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  #1  
Old 07-18-2010, 05:50 PM
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Electric fan on 280SE 4.5

I have a '73 280SE 4.5.

When is the electric fan mounted in front on the radiator supposed to come on?

I was driving the Red Baron yesterday in 100 degree heat, and at idle with the a/c on, the temp gauge would start to climb close to the red.

When I got home, I let it idle in the garage to see how high the temp would get, and it got right up to the red mark and stop, which is clearly too high.

I notice the electric fan never came on, and it got me to thinking that it should come on when the a/c was on or when the temp got to a certain temp.

In any event, neither the a/c on or the high temp triggered the fan.

FWIW, the radiator is newly recored.

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2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".
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  #2  
Old 07-18-2010, 09:37 PM
D&W D&W is offline
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cant offer any help but my 68 280se inline 6 has been climbing with the increased heat lately.

apparently it is common to have cooling issues.

I too will watch the responses.

It has been recommended to me to keep an eye on coolant, possible install an electric fan (mine doesnt have one) and possible re-core.

for the time being careful driving and monitoring can keep it under control. keeping the a/c switched off certainly helps
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  #3  
Old 07-18-2010, 09:55 PM
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Your 4.5 should NEVER get to the red. If it gets halfway between 212 and the redzone, I'd shut it off. Pretty sure that's how my old cams got fried (literally). Your fan clutch may not be working. Your radiator probably is scaled to kingdom-come. Your block almost surely has a ton of crud blocking coolant flow. Your water pump fins may be gunked closed or corroded off. Whatever the case is, service that system!!

The fan should come on any time the A/C is on regardless of engine temp, and any time the engine hits 212F or more. There's a water temp sensor with a 1-prong plug to the right of the air intake mount, as facing the engine. Short this on the (-) (anywhere on the body will do) - if the fan doesn't come on, either your fan fuse is corroded or blown, the relay's shot, or the fan is bad. If it does, this sensor is shot.
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Electric fan on 280SE 4.5-212-sensor.jpg  
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  #4  
Old 07-18-2010, 11:14 PM
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As TomGuy mention, you should be able to jump the fan and have it run all of the time while the engine is running by grounding the plug to the 212 switch or joining the connections that go to the pressure switch on the dryer.

It should be fine to have the fan running all of the time during the summer.
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  #5  
Old 07-18-2010, 11:16 PM
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Quote:
Originally Posted by Tomguy View Post
Your 4.5 should NEVER get to the red. If it gets halfway between 212 and the redzone, I'd shut it off. Pretty sure that's how my old cams got fried (literally). Your fan clutch may not be working. Your radiator probably is scaled to kingdom-come. Your block almost surely has a ton of crud blocking coolant flow. Your water pump fins may be gunked closed or corroded off. Whatever the case is, service that system!!

The fan should come on any time the A/C is on regardless of engine temp, and any time the engine hits 212F or more. There's a water temp sensor with a 1-prong plug to the right of the air intake mount, as facing the engine. Short this on the (-) (anywhere on the body will do) - if the fan doesn't come on, either your fan fuse is corroded or blown, the relay's shot, or the fan is bad. If it does, this sensor is shot.
I think the fan clutch is working. I opened the hood and watched it spin.

The radiator was just recored.

The previous owner had a problem with the fan not running, so he re-wired the fan to run whenever the key was on.

I had my mechanic rewire it back to the factor setting.

The fan didn't come on when the a/c was on nor when the temp got past 212.

Does this mean I have a bad fuse?
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2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".
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  #6  
Old 07-18-2010, 11:26 PM
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You might have a bad fan relay. Tap the metal can relays while you have the over heat sensor (not the temp sensor) grounded. Pretty common for those old mechanical relays to stick. You can pull them apart and clean them or replace them (my recommendation) with a newer plastic case Bosch relay. You have to do a little re-wiring of the ends but it's well worth it. I mean, it's all nice and well to have your car original but to have your car original with the pistons melted to the cylinder walls is not all that keen.
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  #7  
Old 07-18-2010, 11:39 PM
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Quote:
Originally Posted by D&W View Post
apparently it is common to have cooling issues.
It is not common to have cooling issues. If the car overheats, look for the root cause, bad thermostat, scale in the cooling system, bad radiator cap and bad fan clutch.

Get the service manual CD's and it will detail when the fan will turn on. You can always made some modifications to turn the fan on over a certain temperature depending on driving conditions.

Don't forget, these cars are high speed cruisers.
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Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

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  #8  
Old 07-19-2010, 01:15 AM
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Its normal for them to warm up a bit at idle, no more than 212F(100C) though.

