Cummins 4BT & Diesel Conversions Forums banner
1 - 20 of 26 Posts

·
Registered
Joined
·
454 Posts
Discussion Starter · #1 ·
hi. time has come to get a thermo fan working on the effer. i have a couple of likely candidates for the fan switch. can i tell which is a temp switch for the fan from looking at it ?
 

·
Registered
Joined
·
854 Posts
It's doubtful that any of the switches that came on the engine would trigger a fan relay. Most are for the gauges, or else a monitoring system.

There are some aftermarket adjustable thermostats available. Make sure you use them to activate a relay, as the contacts inside the ones I have seen usually can't handle the full amperage loads a fan draws.

Also, surprisingly (and I have seen this debated to death on other forums) the correct position for the fan temp control is in the LOWER radiator hose.

Lastly, you shouldn't need much of a fan as long as you don't run much while not moving. What part of Oz are you in? How much warmer is it going to get in the next few months?
 

·
Administrator
Joined
·
4,180 Posts
Most of the 4BT P30 engines came with a thermo switch located on the lower radiator hose outlet. This switch was a "single pole normally open" which went to "closed" when it reached a predetermined temperature. To incorporate a relay in the circuit you would simply feed one side of this switch with a fused lead from the battery and take the other side of the switch to the "trigger lead" of the relay. Then you can run as much load as the relay(s) can handle. Remember to also properly fuse the hot side of the relay's feed wire from the battery.
 

·
Registered
Joined
·
808 Posts
I use NAPA Fan Switch Echlin FS 120. Turns on at 200 and off at 173.
Its a exact replacement for the fan switches used on the P-30 Engines I have bought. It is 1/2" NPT Male screw in and has 2 tabs for 1/4" push on connectors.

Wire it as Bob mentions thru a relay. I also add a toggle switch across the two posts on the switch and put the switch in the cab. This way, if
the fan switch fails, I can turn the fan on manually. I also put a pilot light on the dash that is fed directly from the fan power leads. This way, I know when the switch has closed and is sending power to the fan.

Paul
 

·
Registered
Joined
·
454 Posts
Discussion Starter · #5 ·
thanks guys. i'll have a better look. the thermo fan will also help when i finally get my finger out and put a/c on the sucker. linc, i am in western nsw. one christmas, we had a week of 47 deg. c.
 

·
Registered
Joined
·
854 Posts
one christmas, we had a week of 47 deg. c.
That's ungodly hot!
It doesn't even get that hot in this area of Texas!

You must be around Wentworth or Broken Hill area?
 

·
Registered
Joined
·
454 Posts
Discussion Starter · #7 · (Edited)
i am 200 k's west of Busted Hill, and about 300 roughly north of Wentworth. the town, wilcannia, where i live is on the darling river. this joins with the murray at wentworth.
 

·
Banned
Joined
·
427 Posts
i put mine where its supposed to be right next to the hot water out of the engine in the head . its where all 25 of my engines i,ve bought have them. never at the coldest point where water enters the engine on the bottom...
jmo
bob
 

·
Registered
Joined
·
854 Posts
i put mine where its supposed to be right next to the hot water out of the engine in the head...never at the coldest point where water enters the engine on the bottom.
You are thinking backwards - I can see it that way if your radiator is too small. The ONLY time you want the fan to come on is when the air through the radiator isn't enough to get the heat out of it. The only way to tell if that is happening or not is too sense what the lower hose temp is.

Sure, your way will work, too - - - but the electric fan will be running WAY more often that it really needs to, since it can't tell if the radiator is working like it should...

.... it can only tell if the engine is making heat or not.
In your scenario, lets say you have a semi truck radiator in front of your 4BT. Now you have plenty of radiator to handle the engine, but if you go up a big hill with a trailer, the fan switch senses the engine is making heat, so it kicks the fan on. It doesn't need to be on, but it can't tell since it isn't reading whether the temps in the lower hose are hot (fan needed) or cold (fan NOT needed)
 

·
Registered
Joined
·
14 Posts
I use NAPA Fan Switch Echlin FS 120. Turns on at 200 and off at 173.
Its a exact replacement for the fan switches used on the P-30 Engines I have bought. It is 1/2" NPT Male screw in and has 2 tabs for 1/4" push on connectors.

