch by spinning it when car is stone cold. If it turns more than 1/3 turn by spinning it, it is dead.

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nestorb98, trust you installed an 87 degree C thermostat. As mentioned, sometimes new ones are faulty right out of the box. Try a Wahler 87 degree C thermostat, and be sure the vent hole is towards the firewall (at least that's what I recall as the correct orientation). Also, confirm the coolant expansion tank cap holds the proper pressure.

While you have the thermostat removed verify the coolant level is just below the thermostat housing flange. If not, add coolant mix before installing the thermostat.

When filling the radiator I use a short piece of clear hose temporarily attached to the upper radiator connection to ensure the radiator is completely full. Then remove the clear hose and install the upper radiator hose.

Until the problem is resolved check the coolant level in the expansion tank when the engine is cold. Add coolant mix as necessary. It's possible there is a pocket of air trapped in the cooling system.

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Fred Hoelzle

Get a 79c thermostat and cool harness. Ditch the clutch fan. It's a worthless paperweight.

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CENSORED due to not family friendly words

There are absolutely NO leaks anywhere. Temp will stay pegged at 90ish if I'm driving on the freeway. It's only when I get to bumper to bumper that the temp goes ballistic. Then it red lines and I stop and allow the cooling fans to suck the heat out. I do this by shutting the engine off and turning the key to the start position. I also turn on the heater to full.

No steam.

Drives just fine!

AAAAAAAARRRRRGGGHHH!

thanks for reading!

I have to say it's in good shape.

I know this because I have a 95 E320 wagon and it works fine and the fan clutches on both feel the same. I tried spinning them, the newspaper test, they are both identical in operation.

thanks.

Suspect cap and/or coolant level. Maybe a blockage up there? Paper? Bugs?

I had my 300sel out yesterday and it was in the low/mid 100F area in Texas yesterday and my temps were okay. Obviously the A/C was on. Mind you I do run a 79°C stat.

Temps stayed in the mid 80-90°C, according to the in dash gauge.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

thermostat, cap on reservoir or crack in reservoir. I had to replace all of it due to hairline cracks. If the radiator had to be replaced bet your bottom dollar that plastic tank is toast and not holding pressure. If its not that id say your head gasket, thermostat or radiator are garbage. If you stay cool at speed the water pump would do enough at idle.

How can it be losing pressure through hairline cracks if the coolant level doesn't change?

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You cant check level when hot, must be checked when cold. Do not over fill reservoir. Im pretty sure he is losing something as you have to because the pressure cap would let fluid out at 120 degrees. Again there is a piece missing because maybe too close to the problem. At 120 the water being full/hot(expanded) would allow opening of the cap and siphoning back and fourth into the overflow in the fender. The reservoir is actually and expansion tank. The hose from it goes into the passenger fenderwell where it has the overflow tank.

Again a piece of the puzzle is missing. The system seems complicated but its not really. Fairly easy and straight forward.

Coolant is in the system held at atmosperic pressure from the cap, pumped by the water pump through the engine, as it reaches thermostat temp that open and allows water into the radiator, it cools it 15 degrees in its process and already cooled water goes into the block to circulate. Thats it for the coolant. For the radiator to do it job it has 3 ways. Aux fans/fan, vicous fan, and air passing while moving. The aux fan will come on if/when a/c is turned on with acceptable freon pressure, or the temp sensor for the fan reaches 105. If he says the viscous fan is good and his fan/fans operate full time after 105 then his radiator is bad, thermostat, or a pressure leak because if the water pump was bad he wouldnt cool off while moving because water would not circulate at all. A thermostat stuck shut or open will cause his issue, or a pressure leak allowing the water to get hot and boil. The radiator could be full of scale if its a few years old and he didnt fill it with distilled water, but I doubt it. He replaced the radiator that was bad but the expansion tank is plastic also why didnt it get replaced? it was now the weakest and most sensible thing to go out. Mine leaked for a long time before i noticed a white line along the edge that was dried scale from a leak that seamed small but when it got hot it sprayed while driving at temp and rpms, then at idle it wouldnt do it. When I would shut the car off the fluid would appear full, because the overflow would suck fluid back it from the cooling off.


Your results may vary but im just saying.

Dont forget to check your transmission fluid level also, too low could add extra heat from the transmission cooler lines.

Thank you all for your combined inputs.

Today I "burped" the cooling system fluids, exchanged the coolant cap with my 95 and topped off reservoir.

Drove to work and the temp stayed just under 100* and never reached the previous day's high. Ambient temp was around 105* (this is Arizona).

I am extremely relieved to see that it is not the water pump. The cost and knuckle scrapes would have been hellish in these temperatures.

So "burping" is the key.

I never would have thought of it on my own...thanks again all, for your assistance.

best regards,

nestorb98