What's actually making your engine run hot

For years I've seen a nearly constant supply of social media posts with people complaining that their engine is running hot and automatically assuming that they need to upgrade to the biggest radiator and largest water pump they can find. 

Which is the wrong thinking most of the time.

So I finally made a little video about what could actually be causing the problem and ways to build head room into a cooling system.

Some additional information: My car originally ran at low 200s (street) and upwards of 230F (track) with the same radiator and fan setup with a decent tune. With the mods I talk about in the video it now runs only 170-185 on the street and almost never breaks 195 on track.

This is a great resource, as well ==> https://www.professionalawesome.com/cooling-system-radiator-technical-information/

I inherited my '67 Le Mans from my mother.  My older sister had wrecked it once and in replacing the front fascia, we were unable to source the fan shroud.

The car always ran a little hot, and we assumed that was the reason...

...until I happened to do points and plugs on it.  Timing was way advanced.  Fixed that and it fixed the overheating.

I remember when Hot Rod Mag did the Hot Rod Rescue column and so many were overheating issues, and very frequently it was "Timing was too advanced". Timing actually effected a lot of stuff that you wouldn't necessarily think of.

I suspect my Dart's fans are undersized, but now I wonder if a bit more tuning may also help. Thanks for sharing. 

NickD said:

I remember when Hot Rod Mag did the Hot Rod Rescue column and so many were overheating issues, and very frequently it was "Timing was too advanced". Timing actually effected a lot of stuff that you wouldn't necessarily think of.

A joke I've read in classic car circles are 90% of carburetor problems are ignition related. 

Good video and link but neither address the thermostat.  Modern thermostats start opening around 195* +/-.  That means that it is unlikely that your car's cooling system temps will ever run lower than 195* on track.  I have had very good results installing a 180* thermostat in track and race cars.  The 180* thermostat results in a minimum measured temps of a little over 180* on track and overall lowers the maximum observed high temp.  

If your engine adds 10-20* of heat driven in anger on track, you need the starting point of the cooling to be lower - sending all of the coolant through the radiator starting at 180* provides you more overhead and a decreased max observable temp than a thermostat that opens at 19x* 

Of course you can run without a thermostat but then you might run into running / tuning issues where the engine does not get hot enough and make maximum safe, reliable power. Or you might run into issues where some of the coolant is diverted back into the engine instead of to the radiator.

In reply to RX8racer :

Couple of things- don't assume that colder is better. Some engines it is, and others run better over 200. 

edit- a long time ago GRM did an article on engine temp, and iirc, the engine they tested did better north of 200 due to oil issues  

Second, if you run at 220, it really won't matter much if the stat opens at 180 or 195. It may reach 220 a little faster with 195, but both will due to other factors. 

On my racecar I have two temp senders, one before and one after the radiator. It really helps narrow down issues and spot them before things go wrong.

In reply to RX8racer :

Keep in mind that modern engines are designed to run hotter so you need to be careful with how much you reduce the thermostat's opening temperature - you definitely don't want the engine's track temps to become lower than stock street temps.

BMW uses thermostats on some of their newer cars with an electric heating element in the wax so that the ECU can affect the thermostat's opening temperature to reduce temps on track.

Also note that it's possible to band-aid a weak/small radiator for track use with a lower-temperature or deleted thermostat, what happens is that instead of temperatures constantly climbing out of control the engine will overcool on high-speed sections which gives some thermal headroom for the lower-speed parts of the track.

In dyno sessions on my car we found almost 10% more power at 195-200F than we had at 180F. Very repeatable results. On a motor with 125hp that was a big jump.

In reply to alfadriver and GameboyRMH :

Mostly agree... but I'm actually not assuming colder is better. 

Optimal operating temps will depend on the engine and the tuning of the ECU.  I'm saying that you are potentially missing one of the controls of the cooling system if you are not addressing the temp at which the thermostat opens and sends all the coolant to the radiator.  My statement does assume that the operating temps are higher than desired and the goal is to lower your operating temps to a lower operating temp - which is usually the problem with track and race cars observed in the video and link.

