MG Sports Cars

My radiator fan switch just failed (Dodge Caravan style screwed into top of radiator). SInce this switch really didn't fit well (hit hood without modifications), I'm considering going to a style that mounts between fins through the radiator (like Hayden 3652). I also understand there is a style that mounts in radiator hose, but haven';t seen that on internet. Suggestions?

Hi Don,

There are tons of opinions on fanswitch placement.
In my experience the top of the rad is a poor spot for two reasons.
One. Any drop in coolant level renders the switch useless and Two. the switch is in the wrong spot to measure the operation of the rad. It's measuring hot water coming in. It has no idea if the rad has cooled the water that is leaving or not.
Rad fin sensors are not very accurate as they don't have any direct contact with the coolant and mounting options affect the readings greatly.
For me the best spot tends to be the bottom or outlet of the rad. This gives the sensor a true reading of the rads performance and whether or not the fan needs to be on.
I usually use a VW two speed fan switch mounted on a bung soldered to the bottom of the rad. (any rad shop can do this easily). Or have a tube and bung assy made up to fit in the lower rad hose. Works just as well just not as pretty looking.
The VW switch gives me two temp on options. Or better, lets me wire the fan(s) for high and low speeds.
Use a relay(s) to operate the fan(s) and your switch will probably outlast the car.
Lastly I tend to wire the fan up with constant power so it cools when the car is off. This helps heat soak problems. Just make sure to put in a service switch so that you can turn it off when needed.
Hope thats usefull.

Cheers
Fred

I used this from sumitracing with a sensor turning on my fan @ 205 and turning off at 180. It seems to work well so far.

Calvin - Do you have a supplier/part# from Summit? Looks perfect!

Fred knows more than I do about such things so I would probably follow hs recommendations. I don’t profess to know how accurate it is, but mine screws into the intake manifold and comes from Speedway (link below) I think it about $15.99 but they recommend a relay which is also rather inexpensive. They come in both 3/8" and 1/2" NPT.

"P"



[www.speedwaymotors.com]

I use a Flex-a-Lite adjustable temp control #31147 to control the fan on my 60hp (pic #1). I installed the controller inside an old regulator that wasn't needed as I'm using an alternator (pic #2). The sensor is inside the top radiator hose (pic #3). Marvin

Sure Don,

Here is the link for the radiator hose adapter [www.summitracing.com] Make sure this is the size of your hose. The bottom hose is a good place to install as Fred stated.

Here is the fan swich I use for Gen lll / 205 on 195 off [www.summitracing.com]

The parts are a little pricey but have worked well so far. I'm using Advanced Auto wire block and harness which has all the relays for the fan built in. If the car is off the fan will stay on until 195 degrees and then it will shut off. 20 seconds to a minute it shuts down. Will find out in the summer if it is longer.

I'm using a big single puller fan/ shroud combo from Summit also.



Edited 1 time(s). Last edit at 03/14/2011 05:55PM by 74ls1tr6.

Marvin - sensor itself can go directly into radiator hose, with wire "sealed" by hose clamp? Do you have part #/brand on sensor? Thanks.

Don, go to www.flex-a-lite.com for 31147. I put the sensor inside the hose with a minimal amount of sealer. No problems as yet. Marvin

Some 80s Saabs had the inhose thermostat like the summit one.

Most car manufactures put the temp sensors for guages, fan sensors, and computer in the top of the intake manifold or one of the heads. Putting it in the lower hose will measure the cooled water, not the actual temp of the engine. I used a temp sensor switch from a dodge omni in the intake manifold.

Hey Bill,

The whole idea of putting the sensor in the lower hose is to measure the cooled water.
The rad fan doesn't need to know the engine temp. It needs to know how the rad is doing.
A sensor in the intake manifold will only turn the fan on once the entire system has become too hot.
Kinda like cutting the lawn because the neighbours complained, not because the grass was too long.
This causes a lot of thermal stress on the engine as the fan switch tries to take over for the thermostat.
Also a miss match of the sensor and thermostat can cause the fan to run full time or turn on too late as the engine goes into a thermal runaway.
In some cases over heating will be caused as the fan turns on at hwy. speeds and becomes a restriction to air flow.
You can buy devices to avoid this problem or just put the sensor at the rad outlet and it fixes itself.
The OEMs didn't start to use in engine sensors until they had computer controls.And many reverted back to rad sensors until they got their ECU's up to speed.
The computer allows much finer control of the fans and most often incorporates the use of multi speed fans.
This was done mostly for fuel savings, climate controls and NVH issues.

Not bustin anybodys chops, it's just that I just do a lot of this stuff.

Cheers
Fred