Electric Fan Control

[PJ Moran]

I have a dual 11" Spal setup and it's controlled by a simple 195 degree thermal switch in the water neck.  I have driven the car little up until recently, and it's all been just around town.  It has worked just fine.  The car will idle forever with the fans coming on and off as the temperature switch does its thing.

This weekend, I took the car out on a coupla "extended" drives in pretty (70's) weather.  On the highway, the car kept pushing the 205 - 210 degree mark - somewhat higher than the switch's setting of 195 degrees.  I would expect the car to run closer to 180 than to 210.  I suspect the fans were running all the time, and that's nonsense.  I've read that the fans can actually reduce the airflow through the radiator (but I'm a little incredulous on that one).

My radiator may be inadequate.  It's the 24" "big block / AC" radiator with a 3-row core.  I figured it would be more than enough.  Maybe it's not.  It was with my old 289, but this 408 may be generating more heat.  I also have factory air, but that was not running.

Regardless, I don't need the fans coming on if I'm driving over a certain speed.  I have an electronic speedometer and was wondering if there was some kind of controller that used vehicle speed as part of the fan control.

[Midlife]

At speed, you shouldn't need a fan at all.  Usual problems of overheating at speed are:

Bad water pump
collapsed radiator hose
blocked radiator

[PJ Moran]

At speed, you shouldn't need a fan at all.  Usual problems of overheating at speed are:

Bad water pump
collapsed radiator hose
blocked radiator

I think you may have hit upon something.  The water pump is a new, Ford,  high performance aluminum version.  The radiator is not blocked.  But, the lower hose is one I built out of two other hoses (three pieces) using unions.  There is no spring inside to keep it from collapsing.  That might be the culprit.

I still want to disable the fans at speed, though...

[buening]

If you have a thermostat rated below when the fans kick on, then the fans should not be on while driving at speeds....assuming you have fixed the collapsing lower hose issue.  Driving at speeds should keep it below the fan turn-on point and should stay around the thermostat rating.

[apollard]

I still want to disable the fans at speed, though...

Think about that alot before you do it. Get the system right, and it will stay off at speed. Then, when something goes wrong again (hose spring collapses?), it will still come on at speed to help with the cooling. Unless you disable it. A running fan still moves more air than just the pressure in front of the rad.

No factory car I know of disables the fan at speed - only controls it on temp. I have two BMWs,  both use engine control module to control the fan and neither disables the fan at speed. The work truck either (tested that one!).

[Fast68back]

I have a dual fan setup and my car, even in summer runs right at 180 on the highway, my fans dont kick on until after 180, its adjustable so I have them coming on around 185/190, it may even be a little higher than that.

[PJ Moran]

Well, something has changed.  When idling, instead of cycling between 180 and 195, fans coming on and off, it warms up to about 200 and stays there.  The fans stay on, of course, since the temp switch is 195.

The lower radiator hose is not collapsing.  Even when revved to 3000 rpm.

Could this be a thermostat going bad?  Do they get progressively worse with time or usually fail suddenly?

[johnpro]

It could very easily be the thermostat, but I think the bigger culprit is having the sensor in the t-stat housing.  Yes, we all have to do what we have to do, but that is not the ideal place for it.  The ideal place is in the return hose back to the engine.

[buening]

This may sound dumb, but are you sure the fan is blowing the correct way? 

[PJ Moran]

It could very easily be the thermostat, but I think the bigger culprit is having the sensor in the t-stat housing.  Yes, we all have to do what we have to do, but that is not the ideal place for it.  The ideal place is in the return hose back to the engine.

I disagree.

If the radiator is keeping up, the stat is controlling the temperature.  Once the radiator starts losing ground, the stat is wide open and the temp keeps rising.  So, measuring the temp at the stat is a good indicator of what's going on.  When the temp there is significantly higher than the stat's rating, you know the radiator needs some help.

In my experience, coolant temperature sensors / switches in computer controlled engines are located near the water neck or in the cylinder head.  None are in the radiator outlet...

[PJ Moran]

This may sound dumb, but are you sure the fan is blowing the correct way? 

