I have an electric fan on the stock rad of my 1953 Mercury M100 (same as F100 bascially) and need a temperature switch.
Can anyone tell me the pro's & con's of mounting the switch in the rad reservoir over mounting off the engine block?

The driveline is 5.0L/AOD Fuel injected from an '86 Lincoln Mk. VII.

If I put it in the rad...I'm using a recored stock rad, so should I place the temp switch in the top or the bottom where the initial tranny cooler is?
Does it matter or should I just go for ease, cost and looks?

Also: I pulled the rad after thinking I'd sprung a leak, only to find out that it was simply overflow going out the overflow pipe!!! Am I better to change the cap or put a reservoir to control the overflow?

Appreciate your input.

53Merc

 

Put it in the top part of the rad. As the water enters into the top part. I have two units with electric fans. The flexi-lite kit comes with a tube you place in the upper tank or upper rad hose. The spal kit uses a sending unit you screw into the intake manifold by the thermo housing. The flexi-lite has a adjustable on/off switch so you can set when you want it to come on. Ie: 200 f etc..

 

Also go with the reservoir tank, either a cheapie plastic aftermarket one or a nice polished stainless one, don't matter. A lot of engines run fine but will push out a little water, especially within a minute or so after being turned off. However, using the right cap, it will allow the radiator to pull that water back in from the reservoir as it cools down. You won't have to add antifreeze before you leave each day because it "looks a little low", only to have it push it out later in the day.

 

Put the heat sensor in the most convenient place to keep it from being damaged. Then set the start temp for the fan at the lowest possible temp. That way the fan comes on as soon as you turn on the ignition switch. This serves as a check to make sure the fan is working before you even start the engine. Otherwise, you are in trouble two miles down the road when the radiator starts to gush.

Scott: Sorry, but I do not agree that the coolant is somehow sucked back into the radiator. Since the radiator runs at a positive pressure of 6 to 15 pounds depending on which engine you have, there is no way for the cap to open and let any fluid back in. Also, the cap is spring loaded to keep the cap sealed unless pressure overrides the spring strength and allows fluid to escape. I know that most people reading this probably think that I am crazy because we have been told for years that fluid does go back into the radiator. However, I don't think so. That is why I check the fluid level in the radiator not the overflow container. John

 

The stock radiator is a low pressure unit. If you put the 16 lbs cap on it, it will split the seams.

A high pressure radiator is still made.

I put my temp sensor bulb in a blind 3/8" tube about 12" long that I had soldered into the top tank.

 

Scott: Sorry, but I do not agree that the coolant is somehow sucked back into the radiator. Since the radiator runs at a positive pressure of 6 to 15 pounds depending on which engine you have, there is no way for the cap to open and let any fluid back in. Also, the cap is spring loaded to keep the cap sealed unless pressure overrides the spring strength and allows fluid to escape. I know that most people reading this probably think that I am crazy because we have been told for years that fluid does go back into the radiator. However, I don't think so. That is why I check the fluid level in the radiator not the overflow container. John [/B][/QUOTE]

John, the coolant definitely is drawn back into the radiator from the overflow container. I had a 29 Ford with a Walker radiator and used one of those inexpensive aftermarket plastic overflow containers. I could never fill it more than 1/4 full because when the car sat after running, it would push the level to 3/4 full. If I filled it more than 1/4 full it would overflow when I shut the engine down. Think about it, if you always added coolant to the radiator and it kept pushing it out to the overflow, eventually the overflow container would run over. Have you ever noticed that in most owner's manuals of newer cars they always tell you to add coolant to the overflow container and not the radiator?

 

Yea Vern I have noticed that they say that in the new manuals. However, I have also seen several trucks in our fleet that were low on fluid in the radiator but had plenty in the overflow tank. I agree that fluid can come out of the radiator into the tank. If pressure builds up too high, it overpowers the tension of the spring in the cap. It then runs down the small hole on the side of the filler neck. The part that troubles me is that the manufacturers want us to believe that at some point the radiator creats a negative pressure (less than atmospheric) and the cap spring then opens allowing this "vacuum" to draw the fluid out of the overflow tank and back into the rad. (When the radiator cools?) Why doesn't outside air satisfy this vacuum by interring in through the space between the cap and the filler neck? It just seems like too much faith and not enough physics to convince me. I guess we'll just have to agree to disagree. Thanks, John

 

Vern, I'm thinking along your lines. I had to go check my radiator caps last night just to be sure I hadn't dreamed it up. On my 65 mustang and 99 explorer, when you take the radiator cap off and turn it over, there's the little brass middle part that is against the seal. It is held shut with a weak spring, and you can pull it out a quarter inch or so. I believe when the engine is running hot like on a summer day, and is shut off, it will push out a little water just from heat and expansion, but as it cools, this "plunger" is pulled out and allows the radiator to draw the fluid back in. Besides, that's why the recovery tanks have "full when hot" and "full when cold" levels written on them.

But anyway, let's not forget the other reason for putting on a recovery tank. My wife's a cat lover, and I have to admit I like the little brats too, but cats, dogs and other little creatures like the taste of antifreeze, which will kill them in a pretty painful way. If anything, put on a recovery tank to keep from leaving little toxic puddles of antifreeze in your driveway.

Scott

 

Excellent Guys!
I've been away for the week but this is the kind of discussion I was looking for. Thanks Why is no one suggesting the block for the sensor...I thought it would get hotter sooner and turn the relay to the switch on sooner?

LMK

and thanks again for good input!

'53Merc

 

One off our present vehicles has a recovery tank with 'Hot" and 'Cold' levels marked on the overflow tank. That makes it convenient to 'top off' the rad. at anytime.

 

53Merc,

I'm putting a 5.0, T5 in my 55 and will definitely be going with an electric fan. At this point, I intend to put the temp sensor in the bottom or return tank as is done in a lot of European vehicles including Audi and VW. Here's the reasoning. The rad's job is to take the heat out of the coolant. If the coolant returning to the engine is below a certain temperature ( I beleive the VW sensor is about 180 ) there is no need for the fan to come on. As air flow is restricted because of slower driving or idling in traffic, the rad can't reject sufficient heat, The coolant coming out of the rad hasn't been cooled down enough and the fan needs to come on to pull the air through. The temp of the lower tank would be a very good indicator of this condition. What I would like to do, is go with a 2 speed fan and a 2 level switch as VW and Audi do it, but I'd like to do it with Ford stuff and I believe that Ford uses the thermostat housing temp to switch. I have seen switches that mount into the drain petcock opening so you just undo the temp sensor when you want to drain the rad but the only ones that I have seen are single temp switches.

 

Why is it necessary to have such a complicated setup? Why not have the fan run continually? The thermostat in the engine will modulate the flow of coolant to keep the operating temp steady. Good luck, John

 

This is a little off topic but last year we filled our 500 gallon water tank from our well. We just shut off the tap and left the hose in the tank. The next day half the tank had been sucked back in to the well.

 

I would agree that runing the fan continuously would be easier, and the engine thermostat would certainly modulate. But, I guess I like to complicate and all modern vehicles with electric fans have thermostatic control. For me its a question of not running tte fan when its not needed which is certainly the case when cruising down the highway. Reduces wear and tear and the fan motor as well.

 

To each, their own. For me the security of turning on the ignition and hearing that fan come on is great. Good luck, John