Primary and Secondary cooling fans cut in temperature

[FBS]

Hi everyone,  things are going well with the car. Summer is near and I am planning on taking a bit of a drive.  The cooling system has been flushed recently, car does not appear to have any overheating problems.  There is one thing though that bothers me.  I have a long steep 1 mile driveway.  Usually by the time I get to the top, temp needle is half way up and #1 cooling fan is on.  
i have yet to see the secondary fan cut in.  I check the fan motor and the motor relay and both work perfectly.  I have not checked the secondary fan Thermoswitch.  When does this fan kick in? At what temperature.  I’m considering installing a oil temp and water temp gauge so I can see the temps.  Can anyone enlighten me on the secondary fan operating characteristics?  Is there a way to  test is complete operation?  I have factory manual and could not find any definitive language on cut in temp and function. Maybe I am looking in the wrong area.  BTW I have both manuals.  Any help would be appreciated? 

[GoldStar]

Found it, page 7-17 where it shows how to check the thermosensors. In case you didn't know, the thermosensors are what actually provide the grounds for the fan motors. Looks like thermosensor 1 grounds at 185 degrees, and thermosensor 2 grounds at 212 degrees.

[TexasQuest]

When I still had the factory thermosensors in my car, the secondary fan would come on a lot later than the primary. I switched it out to another primary sensor and ran a jumper wire between the two for added reassurance. 

[FBS]

That makes sense to me.  I noticed yesterday while I was driving that even though the outside air temp was about 95 Degrees... the cooling system temp gauge was only slightly warmer than normal when the outside temp is in the 60's to 70's.   I like Texas Quests idea, I am wondering how that worked out.  That would mean both fans come on at the same time. But still I also wonder if thats how Mitsubishi designed it why change it as long as its working correctly.   I have never seen the primary fan come on other than me driving up my driveway which is steep and I dont go to fast.  It did not even come on while driving around town at 95Degrees air temp. 

Edited April 29, 2023 by FBS

[GoldStar]

I did the same, but I didn't run a jumper wire. I can't speak for the stock fans, but my two aftermarket fans coming on at the same time maxed out the capacity of the stock alternator. I've upgraded to a 90 amp alternator to compensate. Cools quickly, though, they aren't on for long.

[techboy]

On my car I grounded the 2ndary fan to the battery so it's on all the time. Primary still works as normal. I only drive the car during the summer months so it's a nice setup for me.

[kev]

Over the years I found that if I was retaining the electric fans, I ALWAYS ran both hot, at all times, by grounding both lower wires that went to the t-stats.   My view is that I'd rather tax the alternator than risk overheating.   These t-stats always fail with time.   As we all know, it doesn't take much overheating to crack these heads.    

But my advice is to dump the electric fans and use an early model clutch fan setup.   I've had no issues with failing fan clutches in over 30 years, never have overheating issues, etc.   Although if you have an aluminum radiator (cxracing, etc.), then using the clutch fan/shroud is a bit more difficult.  There was a member here who figured out how to do it, but his thread was lost in the database issue.   

[FBS]

On 5/1/2023 at 6:18 AM, kev said:

Over the years I found that if I was retaining the electric fans, I ALWAYS ran both hot, at all times, by grounding both lower wires that went to the t-stats.   My view is that I'd rather tax the alternator than risk overheating.   These t-stats always fail with time.   As we all know, it doesn't take much overheating to crack these heads.    

But my advice is to dump the electric fans and use an early model clutch fan setup.   I've had no issues with failing fan clutches in over 30 years, never have overheating issues, etc.   Although if you have an aluminum radiator (cxracing, etc.), then using the clutch fan/shroud is a bit more difficult.  There was a member here who figured out how to do it, but his thread was lost in the database issue.   

Hi Kev... thanks for your reply...  The thing is that everything is working really well on the car.  I dont really want to re-engineer the car just yet.  But I see what you are saying.  The #1 fan never comes on while driving on the highway...which is 90% of what I would drive, even when it was 95Degrees...Coolant temp is not reaching 185Degrees so car is staying pretty cool.  Anyhow I think the least I will do is get new thermostats.. for both fans.  

[kev]

For now, immediately unplug the wires going to the t-stats and ground them (well at least to the secondary that you know isn't functioning).  This will make the fans run at all times when the key is ON.    Don't drive it any further until you do that...you know you have a t-stat issue and it isn't worth cracking the head.    Yes, replace the t-stats and consider at least what techboy has provided (ground the secondary fan).   I, personally, would just leave both grounded and running all the time.   One of my cars has been running like that since 2002 (two owners later, it still is wired the same).   If you insist on using the stock t-stats, connect a wire between the two t-stats....thus if either one fails, the other will still turn on both fans.     The factory electric fan setup is a design failure on our cars IMHO.  You can address this easily by what we are saying without altering the stock appearance of the engine bay.  