Not dumb at all.  When I first fired the engine, I noticed that the fans weren't terribly effective during idle.  After a little poking around, I discovered that one fan was pushing and one was pulling.  I had switched the wires in one of the connectors by accident.  After fixing that, the fans brought the temp down very quickly and the cycle worked perfectly.

Problem is that now the fans don't pull the temp down even at idle, and they never go off.  I thought Mid had hit the nail on the head with the collapsed hose theory.  But, a faulty thermostat would cause the same symptoms as I see it.

I think I'm off to the parts house tomorrow for a new 'stat.  Fortunately, that's a relatively easy fix.  A water pump, especially with my March serpentine setup, would be a nightmare!

[buening]

Just making sure.  Sometimes it's the easy stuff that we overlook, so I always throw those suggestions out there  :lol

One thing that can happen when the sensor is in the water neck is a steam pocket can occur if there is air in the system, which will give a faulty high temp reading on the gauge.

[johnpro]

I disagree.

If the radiator is keeping up, the stat is controlling the temperature.  Once the radiator starts losing ground, the stat is wide open and the temp keeps rising.  So, measuring the temp at the stat is a good indicator of what's going on.  When the temp there is significantly higher than the stat's rating, you know the radiator needs some help.

In my experience, coolant temperature sensors / switches in computer controlled engines are located near the water neck or in the cylinder head.  None are in the radiator outlet...

We're going to have to agree to disagree on this one.  The important thing is the temperature of the water entering the engine.  Not the temp coming out.  If the temperature coming out of the radiator is low enough, the culprit will NOT be the radiator.

[apollard]

In my experience, coolant temperature sensors / switches in computer controlled engines are located near the water neck or in the cylinder head.  None are in the radiator outlet...

The primary goal of ECT sensors is to measure the engine operating temperature - for mixture & spark control calculations. Controlling the cooling fans is a secondary function; only one sensor is used for cost reasons. Engine operating temp is best determined where the coolant leaves the heads (ie, near the outlet).

Some vehicles use two sensors - one in the coolant outlet, one in the coolant inlet. The wife's X5 is such a vehicle. According to the BMW info I've read, the coolant inlet temp is used to control the fans, and can be overridden by the coolant exit temp - if the computer decides the inlet temp is bad.

[PJ Moran]

If the temperature coming out of the radiator is low enough, the culprit will NOT be the radiator.

I agree with this statement.  As a diagnostic tool, one could put a temperature probe in the lower hose and see if the radiator is working.  That would direct attention to other areas such as the water pump or thermostat.  But, I don't think that's the place to put a fan control switch.  That needs to be in the stat housing.

In Mid's post he said, "blocked radiator".  I immediately ruled that out because "blocked" to me meant externally - as if shielded from airflow somehow.  But, he might have meant internally "blocked" (clogged is the word I would have used ;) ).  That's a possibility, I suppose.  It's literally the only piece in my engine compartment that isn't new.

I'm going to drain the system and swap out the thermostat.  I'll take a peek into the radiator for signs of "blockage" :).  If the stat doesn't fix it, the radiator's coming out for a cleaning.

The thing to remember is that this problem has slowly developed over the last coupla months.  When I first got the car on the road, it was as cool as a cucumber.  Each time I've taken it out lately, the temp gage reads a few degrees higher.  Sounds like the radiator is getting progressively more clogged or the 'stat is gradually going out.

[AzPete]

Why not just go ahead and have the radiator cleaned and checked anyway. If it is the only thing not done new, then it is old and could be the weak point in a month....... I hate buying coolant twice in a few months.

[buening]

The thing to remember is that this problem has slowly developed over the last coupla months.  When I first got the car on the road, it was as cool as a cucumber.  Each time I've taken it out lately, the temp gage reads a few degrees higher.  Sounds like the radiator is getting progressively more clogged or the 'stat is gradually going out.

Sounds like a good time to have the radiator rodded by the local rad shop  :ecit   The 'stat is an easy change though, but while you have the fluid drained it wouldn't hurt having the radiator cleaned as well

[Midlife]

In Mid's post he said, "blocked radiator".  I immediately ruled that out because "blocked" to me meant externally - as if shielded from airflow somehow.  But, he might have meant internally "blocked" (clogged is the word I would have used ;) ).  That's a possibility, I suppose.  It's literally the only piece in my engine compartment that isn't new.

