maximize 360 summer coooling

[rang-a-stang]

I also just submitted the following to Stant:

Hello Stant,

I own a 1979 Jeep Cherokee Chief with an 1978 AMC 401 in it. It is bone stock. There is a debate on my full size Jeep forum discussing if a rig will overheat or never heat up if a the engine is run without a thermostat. The two sides of the debate say:
1) No TStat and the rig will overheat because coolant flows through the radiator too quickly to exchange enough heat with the air.
2) No TStat and too much coolant goes through the radiator and it will over cool and never reach operating temperature.
Is there truth to either or both of these statements? If so, which one/how? No one is saying an owner should run w/o a TStat, we are just debating what the results would be if we did. We are not looking for a specific Jeep/AMC/V8/Carb answer, we are just hoping for a general answer. Something like:
"Generally speaking, most water cooled, gasoline engines will __________ if operated with no TStat is installed when one was originally designed to be installed. This is because __________."

Anything you guys can offer to us? We are on the International Full Size Jeep Association Forum. Let me know if you want the link and I can send it to you.

[SJTD]

The problem with this equation:

Q = WC Dt where W = flow rate of fluid (lb/hr) C = specific heat of fluid (Btu/lb/degrees F) Dt = temperature change of the fluid (degrees F)

Is that there are two unknowns. Delta T and Q. The conclusion stated assumes dT remains the same between the two conditions. If it does and flow increases then yes, the heat transfer increases.

But if you increase flow the dt will change. This is the argument made above, that decreasing flow causes the water leaving the radiator to be cooler. True but only half of what goes on.

Have to go deeper and look at what's happening inside the engine and radiator at the metal/water interfaces. It involves more complicated equations involving the Reynolds number which is basically a measure of turbulence. Higher flow increases the Re giving better heat transfer at the metal/water interface.

I suppose I'll have to get out my old Heat Transfer book. Haven't used this stuff in years.

Seems to me I wrote up something on this including equations a few years ago but I don't know if/where I posted it.


Can we talk about back pressure helping low end power now?

[440sixpack]

More flow = more cooling. there is a point where more flow won't gain you anything but there is no point where more flow reduces cooling.

The only thing running with no thermostat gains is if you start with a lower temperature it takes longer to heat up. sort of like a loaded truck hitting a long hill with a run, it takes longer to slow down but you're still going to top the hill at the same speed.

[SJTD]

For doubters I will sell them a new water pump I've designed. Pumps less water.

I call it the Slo-Cooler.

[Herk]

If I remember right from Thermodynamics, the way a system pretty much dependent on surface area getting hot compared to surface area of heat rejection, and the velocity of the liquid (water) coolant really doesn't matter unless it's going way to slow (has to be moving fast enough that it doesn't boil and form air bubbles on the hot side). So long as the radiator flows coolant well, and air can move over it, a stock FSJ cooling system should work just fine.


Some new thermostats have pretty small holes in them. Small enough to be a restriction on a large engine. I've had good luck with this thermostat in any engine I've put it in: https://www.rockauto.com/en/moreinfo...179514&jsn=395

[rang-a-stang]

From Stant:

From my experience this will not over heat. If it is a cold day you will not build any heat in the cab of the vehicle. I use to pull the thermostats out when I was in my trail rig to avoid overheating. Not having a thermostat in will not allow the system to recirculate like it is designed. I hope this helps some. I also like running an 160 degree thermostat in my street/ strip trucks and cars. It would be just fine in a trail rig also especially if you are riding in the cold.

My thoughts on the response: He has personal experience running around w/o a TStat and did not overheat. In fact, he mentions running cold. hhhmmm....

[rang-a-stang]

From Stant:

From my experience this will not over heat. If it is a cold day you will not build any heat in the cab of the vehicle. I use to pull the thermostats out when I was in my trail rig to avoid overheating. Not having a thermostat in will not allow the system to recirculate like it is designed. I hope this helps some. I also like running an 160 degree thermostat in my street/ strip trucks and cars. It would be just fine in a trail rig also especially if you are riding in the cold.

My thoughts on the response: He has personal experience running around w/o a TStat and did not overheat. In fact, he mentions running cold. hhhmmm....

[SJTD]

160 Degree?

If and I do mean IF, a 160 degree thermostat would make the engine run cooler in hot weather it would keep the engine from properly warming up which is not a good thing.

All it would really do is open a little sooner. Wouldn't have any effect on steady state engine temp.

Amazing that you got that response from a thermostat manufacturer.

[Heavy_Metal_Thunder_81]

Just my .02¢

I've been running a 195° stat with a 100% stock cooling system in my Cherokee since I bought it over 10 years ago. Since then I've lived in Illinois, Florida, Virginia, Washington state, and the vast deserts of California. My rig has seen temps well below 0° and well above 110°, on highway, in city traffic, and flogged off-road...never once have I had an issue with the cooling/heating system. If your engine is mostly stock-ish and your stock cooling system can't keep up, then something is wrong with your system. Any type of trick or bandaid, is just that. There is no reason the factory system shouldn't be able to keep up. The factory didn't build vehicles designed to overheat. Just a thought.

[babywag]

x2 John, never had an issue either...

Far as this...
From Stant:

From my experience this will not over heat. If it is a cold day you will not build any heat in the cab of the vehicle. I use to pull the thermostats out when I was in my trail rig to avoid overheating. Not having a thermostat in will not allow the system to recirculate like it is designed. I hope this helps some. I also like running an 160 degree thermostat in my street/ strip trucks and cars. It would be just fine in a trail rig also especially if you are riding in the cold.

The way it is worded implies a reply from avg. Joe tech support and not an engineer. No different than some opinions I’ve read online.
There is really very little benefit in running a cooler tstat in a driver.
In a track only or race car that gets pushed hard and see lots of WOT it has been shown to help.

[rang-a-stang]

I totally agree with both of you. The only thing he really provided was first hand experience of running w/o a TStat.

[letank]

I got a decent price for a alum and plastic direct fit replacement at $182. My junk Copper and Brass scrap price may surprise me. Old Tranny line fittings fit new bottom tank.
Back on the Road Again. I love cruising in this last of the big Cherokees

Good news to report about the weekend show, I hope, so no more cooling issues...
May be a link for that direct fit $182 radiator ...


Thank you

[Probesport]

I got an all aluminum, welded one off of eBay for $120, my brass one is in good shape but I couldn't pass that deal up. Looks like the cheapest price going is $130 now.

That and the Contour fans should be golden.

[newtojeeps]

I bought one of those 160.00 aluminum radiators off the bay and the neck stuck up to high and so did the tank. I placed it in the top most holes while putting it in. I cannot lower it unless I drill new holes in the mounting flange.

[Probesport]

My aluminum eBay radiator for $130 was a perfect fit for my '88 waggy, only hangups were the overflow on the opposite side, and the trans cooler fittings being smaller, both of which are easily addressed.

Also a great fit with the contour fans.

I painted the top tank black so it looks a bit more appropriate.