On the Miatas, RX7s and RX8s that I am experienced with, ECU starts decreasing timing around 210* ish water temp.  So anyone trying to manage their cooling temps on track needs to learn what operating temps their engine is designed / programmed for.  1.6 Miatas seem to like 190-195 measured at the rear of the head for example - similar to what Trent observed on his car.

No idea what oil issues GRM might have experienced so can't comment on that. Obviously, the oil needs to get to operating temp as well.

In reply to RX8racer :

But a lower operating t-stat isn't going to change anything- it just opens earlier.  Eventually it will reach whatever peak temp it will reach.  Eventually both a cold and hot t-stat will be full open, and you are stuck at 220.  The only time a t-stat will matter is if you have a cooling system capable of cooling the engine to below the original t-stat opening.

As for your experience, it's totally correct for those cars.  Just perhaps not everything.  I would personally shoot for a floating temp in the 195-205 range for those cars.  I have worked on cars that didn't really need to retard spark until 215, and then not seriously until 220.

alfadriver said:

In reply to RX8racer :

But a lower operating t-stat isn't going to change anything- it just opens earlier.  Eventually it will reach whatever peak temp it will reach.  Eventually both a cold and hot t-stat will be full open, and you are stuck at 220. 

My experience forces me to disagree with this part of your statement.  Your statement might be applicable to some cars but not all cars.

Let's use the Miata as an example measuring coolant temps at the back of the head.  Koyo rad.  The engine coolant temps will gain about 10-15* of heat at race pace on an 80-90 ish degree ambient temp day.

If you start with a 180* thermostat, coolant temps will run at 190-195* over a 20-30 minute session

If you start with a stock 195* thermostat, coolant temps will run 200-205*.  I remember the temps would actually drift a bit higher to about a sustained 208* with the stock thermostat on longer sessions.

I tested with a 160* thermostat too.  Engine struggled to run at 180*.

So the operating temps maxed out at a lower overall temp by running a thermostat that opens earlier. 

YMMV of course but I would love to hear results from others testing this on their cars.  Seems logical that if you open the thermostat earlier, run the coolant through the heat exchanger sooner your results will be a lower overall operating temp seems correct.

Ian F (Forum Supporter) said:

NickD said:

I remember when Hot Rod Mag did the Hot Rod Rescue column and so many were overheating issues, and very frequently it was "Timing was too advanced". Timing actually effected a lot of stuff that you wouldn't necessarily think of.

A joke I've read in classic car circles are 90% of carburetor problems are ignition related. 

The joke is that it's closer to 99%.

RX8racer said:

alfadriver said:

In reply to RX8racer :

But a lower operating t-stat isn't going to change anything- it just opens earlier.  Eventually it will reach whatever peak temp it will reach.  Eventually both a cold and hot t-stat will be full open, and you are stuck at 220. 

My experience forces me to disagree with this part of your statement.  Your statement might be applicable to some cars but not all cars.

Let's use the Miata as an example measuring coolant temps at the back of the head.  Koyo rad.  The engine coolant temps will gain about 10-15* of heat at race pace on an 80-90 ish degree ambient temp day.

If you start with a 180* thermostat, coolant temps will run at 190-195* over a 20-30 minute session

If you start with a stock 195* thermostat, coolant temps will run 200-205*.  I remember the temps would actually drift a bit higher to about a sustained 208* with the stock thermostat on longer sessions.

I tested with a 160* thermostat too.  Engine struggled to run at 180*.

So the operating temps maxed out at a lower overall temp by running a thermostat that opens earlier. 

YMMV of course but I would love to hear results from others testing this on their cars.  Seems logical that if you open the thermostat earlier, run the coolant through the heat exchanger sooner your results will be a lower overall operating temp seems correct.

It sounds to me like in that specific use case, the engine is acting like a thermal sink, the radiator/cooling system unable to bring it down in real time, so you're just starting from a lower position.  If you ran it long enough they should find the same equilibrium....

Assuming that both thermostats had the same open area.  They might not.

In reply to RX8racer :

So that Miata had enough cooling capacity.  If running 220 with a 195 stat, a 180 stat isn't going to do that much.  It's a tool when the rest of the system is powerful enough to reject the heat.