Piston Slap: Thoughts on custom cooling for custom vehicles?

[Hagerty]

I would appreciate your comments on dealing with engine cooling on non-factory built vehicles. Issues like grill openings, double core radiators, timing, additives, type of water pump, or other remedies. I have a couple of vehicles that I have struggled with cooling issues in the past, both running Chevy 350 small-blocks.
https://www.hagerty.com/media/maintenance-and-tech/piston-slap-thoughts-on-custom-cooling-for-custom...

[hyperv6]

Here is the cold hard truth on 90% of the over heating issues. Too many people have a undersized radiator.

Often many cars are running engines that have been modified. Most are running several hundred more HP than what they originally had. Yet people try to use a stock or original radiator.

More HP generates more heat and you need to account for it with more cooling. The Radiator is the prime place to do that. Most people just never have enough cooling capacity.

If you are lacking space use a radiator like a Becool as it has larger oval tubes that are more efficient for cooling.

Other mistakes. Not running a thermostat or restrictor. Too fast of flow will never let the coolant in the radiator long enough to cool down. You end up putting the hot coolant right back in the block.

Wring fans for applications. And not running shrouds for the fan kills their efficiency.

It kills me to see people spend tons of money on an engine but invest nothing in a Radiator. Then risking that investment with an old or undersized radiator.

On most Jeep’s it is all about the Radiator and making sure to shroud the fan. The openings are large enough and most fans will cool easily.

No need for fancy pumps or additives.

My neighbor has a CJ5 with a 400 hp Chevy and nothing fancy but a good radiator. No cooling issues. He also has a Willys Panel that has a 350 in it with air and all. It is tight but a good radiator and electric fan made it a cross country driver.

[Snailish]

Fan shroud is the missing tip from the article.

Making sure all the correct factory original pieces are in place on your stocker is one thing.

The second you change the engine, add pulleys or anything that moves the factory fan location to the shroud you have changed the function.
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Old school rodders added louvers, tossed the hoods sides and/or hood --form and function

[hyperv6]

When it comes to shrouds they must fit or be made to fit. You can move the fan on a spacer or you can get a new shroud and make it fit. 

lovers were used as back in the day they had little option as there were not many good efficient higher capacity radiators that would fit. Today there are so loungers are for show today most times.

you want to avoid lovers if you drive in weather as water on the engine is not a good thing. 

[Snailish]

A good louver job would be one of the most expensive ways to get a bit of cooling today anyways.

Also hard to reverse (without a spare body panel that you louvered).

[mx5_7]

Cool article!
*laughs at own pun*

This is a bit of a rabbit hole. Some serious and lengthy engineering discussion can be had. A little food for thought as I just went through this on a swap car this winter:

1. Cooling additives. While additives may be expensive and gimmicky, it is important to consider your antifreeze to water ratio. Ethylene glycol raises and lowers the phase transition points for water but also decreases it's specific heat capacity. Something to think about for your application.

2. Airflow and grill/hood openings. Your radiator needs a couple things to be able to reject heat effectively. Mainly capacity and time for both the water and the air. What surprised me, is that in most cases radiators can benefit from slower air. This means in an ideal setup you have a diffuser into the radiator and a nozzle out (approximately a 1/3 area ratio for both). It also benefits to try to ensure high pressure ambient air at the inlet and low pressure at the outlet (the Miata community has done a good job of mapping out pressures to determine the correct location for louvers, but there are general guidelines you can follow to find low pressure areas on any car).

Then there is fan shrouding and efficiency of fans... A whole additional conversation!

[Sajeev]

@hyperv6 @Snailish good point on the fan shroud. I added it to the list (and put it pretty high up there!)  Thank you very much! 

[hyperv6]

No problem. In my line of work this is a common issue and often on Jeeps with small blocks. 

[drm101]

The fan should be 1/2 way in and out of the shroud. Leave an inch or so between the fan and shroud. I prefer a good thermal clutch fan over an electric fan. If you want to run an electric fan, make sure the alternator, battery and wiring can handle the additional load. A fan capable of properly cooling a typical stock V8 will pull a ton of current.

[JeffWeimer]

A question about running a separate transmission cooler in series - should you run the fluid through the radiator cooler first and then the air-to-fluid cooler, or the other way around?

My guess is that if you're worried about transmission temperature, you should do the first; if not, then the second.

[Sajeev]

While I have never measured the ATF temperatures myself to see the difference, the general consensus is that you run the the fluid through the radiator first, then to the trans cooler. 

[BMD4800]

Correct, radiator first, then cooler. Unless you live in a really cold (arctic) climate and don’t perform plow work, then you’ll need a partial block off to keep it from getting under 100.

[MickeyB]

The change in the Water Pump solved the problem on the 1953 Kellison J4 Roadster. I eventually removed the ducting and returned the timing to the recommended settings. I also removed the twin electric push fans but left the double core radiator in place. By using a stock Chevy water pump the water was circulated at a slower pace allowing for more cooling time in the radiator.
I have not been as lucky with 350 small block in the CJ7. There is plenty of grill opening and changing the timing didn't help that much. the water pump appears to be stock Chevrolet so the next step will be to invest in a double core radiator.

[Sajeev]

I bet the radiator will fix it, if not the next step might involve addressing the fan and/or fan shroud. 

[gdelfium]

A radiator upgrade (3 or 4 row vs. 2 row) is an option. Also, an engine oil cooler, while expensive, would likely assist in cooling as well. The idea is to take heat out of the engine and this can be done via cooling the water or the oil. The old air-cooled Volkswagens and Porsches were air and oil cooled for example.

[Sajeev]

Another great idea. Thank you for sharing! 

[BMD4800]

Don’t forget the block.

Out here in Arizona, the water is hard and old blocks get filled with gunk and don’t cool well. As tempting as it is to use tap water, distilled is better.

Mx5_7 is spot on. Use the least amount of coolant needed for boil over and freeze protection. Make sure your cap builds pressure, or it will rapidly boil over and those steam pockets are bad voodoo.

[Oldroad1]

Bracket mount your cooling fan so that the fan housing is right up against the radiator's upper center core if your using a down flow. That way the fan housing becomes the shroud. Always wire fan power through a low temp relay ground sender bout 175 degrees F and 180 F T-Stat. That way the fan will turn on just before the T-Stat begins to open, cold engine. The fan will cycle and keep the water temps a steady 180-190F.

[DUB6]

Unless I missed it (amongst all of the excellent input from others), I spotted a comment that raised my antenna: @MickeyB mentions that the Jeep has a "stock Chevrolet" water pump.  Depending on age, total hours of run time, water and/or coolant condition , and just plain old quality of the part to begin with, water pumps (or at least the impellers) can wear and ever wear out.  This can mean that while they are still circulating water, they may not be doing it quickly enough to sufficiently keep the flow through the engine and radiator to give optimum cooling.  Flow rates can be tested (generally best done at a radiator shop).  Some pumps can be rebuilt.  If not, replacements are relatively inexpensive.  Probably best of all (from flow standpoint) is changing to an electric water pump.

[MickeyB]

Excellent point. When I dealt with the high running temps on my 1953 Kellison J4 roadster with a Chevy small block, changing the water pump to a stock Chevrolet unit solved the problem. I hadn’t considered that on the 1988 CJ7 also running a chevy small block might have an older unit with worn impellers. That is an easy and inexpensive fix to try.


Mickey Brown
773-339-2379