Also, the 'mod' I suggested isn't a mod.  It's simply resorting to the much more reliable setup on the earlier model starquests (83/84).   I've never had a cracked head on a car running the factory earlier model clutch fan setup.   You would need the fan shroud out of an 83/84 starquest and the clutch fan itself out of the same years or from any 80s Montero or Mitsubishi pickup (they had the same fan but a different shroud).     The only difficult thing is that the later model radiators had the three brackets brazed to them to mount the electric fans (two small ones on the bottom tank near the t-stats and one larger double bracket on the top tank in the middle).   Just a little heat from a propane or MAP torch and the brackets come off the radiator without damage and could easily be soldered back on later down the road.   The clutch fan shroud simply bolts on with the four bolts on the sides of the radiator (same ones used on the other sides of the electric fans).    For the clutch fan itself, just remove the four bolts holding the water pulley pump.  Remove the flat plate over the pump pulley and bolt on the clutch fan.   The water pumps all have provisions for clutch fans even for electric fan cars (they have the 'nub' that protrudes into the fan to engage the clutch).      The 83/84 models used studs instead of bolts on the water pump connection.  Studs make it easier to mount the clutch fan but I simply reuse the four original bolts.      I should note that the 83/84 clutch fan shroud is two pieces.  You bolt the lower half on the radiator first (the radiator doesn't have to be out of the car or even disconnected).   Then put on the clutch fan and, last, bolt on the top half of the shroud.   The top half is easier with the upper radiator hose disconnected but you can still get in there with it connected.   

 

Again, don't even start the vehicle until you get that secondary fan working (Ground the wire...takes less than two minutes)!   I can't stress this enough!    Take this from a guy who has been driving these cars for over 30 years and has cracked many cylinder heads (yes, I've cracked a head without ever noticing an increase in temperature on the stock gauge).   I'm so paranoid about this that I've wired the fans to ground on the day of purchase of starquest in the former owners driveway before driving it home....he looked at me like I was crazy!  

 

kev

[FBS]

Hey Kev... thanks for the inspiration... I decided to take your advise.  I grounded both fans with one little change.  I added a simple switch inline on the second fan so I can turn it off if I want to.  When in off position it is defaulted to normal operation.  I replaced the Thermoswitch and it works correctly.  Cheaper to replace fan than head and a lot less work.  Thanks for your effort and sharing your experience.. I really appreciate it.

 

[FBS]

On 5/3/2023 at 7:19 AM, kev said:

For now, immediately unplug the wires going to the t-stats and ground them (well at least to the secondary that you know isn't functioning).  This will make the fans run at all times when the key is ON.    Don't drive it any further until you do that...you know you have a t-stat issue and it isn't worth cracking the head.    Yes, replace the t-stats and consider at least what techboy has provided (ground the secondary fan).   I, personally, would just leave both grounded and running all the time.   One of my cars has been running like that since 2002 (two owners later, it still is wired the same).   If you insist on using the stock t-stats, connect a wire between the two t-stats....thus if either one fails, the other will still turn on both fans.     The factory electric fan setup is a design failure on our cars IMHO.  You can address this easily by what we are saying without altering the stock appearance of the engine bay.  

Also, the 'mod' I suggested isn't a mod.  It's simply resorting to the much more reliable setup on the earlier model starquests (83/84).   I've never had a cracked head on a car running the factory earlier model clutch fan setup.   You would need the fan shroud out of an 83/84 starquest and the clutch fan itself out of the same years or from any 80s Montero or Mitsubishi pickup (they had the same fan but a different shroud).     The only difficult thing is that the later model radiators had the three brackets brazed to them to mount the electric fans (two small ones on the bottom tank near the t-stats and one larger double bracket on the top tank in the middle).   Just a little heat from a propane or MAP torch and the brackets come off the radiator without damage and could easily be soldered back on later down the road.   The clutch fan shroud simply bolts on with the four bolts on the sides of the radiator (same ones used on the other sides of the electric fans).    For the clutch fan itself, just remove the four bolts holding the water pulley pump.  Remove the flat plate over the pump pulley and bolt on the clutch fan.   The water pumps all have provisions for clutch fans even for electric fan cars (they have the 'nub' that protrudes into the fan to engage the clutch).      The 83/84 models used studs instead of bolts on the water pump connection.  Studs make it easier to mount the clutch fan but I simply reuse the four original bolts.      I should note that the 83/84 clutch fan shroud is two pieces.  You bolt the lower half on the radiator first (the radiator doesn't have to be out of the car or even disconnected).   Then put on the clutch fan and, last, bolt on the top half of the shroud.   The top half is easier with the upper radiator hose disconnected but you can still get in there with it connected.   

