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Keeping the engine cool

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  • Keeping the engine cool

    I only have 300 miles on the R2.8 swap in my Jeep TJ and I have already formed some opinions. First, I love the way it drives! The only negative thing I have right now is that the engine runs hot! Granted we are in the middle of summer and temps are in 90's, but I am finding that I can't run highway speeds without coming close to the overheat mark. Yesterday I took a buddy and we ventured to the top of the Big Horn Mountains. We left at around 8:00 AM and it was about 70 degrees, 40 miles of highway driving on two lane roads with speed held at around 62 mph and 2200 rpms and the temperature was holding about 200 degrees, not bad. Got to the base of the mountain and started the 15 mile climb up, all up, no breaks, 10-15%, 2nd gear 2500 rpms and the temp kept crawling higher and higher until I hit 220 and the amber light on the murphy gauge lit up for what I thought was over temp, but it turned out to be a fault code for the EGR. I pulled over and let the engine idle for about 10 minutes and it got back down to around 185 and I took off again, temp started immediately climbing again, so I dropped to 1st gear and about 2000 rpms. Maybe this grade is a little more that 15%, who knows. When I got to the top of the climb, I was at 9300 ft and then it was mixed driving up and down and then the trail got a little steeper and it was time for 4 low. By now, the load on the engine was low and the electric fan was keeping up just fine, engine temp down to 180 and it stayed there all day while driving some pretty cool Jeep trails, but the temp was probably around 65 degrees. When it was time to head for home, all was well until we got into the valley. The temp was in the upper 90's and if I tried to hold 62 mph the temp was 214 and climbing up to 217, slowed to 55 mph and it held at 214. So, I need some more cooling! I don't think the 16 inch fan I bought that was rated at 3000 cfm is even close to this. I read lots of reviews on different fans and I have decided to order the mechanical fan adapters from Quick Draw and run my stock mechanical fan with the new fan clutch from my 4.0. The electric fan is pulling air across the radiator very well as it has a nice aluminum shroud, but I don't think it has enough volume to keep the engine cool under a load. The radiator I am using is a new last year Frostbite aluminum thick 3 core that I bought from summit racing and along with a new fan clutch it solved the same issues of overheating I was having with the 4.0 gasser.
    Last edited by nuffsaid; 07-25-2022, 01:11 AM.

  • #2
    I would say this is not normal behavior for the R2.8. Unless I'm pushing mine over 2000 rpm and 80% load for sustain periods of time, It won't rise above 175°F or cycle the electric fan.

    First, lets start by having you post pictures of your cooling system. Radiator, fan, plumbing and airflow pathways in front and behind the radiator. Please include pictures of the de-aeration plumbing. This is will a good starting point to diagnose your issue.


    • #3


      • #4
        Driving around at low speed, 4 low at 9-10000 feet elevation and 65 degrees, engine ran mostly 180 degrees. Working the engine climbing pretty steep grade, 1st and 2nd gear, 8-15 mph engine got hot, electric fan was working. Driving home mid 90's 2200-2300 rpms, 60-62 mph engine knocking on the door of 220F, if I slowed to 50-55 and 2000 rpms temp would drop to about 214F. I have two temp gauges, the intellitronix gauge and the cummins gauge on the murphy. The intellitronix runs about 10 degrees hotter than the cummins gauge once it gets above 180F, up to that point they are pretty close. When the murphy gauge was reading 219F, the intellitronix gauge was reading 229. Feeling in front of radiator with fan running I can feel the air movement, feeling air coming out from fan, the air is hot, but not what I would say a lot of flow. Definately nowhere near 3000 cfm as advertised. My murphy gauge shows 24% load at idle, is this normal or do I need to do a throttle position recalibration? I never looked to see what percent of throttle was being used running down the road at 60+ mph, but it felt like I had a bit more to go and the engine response is very good. All of the highway numbers are in 5th gear as that is where she likes to run. I also would like to add that my radiator is a Frostbite 3 row aluminum with a 2.25 inch core and it really helped cool my 4.0 gasser that had cooling issues pulling the same grades after I also added a new clutch fan with the aluminum radiator.
        Last edited by nuffsaid; 07-23-2022, 09:55 PM.


        • #5
          Only glaring thing I see is the winch, bumper and lightbar disrupting airflow to the radiator.

          One thing to consider is your CAC is stacked in front of the radiator and that raises the static pressure required to pass air through both units. For the fan, this reduces its CFM. (keep in mind fans are typically rated at 0 static pressure and CFM drops quick as pressure increases) Also, the CAC heats the air prior to it passing through the radiator, so comparing its performance to the gas engine is a bit of apples to oranges.

          24% load at idle sounds normal. Mine is 23% typically. At 2500 rpm and 75 mph, I'm at ~70% load

          You could experiment by removing the winch and lightbar to improve airflow.


          • #6
            I am going to install the mechanical fan, hopefully tomorrow if fed ex drops off the adapter. I do have one area that needs to be fixed in front of the radiator though, there is an open area behind the grill in front of the radiator that needs a baffle to keep air from going under the radiator. That will also be on my list. I also removed the rubber inner fender shrouds because I think they hold in too much heat in the engine compartment. I will report back.


            • #7
              I just got done installing the mechanical fan from my 4.0 gasser. It had a new fan clutch that only had about 500 miles on it. I was able to reuse the factory shroud by turning it upside down, it is a little tight on the driver side, but I haven't heard it rub at all. I took it out for a test drive and watched my engine load on the murphy gauge and I am cruising between 65-70 percent at 62-65 mph. It is probably 90 degrees out and I ran about 7 miles up the highway and back. Engine temp stabilized at about 183-185 under load, with the electric fan I would have been at 205+. If my throttle input drops a little, so does the coolant temp. I have to say this is awesome! I used the quickdraw brand fan adapter, it is nicely machined and I used it at 2 inches thick, which keeps the fan clutch about 2 inches away from the radiator core and half of the fan is outside of the shroud. I have never had good luck with electric fans in the past and I will stick with what I know, mechanical fans work better in high load applications.