How old is the thermosat. I just put a thermostat in a 73 450SL and the old original unit came out in pieces, it corroded so badly it was stuck to the block.

Touch the 2 wires that go to the aux fan switch on the AC drier together, the fan should turn on. If it does then you need to replace the switch on the AC drier, and the 212F switch on the motor is self.

It also never hurts to replace the sensor for the gauge on the dash, over time they being to give out false readings.
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1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

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1976 300D 195,300 miles
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  #9  
Old 07-19-2010, 10:13 AM
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Quote:
Originally Posted by 79Mercy View Post

How old is the thermosat. I just put a thermostat in a 73 450SL and the old original unit came out in pieces, it corroded so badly it was stuck to the block.
One thing to check, is that the car has the proper thermostat and that it is installed properly. The earlier cars used one with a lower temperature (75C) while on later V-8s, I think this was increased to 80C.

BTW - When cars are converted to R134a, it is recommended by some, that the electric fan be wired to come on whenever the A/C is on.

If car is overheating, it may be worthwhile checking the timing. It may be retarded or the centrifugal advance may be stuck. (I would forget the factory specs and set it so it is so it is close to 30 deg BTDC at 3000rpm with no vacuum.)
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  #10  
Old 07-19-2010, 02:09 PM
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Tangential question if I may - we're about to get the radiator re-cored on our 72 280SE 4.5 (have been planing too, events have conspired to make it suddenly necessary to do it now as in pull the radiator as soon as I get home tonight ).

Scale of 1-10, with 1 being pulling the radiator out of my miata (~ 4 bolts, top & bottom hose, wiggle and pull and yer done in half an hour) and 10 being the 74 AMC Matador radiator I got stuck pulling (grill, brightwork, loosen suspension mounts, hoses + trans cooler lines, etc etc etc taking 8 hours+): where should I expect the Gustav's radiator removal to fall?

He's an automatic, so I know I'll have a couple tranny lines not found in my yada ..... will I have to pull the fan? Anything else have to come off before the rad comes out?

Obviously I could figger this out myself if I were home, but I'm not, and trying to get an idea what I'm getting into tonight....
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1961 220b: first project car - sold.
2000 CLK 430: first modern Benz - sold.
2001 CLK 55: OMG the torque!!! - sold
1972 280SE 4.5: Baby Gustav
1991 300TE 4Matic: Gretel the Snow Bunny - sold
1978 300SD: Katz the Free Man - given away
1980 Redhead: Darling Wife
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  #11  
Old 07-19-2010, 04:15 PM
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Remove 4 fan shroud bolts.
Drain oil cooler.
Remove upper & lower oil hoses.
Remove transmission cooler lines.
Drain radiator.
Remove upper & lower coolant hoses.
Remove 2 "Rubber bands" if still intact.
Lift out radiator (may need a jack if stuck, with a 2x4 longways underneath to prevent damage to the radiator).
I'd rate it about a 3 in difficulty on a 1-10 scale. My Jeep is more difficult, probably a 5, & it's just the radiator that would come out (trans cooler is not attached to the rad, no oil cooler).
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  #12  
Old 07-19-2010, 05:13 PM
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Excellent! Thanks Tom.
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1961 220b: first project car - sold.
2000 CLK 430: first modern Benz - sold.
2001 CLK 55: OMG the torque!!! - sold
1972 280SE 4.5: Baby Gustav
1991 300TE 4Matic: Gretel the Snow Bunny - sold
1978 300SD: Katz the Free Man - given away
1980 Redhead: Darling Wife
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  #13  
Old 07-19-2010, 10:44 PM
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Radiator is out, thanks to Darling Wife. I stood around and handed her tools and and maybe twice added advice.

She wants to know how to do everything. Damn good student she is.

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1961 220b: first project car - sold.
2000 CLK 430: first modern Benz - sold.
2001 CLK 55: OMG the torque!!! - sold
1972 280SE 4.5: Baby Gustav
1991 300TE 4Matic: Gretel the Snow Bunny - sold
1978 300SD: Katz the Free Man - given away
1980 Redhead: Darling Wife
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  #14  
Old 07-19-2010, 11:10 PM
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Well done!
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Al
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  #15  
Old 07-20-2010, 05:29 PM
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Quote:
Originally Posted by ramonajim View Post
Radiator is out, thanks to Darling Wife. I stood around and handed her tools and and maybe twice added advice.

She wants to know how to do everything. Damn good student she is.

You look like a twig man, eat some food! Oh, wait...

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1999 Chrysler 300M - RIP @ 221k
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