Wire it as Bob mentions thru a relay. I also add a toggle switch across the two posts on the switch and put the switch in the cab. This way, if
the fan switch fails, I can turn the fan on manually. I also put a pilot light on the dash that is fed directly from the fan power leads. This way, I know when the switch has closed and is sending power to the fan.

Paul
Thanks for the part number I looked thru the NAPA book and found a FS112 but it turned on at like 225 degress. It's all I could find at the time 200 would be much better. Thanks
 

·
Banned
Joined
·
427 Posts
i,ve got some H/D INDUSTRIAL fan control switches , on at 200 off at 175. no relay needed. and like i said all of my engines ( 18+ ) had the fan switch located near the thermostat on the cylinder head. none had them on the lower water inlet. same with every semi truck engine i,ve worked on in over 30+ yrs of being a semi truck owner/operator & mechanic.
JMO
BOB
 

·
Registered
Joined
·
808 Posts
Thanks for the part number I looked thru the NAPA book and found a FS112 but it turned on at like 225 degress. It's all I could find at the time 200 would be much better. Thanks
As far as I know, its still a good number. I have used it on 2 trucks and just bought one about 4 weeks ago for another 4BTA. I always go right to my NAPA store. He has had them on the shelf. In my opinion, I would never run a high current fan without a relay. I want the insurance of current carrying capacity.

Paul
 

·
Registered
Joined
·
915 Posts
I have a radiator mounted switch that mounts on the radiator tubes half way across. It may not be the best, but it works well. It kicks on when the engine gets to about 190 degrees.
 

·
Registered
Joined
·
28 Posts
I've always thought that the sensor was on the top hose as well along with the temp indicator. All the gassers I've owned with electric fans had them there. My NTC 400 Cummins has the fan relay (air switch), shutterstat, and temp guage switch all on top. I know because I've replaced all 3 of them. BUT what what Linc Tex says makes a lot of sence. The cooling capability of the rad varies a lot dependng on the outside temp and how hard you are working the engine. Pulling a long hill on a summer day in Texas with an air to air intercooler helping heat things up is going to cool the coolant a lot less than driving down the road in the winter in Alberta with no boost showing. Either way, the coolant going into the rad should be no different if the thermostat is working properly (190-195'F). If you have a sensor that turns on at 173"F, the fan would be running all the time. If you mount that sensor on the bottom rad hose, it only reads what temp the coolant is coming out of the rad at. That is going to vary greatly between the 2 previously mentioned senerios. If the rad can't cool the coolant down to at least 173'F, then the fan kicks in to help. Makes sence to me.
Ian
 

·
Banned
Joined
·
427 Posts
MY THERM SWITCHES ARE INDUSTRIAL QUALITY NOT THE LIGHT DUTY AUTOMOTIVE STYLE. and 91-v12 i, had alot better luck running a 180 thermostat in my 400 cummins engines. it was alot easyer on heads. they dont crack as bad from injector openning over to valve seats as bad.
jmo
bob
 

·
Registered
Joined
·
28 Posts
Actually I think you are right about the 180' thermostat in the 400. The shutters opened at 190 and the fan kicked in at 200. I'm sure the fan cut out again below 200 though otherwise it would still be running when the shutters closed at 190. Hardly ever had the fan come on though. It had to be a long pull up a mountain trail with low ground speed before the temp guage would get up that far. Those sensors were about $75.00 here in Canada if I remember correctly but if they eliminate the need for a relay, I think it's worth it.
Ian
 

·
Registered
Joined
·
180 Posts
You are thinking backwards - I can see it that way if your radiator is too small. The ONLY time you want the fan to come on is when the air through the radiator isn't enough to get the heat out of it. The only way to tell if that is happening or not is too sense what the lower hose temp is.

Sure, your way will work, too - - - but the electric fan will be running WAY more often that it really needs to, since it can't tell if the radiator is working like it should...

