In most OEM applications they don't turn the fan at at the t-stat opening temp.  Typically the fans are delayed until the coolant temp is more like 210-220 degrees.  So long as the engine doesn't overheat, which at typically system pressure of say 13-15psi wouldn't be until like 240-250 degrees, a hotter running engine is inherently more efficient.  I think the OEMs do it that way to increase efficiency/reduce emissions.  

If you are maintaining engine temp of 195 I see nothing wrong with it.  I have mine (single fan) set to come on at 200.  I drove the car once when it was 100 degree outside with a heat index closer to 110 just to see what would happen, and it never got above 215, even sitting idling in traffic.  

MS wrote:

I was wondering if I should bump up the start point to 200. I just don’t want the engine temperature to go higher than 195. But, it seems like with set point at 195, if the thermostat is open, the fans will be running.

Maybe fans would shut off more if set point was higher?

What are you using to control your fans? How adjustable is it? Some controllers allow for hysteresis, while others are just on at X temp and off at Y.

Do they cycle on/off a lot now? If you set for 200 it will most likely go over that for a bit until the fans get the water temp back down.
 

MS wrote:

I have the Davies/Craig digital controller. Fan #2 comes on ten seconds after fan #1. It is programmable in one degree increments to set the start point. It runs until the radiator temperature is reduced to ten degrees below the set point.
Both fans run when AC compressor is on.

The set point can be programmed as high as 220 degrees.

Rather than moving the on temp of the 1st fan, I would experiment with the 2nd fan turn on point. 

Fan delay is not adjustable. Set at ten seconds for start of second fan.

I wouldn't worry about the engine temperature exceeding 195 degrees.  The engine will actually last longer running hotter, as well as making more power, and getting better fuel economy.  I'd be more concerned that the temperature doesn't creep up from the set point and get to a point where I would consider it to be too hot (which would be about 220-230 degrees).  With a good set of fans I find that decidedly unlikely.  

It could also be the water pump.  If your radiator is aluminum, which I believe the Champion ones are, 2 rows of 1" tubes is pretty much standard.  They typically don't use 3 rows of tubes, because aluminum is much better at rejecting heat that copper/brass.

A water pump with the wrong pulley ratio, or one that's very high volume that moves the coolant through the system too fast, can cause the coolant not to be in contact with the block, heads, etc. long enough for optimal heat transfer.  I did some experimentation with my geothermal heat pumps and found that unregulated the "dumb" systems (ones that have no internal flow control) would run so much water if not chocked down that the outgoing temp was well below the spec'd temp delta (incoming temp vs. outgoing temp), which is supposed to be 20-25 degrees rise in cooling.  I was seeing more like 15-17 degrees.  By partially closing a ball vale in the return side and reducing flow down to 1.5 gpm/ton, or closer to that spec, my outgoing temp went up to 22 degrees and the systems cooled better and ran less.  Unregulated I could see 8-9gpm on the 3 ton unit, which I cut down to 5.5-6 gpm.  Fairly minor change, but significant difference in system performance.  

IMO a stock engine shouldn't need a high volume water pump, much like a high volume oil pump.  These changes are unnecessary and fall into the "bigger MUST be better" camp of engine building.  What you may have done by adding another fan is decrease the temperature of the air around the core, or at least increase it ability for the heat to be carried away.  Consider that heat transfer in a given time period is greatest when the difference in temperature between the two mediums is greatest.  

You could test this if you could change the water pump pulley size.  Increase the size and spin the pump slower and see what effect it has on the temperature both with and without the new fan running.  Reducing the size of the crank pulley would also work, but would also impact the speed at which any other accessories spin (alternator, AC, PS, etc.).  

I run a 3 row copper/brass radiator and a stock replacement iron water pump with a single SPAL fan and a 195 degree t-stat.  Never had an issue with that setup getting hot in the summer, and actually adjust my fan on setting up in the winter to avoid it running too cool.  

I didn't "technically" read every word of every reply, but I did try to skim them looking at the conversation.

Here is what you want.  When you're cruising on the open highway and the natural air flow through the radiator is keeping the temperature steady just above the t-stat setting (say steady at 200), you do not want the electric fans running.  No reason for those fans to be running.  So I agree with the advise you've been given to turn the fans back OFF at 205 (at least) for a 195 t-stat.  I probably wouldn't turn the fans on until 215 or so (10 degrees higher than the 205 turn off temp).  Hopefully, your fans won't be running all the time.

Edit:  I only just read the post right above mine.  Wiring the fan to run all the time will just result in the continuous running of the electric fan motor and the continuous generation of the power needed to run it by the alternator.  If you are good with this, then the wiring could definitely be simple and basic.

Last edited by Rufus68 (7/10/2025 7:55 PM)

Update:
I changed the fan setting from 195 to 200 for the fans to come on. The result was the temperature gauge then read 200!!
So, I reset the fans to come on at 194, and now the gauge reads just at 195 or below.
End of experiment

Raymond_B wrote:

MS wrote:

Update:
I changed the fan setting from 195 to 200 for the fans to come on. The result was the temperature gauge then read 200!!
So, I reset the fans to come on at 194, and now the gauge reads just at 195 or below.
End of experiment

Yeah, my reply was based on you saying "That seems to be working perfect." so I did not figure you wanted higher temps. I stand behind my original observations that "you nailed it"
 

  Mine did the same thing,   I tested it through Culvers drive through on a busy day....LOL    I changed my back also.  I keep it 180 highway cruising and under 200 in the city.   Then mine kicks on and off when the AC is on at hwy and city driving.  
 

Wait until you see my yellow spark plug wires.

So, you can put that experience behind you!  Guessing that you can relax a bit and move on to another project ... hopefully not as challenging as that one. 
 

MS wrote:

Learning curve is over.   The 69 went home with a new owner today.

 
Whomever purchased it, definitely got a well running Mustang.

Now you can focus on the convertible.

Last edited by Nos681 (7/17/2025 7:21 PM)