 

Again, don't even start the vehicle until you get that secondary fan working (Ground the wire...takes less than two minutes)!   I can't stress this enough!    Take this from a guy who has been driving these cars for over 30 years and has cracked many cylinder heads (yes, I've cracked a head without ever noticing an increase in temperature on the stock gauge).   I'm so paranoid about this that I've wired the fans to ground on the day of purchase of starquest in the former owners driveway before driving it home....he looked at me like I was crazy!  

 

kev

Hey Kev... thanks for the inspiration... I decided to take your advise.  I grounded both fans with one little change.  I added a simple switch inline on the second fan so I can turn it off if I want to.  When in off position it is defaulted to normal operation.  I replaced the Thermoswitch and it works correctly.  Cheaper to replace fan than head and a lot less work.  Thanks for your effort and sharing your experience.. I really appreciate it.

[BlueCuda]

I came super close to buying one in Austin and driving it home a few years ago.  It ran and drove but it had been in storage for years.  I had a plan to change the front tires, the fluids, and drive it home about 8-10 hours.  In the end I didn't trust that someone had put a mechanical fan on it because I had never seen one converted like that.  Little did I know...... 

[kev]

Good to hear.  Although, I don't know what the manual switch gives you.   By the time you realize it is getting too hot and need to flip the switch, it may be too late.    Remember, it takes a bit of time for the gauge to register the increase in temperature.    Why not buy two new 'primary' t-stats, install them, connect them together and then to the secondary fan only and keep the primary grounded at all times.   Or vice versa for that matter (like techboy mentioned).    This way one would be on for sure and the other would have to have two t-stat failures before it would stop working.      

Another thing that I never really experimented with is that the automatic cars have a better secondary fan.  It is closer to the primary fan design.   I never really noticed this until recently despite owning two automatic cars over the years.    Someone mentioned it on here and the light bulb went off in my head haha.   There had to have been a reason why the automatics had a different secondary fan than the manuals.  On a similar note, I never understood why the AC condenser was a different design between autos and manuals as well.  

kev

[FBS]

22 minutes ago, kev said:

Good to hear.  Although, I don't know what the manual switch gives you.   By the time you realize it is getting too hot and need to flip the switch, it may be too late.    Remember, it takes a bit of time for the gauge to register the increase in temperature.    Why not buy two new 'primary' t-stats, install them, connect them together and then to the secondary fan only and keep the primary grounded at all times.   Or vice versa for that matter (like techboy mentioned).    This way one would be on for sure and the other would have to have two t-stat failures before it would stop working.      

Another thing that I never really experimented with is that the automatic cars have a better secondary fan.  It is closer to the primary fan design.   I never really noticed this until recently despite owning two automatic cars over the years.    Someone mentioned it on here and the light bulb went off in my head haha.   There had to have been a reason why the automatics had a different secondary fan than the manuals.  On a similar note, I never understood why the AC condenser was a different design between autos and manuals as well.  

kev

I put the manual switch on it because the cooling system is actually in really perfect shape other than that one thing...There is not a real need to run both fans all the time..I will use it when I have to come up the hill I drive up that is the only time I see any real change in engine temp.  It does not have to make sense to everyone else.. I get why it seems pointless.. but not for me... I appreciate all your valuable input.. 

[Tim_C.]

I would never run both fans all of the time. That's a band aid on a broken arm. With a properly working cooling system, you rarely need the first fan, let alone the 2nd. Fix whatever problem is causing the temp to rise before touching anything else. 

At most, you can run the 185 thermosensor in both locations or wire the secondary to come on with the primary but I never needed that after having the radiator professionally gone through. 

[techboy]

It is hard to find people to re-rod radiators these days, but that's what I had done to my rad when I restored my car. Haven't had any cooling issues. If you can find someplace to have rad gone through I second that.

[FBS]

On 5/12/2023 at 8:41 AM, Tim_C. said:

I would never run both fans all of the time. That's a band aid on a broken arm. With a properly working cooling system, you rarely need the first fan, let alone the 2nd. Fix whatever problem is causing the temp to rise before touching anything else. 

At most, you can run the 185 thermosensor in both locations or wire the secondary to come on with the primary but I never needed that after having the radiator professionally gone through. 

I would tend to agree with you on this.  I talked to my father who I got the car from.. He had the entire cooling system cleaned out before I got the car.  The car never overheated.  Radiator looks really clean.  Thanks for your input on this.