Our Trials and Errors With Improving a 4x4's Cooling System

Is it hot in here, or is the 14-Day Flattie nearby? Many of you will remember from just over a year ago that our 14-Day Flatfender project was launched into use with an overheating problem. We promised we’d sort it out and give you an update on it. In the past 14 months, we’ve done plenty of research, talked to several experts, and tried several “guaranteed” remedies. The result is reams of information on what worked and what didn’t, and a still too-warm Flatfender.

We hoped to knock 20-40 degrees Fahrenheit off of our 4x4’s operating temperature with one or two easy and inexpensive fixes. This search led us to try many items we’re confident you’ve heard about and always wondered how well they worked.

Where We Started

The 14-Day Flattie is equipped with a 385hp V-8, a small but efficient aluminum radiator, an electric fan, and a temperature gauge that prefers to reside above 220 degrees. The temperature gauge takes its readings from the front coolant passage in the intake manifold, just before the thermostat housing. Everything was working properly, but the Flattie would overheat gradually at slow speeds on the trail and quickly on blasts up sand dunes.

Our Suspicions

We believe that our small radiator (about 14x17 inches of core surface area) is a problem. We also feel that, by leaving the inner fenderwells intact, we trap hot air in the engine compartment. This theory was supported whenever we left the hood up when idling on the trail, and the temperature slowly came down. A larger radiator won’t fit without major work under the hood, and we’d like to avoid the cost of yet another custom radiator. We are also still unwilling to butcher the inner fenderwells. That leaves us in a position to try just about anything.

Our Testing

We took the Flattie to Johnson Valley, or Hell on Earth as we refer to it during the summer months. Ambient temperatures ranged between 95 and 105 degrees during our testing. We brought the engine to operating temperature, allowed the engine to idle for 10 minutes, drove to a sand dune area, did laps on the dunes, drove back to camp, and let the engine idle for another 10 minutes. We noted engine temperature at every point. The testing spanned three days and we monitored ambient temperature and humidity. The idling tests simulate sitting in traffic as well as on slow-moving trails. The drive to and from the sand dunes tested the cooling at part throttle with a little airflow caused by the vehicle moving in addition to the cooling fan. Climbing the sand dunes under power was the extreme cooling test—lots of horsepower under load builds lots of heat.

Conclusion

We still have some work to do. Most of our changes resulted in no real change. Our final configuration still leaves the Flatfender with marginal cooling on hot days. Although Evans Cooling says that the engine can operate at a higher temperature without causing damage with its NPG+ coolant, we just can’t stand seeing the temp gauge in excess of 240 degrees. And we can’t believe that this is good for aluminum heads on an iron block.

It’s very important that you realize that our testing presented some facts related to our application. We believe that our results would have been different if we didn’t have an underlying problem such as airflow through the engine compartment or a radiator that’s just too small. Our testing for next month’s issue will either confirm or refute these theories.

Concept: Mechanical fans cool better than electric.

Theory: Our worst overheating occurred on throttled drives up sand dunes. The mechanical fan should increase airflow through the radiator as engine speed increases.

What we did: We removed the 14-inch electric fan and fitted a 14-inch Flex-a-lite flex fan to the engine. These fans are designed to deliver maximum airflow at lower engine speeds, and the blades flatten slightly at higher speeds to minimize horsepower loss.

Cost: $30 for the stainless steel model we used.

What happened: The electric fan moves more air at slow engine speeds, so overheating at idle was a bigger problem with the mechanical fan. Cooling at higher engine speeds was not improved.

Theory: We’ve used Flex-a-lite’s 400 Series plastic fans before with great success. They’re popular with off-roaders because a sheet of metal screen over the radiator will cause the fan to break instead of destroying the radiator if contact occurs.

Cost: $15

What happened: The engine ran slightly hotter on the sand dunes, verifying that this fan cannot move as much air as the metal flex fan at higher engine speed.

Concept: Every mechanical fan should have a shroud.

Theory: Without a fan shroud, the fan will draw air from the source of least resistance—around the radiator instead of through it. The blades of the fan need to be half in and half out of the shroud to avoid just circulating the air inside the shroud.

