Overheating from heat soak

[WSS]

Looking for some real world info on hemi's stuffed in JKU's. I am still having a heat soak or air flow problem. I have a Ron Davis radiator system with twin 12" spal fans, old style noisy ones. My issue is at highway speeds under load. As soon as I start a grade, the coolant temps rise to 230, when the grade is over (flat or downhill) the temps drop to 190. Trans temp never goes above 190, usually around 170. I am going to seal the bottom of the radiator for more forced air through the grill.

I have removed the inner fender liners for more flow, is this counter intuitive? Will this make the problem worse? Also, do hood louvers work in this situation?

I gotta get this fixed cause it is going to catch me one of these days.

 

[Cimmerian]

Did you do the install yourself or used a swap shop? You might want to contact one of hemi swap specialists like AEV about it if you haven't already.

 

[BLACKJKU]

Do you have one of those expensive hoods like I do with the vents in it? The cool air comes in and the heat will rise if it can vent out it could make a difference, otherwise your just blowing the heat around in there until it can try to get it pushed out.

 

[WSS]

I did not swap myself. It was done as a kit by "hemiswap.com" which is out of business now. The actual install was done out of a shop in Gilbert AZ, as best I can tell. It was done in 2009 for the 2010 sema show by the owner of discount tire. I don't think it was offroaded much until I got it as the third owner. I have found all the weak spots like the overheating. the Jeep has 68k on it and the swap was done at 28k (along with all the undercarriage and bling).

I do have one of those "expensive hoods" but it lacks any useful vents. It has a "cowl induction" type setup but the hemi runs a K&N type, so the cowl system is not used. It is a "GR8tops" brand as far as I can find.

 

[BLACKJKU]

I did not swap myself. It was done as a kit by "hemiswap.com" which is out of business now. The actual install was done out of a shop in Gilbert AZ, as best I can tell. It was done in 2009 for the 2010 sema show by the owner of discount tire. I don't think it was offroaded much until I got it as the third owner. I have found all the weak spots like the overheating. the Jeep has 68k on it and the swap was done at 28k (along with all the undercarriage and bling).

I do have one of those "expensive hoods" but it lacks any useful vents. It has a "cowl induction" type setup but the hemi runs a K&N type, so the cowl system is not used. It is a "GR8tops" brand as far as I can find.

View attachment 131030

My hood has vents in the top on each side of the center.

 

[WSS]

I installed a pair of spiked louvers (blemished) on the hood. It worked. Dropped the temps on the same run/climb and speed 9 degrees. They look good. I could not find the blemishes. Maybe the driver side louver was bent the wrong way, meaning the dross or down side of the cut is up, it’s a little sharper than the passenger side.

I have the advantage of having the “cajon pass” close by. I can test on it and do a round trip in about 45 minutes. It has varying grades with the steep part at the end.

I can actually feel the heat rising out the vents. In fact, my side vents work better too after the new install. I have a thermal monocular and it shows a steady stream of hot air flowing through the louvers when the fans start.

 

[BLACKJKU]

I installed a pair of spiked louvers (blemished) on the hood. It worked. Dropped the temps on the same run/climb and speed 9 degrees. They look good. I could not find the blemishes. Maybe the driver side louver was bent the wrong way, meaning the dross or down side of the cut is up, it’s a little sharper than the passenger side.

I have the advantage of having the “cajon pass” close by. I can test on it and do a round trip in about 45 minutes. It has varying grades with the steep part at the end.

I can actually feel the heat rising out the vents. In fact, my side vents work better too after the new install. I have a thermal monocular and it shows a steady stream of hot air flowing through the louvers when the fans start.

View attachment 131036

View attachment 131037

It was a good thing I thought about that, it seems like there was a Post many years ago about a similar issue.

 

[pc1p]

I was going to say that in stock form, most 5.7's will hit 230° underload. The only real way to shed heat is to change fan size, change the fan logic, and/or ventilate the engine bay (sometimes with limited success on that last one). That dual-fan Spal looks to be good for 1800 CFM, which puts it only slightly under what most assume what the Pentastar JKU fan does (there's no official rating on it, but most suggest near 2000 CFM max). Assuming you are getting proper airflow through the radiator, I'd be looking at your fan logic.

I am guessing that Dakota Customs were running the PWM signal off of the TIPM similar to the old AEV swaps. This works, but you're limited to TIPM/ECM limitations. You might want to also consider something like the RPM Extreme (or similar) controller, which will have much better fan logic than what the limits of the ECM programming are. Alternatively, depending on your space, the popular "Camaro" fan with appropriate PWM controller will basically cool down a nuclear explosion.

Seems like the vents helped, so that's good. Sometimes they help, sometimes they don't, and sometimes they hurt. It seems that smaller vents can help with the "air dam" effect at speed and can help move air through the grille/radiator instead of around it.

BTW, do you know the shop in Gilbert? I know a few shops from my time out there... I can potentially put you in contact with the builder if you need to ask some questions and they're not available anymore.

 

[WSS]

I was going to say that in stock form, most 5.7's will hit 230° underload. The only real way to shed heat is to change fan size, change the fan logic, and/or ventilate the engine bay (sometimes with limited success on that last one). That dual-fan Spal looks to be good for 1800 CFM, which puts it only slightly under what most assume what the Pentastar JKU fan does (there's no official rating on it, but most suggest near 2000 CFM max). Assuming you are getting proper airflow through the radiator, I'd be looking at your fan logic.