.... it can only tell if the engine is making heat or not.
In your scenario, lets say you have a semi truck radiator in front of your 4BT. Now you have plenty of radiator to handle the engine, but if you go up a big hill with a trailer, the fan switch senses the engine is making heat, so it kicks the fan on. It doesn't need to be on, but it can't tell since it isn't reading whether the temps in the lower hose are hot (fan needed) or cold (fan NOT needed)
Okay, this is going to kill me to say, but Bob is right about this one. If your engine cooling fan is not kicking on until your lower hose temperature is 200 degrees, how hot do you think the coolant is in your cylinder head?? In order to keep the temps in the engine (and specifically the head!) under control, you cannot allow your entire cooling system to get that hot. Stop and think for a minute; how are you going to be able to cool down a hot engine (especially if it's under a big load) with 200 degree coolant? I hate to be the one to break this to you, but there is no fan in the world that is electric or engine driven that will have any affect on airflow through your radiator above 45 mph. If you are going down the road, under load, above 45 mph, and your fan kicks on because the coolant temp exceeds 200 degrees ENTERING the engine, your cylinder head temps are likely in excess of 250 degrees. You can run your setup that way if you want, but when you have to replace your cracked cylinder head, don't spend too much time trying to figure out why it broke.
 

·
Registered
Joined
·
28 Posts
I agree 100%. What got me sidetracked was people saying the switch was an "on at 200, off at 173". If you're running a 180-185 thermostat, the coolant coming out of the engine should never get back down to 173 after the initial warmup. I always thought the switches were an on-off at whatever temp they were made for ie: 200'F switch closes at 200'F and above to turn on fan. Below 200'F the contacts are open and the fan is off. Please correct me if I'm wrong. While I'm no stranger to engines and working on them, I'm by no means a liscensed mechanic.
Ian
 

·
Registered
Joined
·
225 Posts
My biggest problem here is that my typing skills cant keep up with my thought process. But here i go anyway. My '97 4bta originally had the fan switch located in the coolant inlet elbow. While I was cleaning/painting/fixin stuff, I moved it to the pre thermostadt head location because it was just dumb to have it in the coolest part of the coolant system. The first time through this thread I didnt pay attn but i was bored this morning so I read it again. Now after 5 times, studying my truck, lot of thinking, I have to agree with Linctex that it should be in the coolant inlet passage.

The radiators job is to remove heat from the coolant. It does this by moving air through the radiator. I agree that 45+mph you shouldnt need a fan. However, at slower speeds it is the fans responsibility to provide that 45mph wind. The only way the fan has of knowing when to provide that wind is coolant temp. This reading needs to taken as close as possible to the fans work place which is the inlet elbow. If the coolant from the radiator is to hot,(not enough wind), the fan will come on and everything is hunkydory. After the coolant has passed completely through the engine does not tell the fan whether or not the radiator is getting enough "wind" or not. If your engine is getting hot by that point, then you have a problem with your coolant system,(low coolant, bad thermostadt, water pump, belt, etc.).

Now then, I also know that my fan switch that came on the engine turns the fan on at 195*. This will work fine if you keep it located at the thermostadt. If located in the coolant elbow, where it should be, it needs to be a cooler operating switch. I will have to do some testing but, after full warm up on a properly working system this switch located in the inlet elbow should come on maybe 15-20* hotter than normal coolant at this location. This will take some further discussion. I would appreciate all help on this topic because my thermostadt is sticking and when i go after it, I will be moving my fan switch. Ppfffew, now I have to find a new location for my heater hose return.
Carl
 

·
Registered
Joined
·
854 Posts
Okay, this is going to kill me to say, but Bob is right about this one. If your engine cooling fan is not kicking on until your lower hose temperature is 200 degrees, how hot do you think the coolant is in your cylinder head??
This is very easy to answer, and it is a detail that should have been discussed a little more first.

Naturally, the switch that goes in the lower hose is NOT a 200 degree switch. if my memory serves me correctly. It is around 170 or so on engine that run a 195 stat. I'll have to do a little checking on it, but it is around that number.

Bob Cowan, they may have been doing it for the last 30 years, but more and more engine/vehicle manufacturers are moving it to the lower hose. I believe all GM vehicles now have the fan temp switch at the water pump inlet.
 
1 - 20 of 26 Posts
Top