high temps 400E cooling problem?

[88260e]

I was in bumper to bumper traffic today and it was our first day over 60 degrees this year and i noticed that the temp gauge shot all the way up to 120 until I put the heat on and it went down to about 100, kept the heat on until I got home??? I'm thinging thermostat ANY SUGESTIONS???

[macdrone]

Blown strip fuse for aux fans against firewall in a tootsie roll sized plastic container. Next is thermostat.

Was your A/C on? Is it charged? if yes then no or non then no you wont get high fan speed on the Aux fans. Which can cause that.

[emerydc8]

If the strip fuse is okay, check the high speed fans by pulling the coolant temp sensor connector off with the engine running and observing the fans go to high.

If they check okay, then check the low speed fans. With the car at idle and the air on, the fans should usually cycle on and off every minute or so, as the coolant temp bounces between approximately past 85-95C (it doesn't sound like yours are doing this). If they don't cycle, check the low speed relay by turning the ignition on and, with a paper clip, jumping the two pig tail connectors that go into the a/c receiver (jump the connectors--not the sensor on the receiver side). If you hear a click when you jump it, the relay works. If the relay works, you could be low on freon. There is also a possibility that the big low speed fan resistor behind the front left headlight is bad, or the terminals/wires are corroded.

[88260e]

I will check tomorrow thanks

[88260e]

Replace thermostat today seem ok, but could not get the aux fans to kick in!!!

[DRICHFL]

Read this from JimF

http://www.k6jrf.com/MB_WW.html

http://www.k6jrf.com/MB_CTS.html

I did this to my E420 years ago and it keeps my engine cool.

[macdrone]

Yes cool harness works but its just a sresistor. But it does just mask issues. After thermostat there will be air in the system make sure you get out all you can. There is a resistor block under the ABS area that can become corroded and make the fans stop working. Also you can jumper the leads on the A/C dryer (with a/c on of course lowest cold setting) and the 2 wire temp sensor on the intake to test for fan operation to force them on. I found when I had to put in my new radiator the fans came on less because it was so efficent compare to the 17 year old one that crack finally and that proper pressure cap kept system cooler and fans almost never come on except at idle stopped at a light with the A/C on as that is what they are supposed to do. The motor temp for them to come on is 105 degrees so unless it gets way up there you shouldnt see them come on at idle (unless you jumper the sensor for proper operation or use cool harness).

[JimF]

Originally Posted by macdrone

Yes cool harness works but its just a sresistor. But it does just mask issues.

A Cool Harness addition turns the Aux Fans (A-F) on at a lower temperature and thus, as DRICHFL wrote, lowers the engine's operating temperature. My many users attest to that. And being "educated" resistor means it it's reliable so it will last a lifetime! NEVER had one fail . . .

It doesn't "mask" issues . . . b/c if the A-Fs don't work, neither will the Cool Harness!

It actually can SAVE you $$$ b/c many VFCs are useless in the older MBs due to leaked silicone fluid. Replacing it provides minimal cooling compared to the cost of a new one. A Cool Harness will easily make up for a dead VFC and it's nowhere near the VFC replacement cost.

Certainly, after a number of years, a radiator that's always seen "tap water" and poor maintenance will produce reduced cooling and eventually raise the engine operating temperature. At some point, it must be replaced. However, a Cool Harness will help forstall its replacement . . . . and it costs a lot less than a new radiator. Kind of like stretching you car's maintenance dollar.

[macdrone]

Yes it does mask issues because why isnt the car cooling correctly that you have to have the fans come on early when the system was not designed to. Thats why anytime you turn on A/C they come on and from 105-110 they come on because the viscous fan and normal driving it should never get that hot overall. That is an issue if it does. The resistor masks the problem.

problem 1 is usually thermnostat staying open too long letting system throughout get hot.

problem 2 is viscous fan not staying engaged at high heat because its leaked out all its internal oil

problem 3 is low freon charge (normally due to evap leak) or a bad sensor on the dryer, or the ballast on the fenerwell that supplies power to the electric fans.

problem 4 can be the water pump.

problem 5 reservoir cap has a leak which allows boiling in the system.

problem 6 is scale buildup in the radiator tubes not allowing proper cooling, also bent fins, leaves whatever the case may be.

I hope you find the issue but it is an issue if you let it go if its getting close to 120(redline).

I replaced most of my stuff over 3 years and now with everything cleaned, new and working I never go past 100 with A/C on full blast stopped or driving. I normally set at 85 all the time with A/C on cool days just under 90 on hot days driving to Spokane, Wa when its hot.

[88260e]

Car got real hot in traffic today so when threw the car again an, wanted to kick myself!!!! relays were good fuses were good strip fuse "LOOKED" good until I touched it AHHH HAAA it was split and I missed it the first time I checked!!!!!! hair line crack right in the middle time to track one down, are they a dealer item???

[macdrone]

No , but a better replacement is the blade fuse socket (in line fuse) that you can screw down to the screws to be able to buy a fuse you can buy anywhere. The strip fuse is dealer part normally but any place that sells MB parts online will have them.

[88260e]

Installed the inline blade fuse today, did the trick!!!!!!!! Thanks for for the help!!!!!!

[macdrone]

Ya that strip fuse sucks, I still use the stock strip fuse buyt im silly like that.

[88260e]

still problems DAMN!!!!!!!!!!! fans don't seem to kick on by themself!!! Could it be the coolent temp sensor??????????

[macdrone]

Yes as there not supposed to come on until 105-110. But why is it getting so hot in the first place? I would suggest going through my earlier suggestions.