Author Topic: Temp guage  (Read 1955 times)

1974450SEL

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Temp guage
« on: 10 July 2009, 07:08 AM »
What does everyone's temp guage read on their cars while driving on a hot day with the A/C going?  On a cooler day mine reads a steady 175 (dead center on the guage) but with A/C running it jumps to about 185-190 just below the 200 mark (3/4 way on the guage) but never to the max of 250.  Does this sound about normal?  Also does anyone have issues with their idle going down to almost nothing after they've driven for a bit?  I've corrected this but adjusting the screw and hope it stays fixed. 

TJ 450

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Re: Temp guage
« Reply #1 on: 10 July 2009, 07:19 AM »
Hi 1974450SEL,

175 is about where it should be, maybe creeping up slightly when idling in traffic.
Anything much higher than that is suggesting that there may be a problem with the cooling system. BTW, what would the ambient temperature be when this is occuring?

The electric auxiliary fan should also be running when the A/C is on.

The idle dropping off to nothing suggests that your auxilliary air valve is not functioning correctly, meaning that it requires a greater temperature than it should to fully close.

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

1974450SEL

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Re: Temp guage
« Reply #2 on: 10 July 2009, 07:29 AM »
Hello Tim,
   85-95 F.  I've suspected the Aux valve since I bought the car 3 years ago.  It used to do this erratic  surging during the winter time till it warmed up.  I will have to either fix or replace that at some point.  I'll check the A/C fan operation.  I also have a new thermostat I may install.  Radiator does not leak a drop and the regular fan and clutch appear operational. 

1974450SEL

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Re: Temp guage
« Reply #3 on: 13 July 2009, 06:21 PM »
Changed the thermostat, flushed system, put in new coolant over the weekend.  Today I disconnected the aux fan and ran it straight to the battery to test operation and it works very well.  I cleaned out the part where it connects and checked the fuse box to see if any fuses were blown and they were all good.  Not sure why this fan is still not coming on when the A/C kicks on.  Any suggestions?

TJ 450

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Re: Temp guage
« Reply #4 on: 13 July 2009, 07:10 PM »
If you look on the receiver dryer next to the fan, there should be two refrigerant switches. One of them should control the aux fan... I think it's the lower one. You can check to see if there's an electrical fault outside the switch by shorting the two connectors with the engine running. From memory, I think it should engage the compressor clutch as well as start the aux fan. If it doesn't engage the fan, there may be a problem with the switch, or the fan is wired differently.

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

koan

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Re: Temp guage
« Reply #5 on: 14 July 2009, 12:21 AM »
Not sure why this fan is still not coming on when the A/C kicks on.  Any suggestions?

It comes on if the refrigerant temperature gets too high, not when the compressor runs.

Also comes on when coolant gets to 100C.

koan
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1974450SEL

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Re: Temp guage
« Reply #6 on: 14 July 2009, 07:47 AM »
Koan,
  Yea I saw that in an older post regarding these aux fans.  100 C seems a bit to warm for the engine to be running, do these older MB's run hotter than newer ones?  Would it hurt anything to wire this to come on when the compressor is on?   
  Tim I'll try yours trick as well. 
  I'll be taking a trip up to New England and don't want it to overheat next month, so I am doing alot of P.M. on the car. 

pez

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Re: Temp guage
« Reply #7 on: 14 July 2009, 09:17 AM »
Koan is exactly correct regarding the function of that switch on the drier.

It's worth checking it to be sure it will cause the fan to turn on.

I agree, 100C is a quite high. I personally wired a switch into my dash that creates a ground connection to the aux fan. This means that all the functionality that MB built in is still there [it will turn on at 100C and/or if the refrigerant temp gets too high], but additionally, I can turn it on too.

On a really hot day, I will run the aux fan when I am in traffic below about 45mph.  I find that it makes a difference not in coolant temp, but in how cold the a/c blows.

On the hottest days, in traffic, I might see 90C at most.  Generally, 85C is normal for my 76 450se euro.
1976 450se Euro Daily Driver....currently 4 sale, moving to Mexico

1974450SEL

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Re: Temp guage
« Reply #8 on: 16 July 2009, 04:01 PM »
Pez, how exactly did you run a ground wire?  I'd like the option of being able to turn it on and off.  For now, I have a new temp switch on order because the fan does not come on when the temp hits 100C. www.Rockauto.com had some close out prices on stuff and the switch was $6.00 American.  They are a good site for parts here stateside. 

pez

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Re: Temp guage
« Reply #9 on: 16 July 2009, 05:16 PM »
I put a T in line with the aux fan temp sensor....that way the sensor will turn it on, or me throwing a switch [simple toggle, which I mounted on the knee panel below the ignition switch] will also turn it on.

The wire is then run to the top engine mounting bolt for the alternator [a good strong ground point].

If you need photos, let me know and I'll see what I can do for you.

All together, it took about 10 minutes under the hood and about 30 minutes under the dash to install and wire the switch.
1976 450se Euro Daily Driver....currently 4 sale, moving to Mexico

1974450SEL

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Re: Temp guage
« Reply #10 on: 17 July 2009, 06:37 AM »
Yea photos would be great!  If you don't want to post here send to my inbox on this site, whatever is easier!