Good point!  I meant air flow is blocked.  A clogged radiator would cause an engine to overheat at idle or slow speeds as well.

[daveSanborn]

But, I don't think that's the place to put a fan control switch.  That needs to be in the stat housing.

I'm going to jump in with both feet and agree wholeheartedly with JohnPro on the placement of the fan temp sensor.

I'm sorry, you haven't thought this through....

As an example:

At 70 MPH on the open interstate, let's say your coolant temperature exiting through the T-stat is 200 degrees.  This will trigger your Efans to energize.  But.... the airflow going through the radiator at 70 MPH would have been enough to cool the coolant below 180 WITHOUT the fans energizing.... so under this circumstance your fans are energizing for nothing... and even possibly disrupting airflow through the radiator.

The purpose of the fans is NOT to keep coolant within the RADIATOR at or below the desired temperature setting.... their purpose IS to keep coolant entering the ENGINE at or below the desired temperature setting.

Placing the fan temp sensor switch either within the lower (radiator outlet) hose or within the radiators tank at a location just prior to coolant entering the outlet hose is the 100% perfect location.

Ask any expert, just be careful you're not talking to a clueless salesman.

http://www.becool.com/

http://www.griffinrad.com/


Now, on to trying to identify your problem.....

What has changed.... other than the increase in operating temperature..... between this year and last year?  Tire size?  Rear gear ratio change?  New spark plugs?  Different oil?  Anything?

[tarafied1]

My e-fan's temp control instructions recommended putting the probe on the exit side of the radiator also.

[PJ Moran]

I'm going to jump in with both feet and agree wholeheartedly with JohnPro on the placement of the fan temp sensor.

I'm sorry, you haven't thought this through....

The purpose of the fans is NOT to keep coolant within the RADIATOR at or below the desired temperature setting.... their purpose IS to keep coolant entering the ENGINE at or below the desired temperature setting.

Placing the fan temp sensor switch either within the lower (radiator outlet) hose or within the radiators tank at a location just prior to coolant entering the outlet hose is the 100% perfect location.

If the cooling system is up to the task, the water temperature just past the ‘stat should be at or only slightly above the opening temp of the ‘stat.  The ‘stat keeps water in the engine and only lets it out when the minimum temperature has been reached.  If the incoming water is cool enough, the ‘stat will regulate flow and never go to wide open – it is constantly modulating.  As the water temperature increases beyond that point, the stat goes wide open, and it is clear that the cooling system is struggling to keep up.  The engine is putting more heat into the water than the radiator can take out.

With electric fans, you get to help the radiator by increasing airflow and bring the coolant temps down.  Either the radiator can handle it by itself, or it needs some help from the fans.  Of course, the fan benefit depends mostly on how fast the car is moving.  Slow = high benefit.  Fast = no benefit.

So, by measuring the temp at the ‘stat, you can tell when the radiator needs some help.  When the temp there reaches a point significantly above the ‘stat opening, the radiator is clearly not doing enough – you need the fans to come on.

My ‘stat is a 180.  My switch is a 195.  So, if the water coming out of the engine hits 195, it’s clear that the ‘stat is wide open, the radiator is not keeping up, and the fans need to come on.

When sitting still, the difference between inlet and outlet temps on the radiator will be small.  With vehicle speed, the difference will increase.  What this means is that fans switched via ‘stat temps will come on sooner than those switched by outlet temps (assuming you use the same temperature setting).  And the delay will increase with vehicle speed.

If you use the same temp switch at the outlet, then you’re letting the engine get hotter before energizing the fans.  So, you have to use a lower setting if measuring at the output to equally protect against overheating.  Now you have to estimate what the temperature drop across your radiator is.  That varies with ambient temperature and vehicle speed.  So, how are you supposed to pick a setting when there are so many variables at play?