What we did: Because everything is custom under the hood of the Jeep, we had to make our own shroud. At a local hardware store we picked up metal supplies and rubber insulation to create a shroud and seal it safely to the radiator.

Cost: $25

What happened: This had virtually no improvement compared to the previous test. This was our first confirmation that we aren’t able to move air through the engine compartment.

Concept: An inefficient water pump could be causing excessive cavitation.

Theory: Cavitation is the production of small vacuum pockets that disrupt fluid flow. These pockets of air greatly decrease the efficiency of the pump. It isn’t able to move as much water through the cooling system.

What we did: Replaced the aftermarket aluminum water pump with a new GNB water pump from AutoZone.

Cost: $35

What happened: There was no difference in any of our testing, indicating that excessive cavitation at the water pump was not a problem.

Concept: A lean air/fuel mixture will cause an engine to run hot.

Theory: An excessively lean air/fuel mixture causes an engine to run hot because of its high air content. Adding fuel to the mixture (making the mixture richer) should lower the operating temperature.

What we did: Our 385hp engine requires a fuel curve radically different than a stock engine. It needs more air and fuel at idle and in the part-throttle circuit as well as the deep-throttle circuit. This requires modifications beyond jets and metering rods, so we had JET Performance build a Stage 2 Q-Jet custom for our application.

Cost: $375

What happened: We had lots more power on the sand dunes—and we do mean lots. Lots more power means lots more heat. However, the engine ran cooler at all points except idle, where it ran the same temperature as before.

Concept: Water has better heat-transfer properties than antifreeze.

Theory: Because 100-percent water can transfer heat (the name of the game in engine cooling) better than antifreeze or a mixture of antifreeze and water, running all water in the cooling system should lower operating temps.

What we did: Drained all antifreeze from the radiator and the engine (small-block Chevys have a water-jacket drain plug on each side of the engine) and replaced it with 100 percent water.

Cost: Free

What happened: It ran cooler. There are two major drawbacks: 100 percent water promotes corrosion in iron and aluminum engine parts and will slowly destroy your engine and aluminum radiator. And water freezes, which will cause engine damage this winter, making the first drawback not as important.

Concept: Coolant isn’t staying in the radiator long enough to cool before returning to the engine.

Theory: Adding a restriction to the coolant flow path should keep coolant in the radiator longer, cooling it more. A thermostat will create this restriction. If the operating temperature lowers enough, the thermostat will close, holding the coolant in the radiator even longer, cooling it even more.

What we did: Installed a 180-degree thermostat from AutoZone.

Cost: $6

What happened: Operating temperatures increased at all test points. This told us that restricting flow was not beneficial and led us to believe that greater flow may be beneficial. The thermostat was removed for the remainder of the testing.

Concept: There are coolants better than typical antifreeze.

Theory: Antifreeze will keep your engine coolant from freezing in the winter, and it raises the boiling point of water. It doesn’t really do anything to improve heat transfer (remember, that’s the idea of a cooling system). Evans Cooling offers NPG and NPG+ non-aqueous propylene glycol products. We used NPG+ which has a freezing point of -40 degrees (compared to -30 degrees for 50/50 water/ethylene glycol antifreeze mixture) and a boiling point of 375 degrees (255 for a 50/50 mix of water/antifreeze). This higher boiling point means that there is liquid coolant around hot spots in the engine such as the exhaust valve areas in the heads. Water and 50/50 mixes of ethylene glycol–based coolants vaporize in these areas and lose their ability to transfer heat. The operating temperature will probably not decrease (in fact, it may increase slightly). The fact that there will be heat transferred from the hottest spots in the engine means the engine will escape damage up to 280 degrees. This coolant also has anticorrosion properties, and its lifetime is indefinite—you’ll never need to change it.

What we did: Completely drained the coolant and replaced it with Evans Cooling NPG+.

Cost: $22 per gallon, $66 for our application.

What happened: The operating temperature didn’t decrease, but the engine did run at a higher temperature without spitting coolant into the overflow. This seemed to confirm what Evans Cooling claims about its product.