I am guessing that Dakota Customs were running the PWM signal off of the TIPM similar to the old AEV swaps. This works, but you're limited to TIPM/ECM limitations. You might want to also consider something like the RPM Extreme (or similar) controller, which will have much better fan logic than what the limits of the ECM programming are. Alternatively, depending on your space, the popular "Camaro" fan with appropriate PWM controller will basically cool down a nuclear explosion.

Seems like the vents helped, so that's good. Sometimes they help, sometimes they don't, and sometimes they hurt. It seems that smaller vents can help with the "air dam" effect at speed and can help move air through the grille/radiator instead of around it.

BTW, do you know the shop in Gilbert? I know a few shops from my time out there... I can potentially put you in contact with the builder if you need to ask some questions and they're not available anymore.

Is 230° too hot? I have hit 235° once and then brought it down as fast as I could, which is easy, just get off the gas basically. My fans are dual 12" brushed ( and really noisy). When I bought the JK, it was wired to run full speed at all times. I got tired of screaming over the sound when getting spotted lol. I put in a derale pwm, it is super basic and really has no control. I do suspect the fans create some sort of block at highway speeds. It never gets above 210° on the trail, even in the summer. The vents seem to have broken that block. Another thing I added a couple days ago (before the louver vents) was a piece of kydex plastic below the radiator and front bumper, this "completed" the funnel, so no air could be deflected at speed. This helped quite a bit too. SO, I am getting there but slow.

On the subject of fans and logic, Are the brushless fans that produce 2k cfm real? I could fit two 12" fans easily almost drop in to replace my 12" spal's. Are they quieter? How is logic controlled, I understand that I cannot use a pwm like my derale to control brushless fans.

I am not sure of the shop in Gilbert, I do know they must have been a really good shop. They did a rotiserie on the tub/body and a frame off undercarriage build. All color matched. It was genright's poster child for a few months. The bottom is entirely Teraflex too.

 

[pc1p]

Is 230° too hot? I have hit 235° once and then brought it down as fast as I could, which is easy, just get off the gas basically.

Depends on who you ask and what you're referring to (i.e. oil temp or engine temp)... modern engines and modern lubricants are designed to run hotter (the 3.6L is a perfect example of this) for better efficiency due to higher cylinder pressures and overall better vaporization of the fuel mixture. Where people can get "uncomfortable" is when you start pushing the higher limits of what WAS considered "normal" from decades ago.

The old notion that "240° (oil temp) kills oil" was true back when the YJ was cool and the TJ was new, but that's not so applicable to modern times. Back when a typical engine temp was ~198-203°, one would estimate oil temp to be roughly +10-20°. Under high loads, oil could peak near 240°, which indeed did cause degradation, drastically decreasing oil life and lubricity in some instances.

Nowadays, modern synthetic oils can withstand 240° essentially indefinitely, and engines running at 240-245° are typical, with essentially zero viscosity or oxidative issues. Above 260° and you'll certainly see accelerated degradation of oils, but with sufficient oil change intervals, this isn't really an issue outside of constant, abusive environments.

My fans are dual 12" brushed ( and really noisy).

Are you still running the brushed fans?

When I bought the JK, it was wired to run full speed at all times. I got tired of screaming over the sound when getting spotted lol. I put in a derale pwm, it is super basic and really has no control. I do suspect the fans create some sort of block at highway speeds. It never gets above 210° on the trail, even in the summer. The vents seem to have broken that block. Another thing I added a couple days ago (before the louver vents) was a piece of kydex plastic below the radiator and front bumper, this "completed" the funnel, so no air could be deflected at speed. This helped quite a bit too. SO, I am getting there but slow.

Since your temps weren't really under what I would consider HEAVY load (highway cruising is generally light to moderate load, though higher with bigger tires and lift due to aerodynamic drag) - AND you seem to keep cool on the trails, you are likely dealing with an airflow/air dam issue (which the vents seem to have helped!). Adding that Kydex below the radiator showing a positive benefit is also evidence that this is an air dam issue (damn it!! couldn't resist )

On the subject of fans and logic, Are the brushless fans that produce 2k cfm real? I could fit two 12" fans easily almost drop in to replace my 12" spal's. Are they quieter? How is logic controlled, I understand that I cannot use a pwm like my derale to control brushless fans.

The OEM GM Camaro fan is rated at ~2200 CFM. The Pentastar JK 3.6L OEM fan is commonly assumed to be ~1900-2000 CFM. The JL Fan (850W motor I believe, drawing nearly 60 amps at 100%) is comparable to the Camaro fan (though not as skinny). These are all brushless and Pulse-Width Modulated ("PWM", for those who may not know what that means). I'm not familiar with the Derale unit, but the old AEV, Novak, etc. are all capable of controlling any PWM-signal input.

From a numbers perspective, two 12" fans covers the same amount of surface area as a single 17" fan, though there are many advantages of having a large, single air flow "path" through the center of the radiator core, vs two small paths. A larger, single fan blade results in better static pressure (which is actually what "pulls" air through the radiator and is arguably more important that absolute "CFM" ratings), less noise, and less turbulence at the front of the grille area. There's also the potential of additional air damming due to the fan shroud...

I am not sure of the shop in Gilbert, I do know they must have been a really good shop. They did a rotiserie on the tub/body and a frame off undercarriage build. All color matched. It was genright's poster child for a few months. The bottom is entirely Teraflex too.

View attachment 131044

That is sweet! I wonder if that is something built by Don (from RPM Steering), as he was an earlier adopter of the Hemi in JK's (as opposed to LS swaps)...