I’m sure that some manufacturers tell you to put their probes/switches in the outlet.  Spal tells you to put theirs in the cylinder head or intake manifold.

Based on my understanding of how the cooling system works (outlined above), I still think that the ‘stat housing is the ideal location for the temperature switch.  If the temperature there is too high, the cooling system is underperforming, and the reasonable action is to turn on the fans.

Now, if the fans are already on and the temp isn’t dropping, then you have other problems (like me) such as stuck ‘stat, collapsed hose, or clogged/blocked radiator.

I could be wrong – I haven’t thought this through very well  :)

[buening]

I can see both sides of the argument.  The temperature gradient will vary depending on the motor size and cooling system. I'd be curious to see how much different inlet and outlet coolant temps are.

Let say that the coolant at the thermostat is 195° but your radiator is huge and you have very high flow e-fans. E-fan sensor is set up to kick the fans on at 195° and is placed in the thermostat. With the fans running and the car in traffic, the temperature of the coolant exiting the radiator could be 170° or so (for example).  Inlet temps are lower than recommended operating temps, but as the fluid passes through the motor it is heated up until it reaches the end of the system where it is again 195°.  Average engine temp would be 178° approximately in a perfect world, but doesn't take into account fans running to the point of their turn-off temperature.

The reverse can happen if the fan sensor is in the lower hose.  Coolant exiting the radiator is 195° (based on fan kick-on setting) and as it passes through the engine it is heated up.  Assuming the same temperature gradient, you'd be up to 210° at the thermostat. Average engine temp would be 203°.  

In my opinion, one needs to adjust when their fans kick on depending on the location of the sensor.  Any flaws in my rationale?  If the temp difference of outlet and inlet coolant is small, then all of this location of the sensor talk doesn't matter.

[PJ Moran]

I pulled my 'stat (a Mr.Gasket high-performance model).  I tested it in a pot of boiling water and could see nothing happen.  I got a new Stant 'stat and performed the same test and saw it promptly open wide.

I installed the new 'stat and tried it out.  The engine warms up, fans come on, engine cools, fans go off.  Lather, rinse, repeat.

On a road test, the gage stays at 180 except when at a light.  While cruising, it sat on 180 the whole time.  It would rise a coupla degrees when I got on it really hard, but...

So, I guess my old (new) 'stat was on it's way out.  Everything looks fine, now.

[AzPete]

Good deal.

All that talk for a r&r of a t-stat. Amazing what one little part can bring out for a discussion around here. All is good.

[apollard]

I can see both sides of the argument.  The temperature gradient will vary depending on the motor size and cooling system. I'd be curious to see how much different inlet and outlet coolant temps are.

Heh. I've actually done this one. I put efans on my Dodge tow vehicle. Obviously, towing 5000# (11,500 GVW) through the mountains, I was very concerned about the ability to cool the beast.

Before I put them on, I had a temp differential (engine outlet vs inlet) of 40 degrees (ambient was around 80F). This was with a 24"!!!!! engine driven fan (clutched, of course). When that clutch kicked in, it sounded like a freakin' jet taking off

I installed the efans; the fans are controlled based on radiator exit temp. I adjusted to have them maintain about the same temp differential at idle as the stock fan - so they will only run when the temp of the radiator exit rises above 160 or so. This gave me an average maintained temp differential of ~45F.

After efans, I got about 65 degree differential right when the fans cut off- so, better cooling at idle. In other words, they cut on at 160 engine inlet temp, and off at 135. Having no way to test under load, that idle test gave me the confidence to try it out. Slow speed towing was OK, high speed was OK, so off to the mountains I went - with the old fan in the bed, just in case.

While towing (outside of the mountains) I run about 195 on the engine, no matter what - and the fans never cut on. Sitting in traffic, it hits ~205, then the fans cut in, and it cools down. Pulling long hills in the mountains, the fan stays constantly, then will cut off going down the next hill. Engine temp rises to 215 pulling hills. Pretty much what it did with the stock fan & clutch. No issues so far.

When not towing, they only cut on when idling for long periods.

Based on the fact that the fans stay off when towing on "flat" land, I'd say it's running somewhere around that 50-60F differential at speed.