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Discussion Starter · #1 · (Edited)
2021 HO. - 2018 Fleece Coolant Bypass Kit

Wondering if anyone has installed a fleece coolant bypass?

I have one and started to install it and there is a bracket on back of the engine block to the flywheel housing. I think its blocking where the bypass would go. I'm worried about taking it off because it looks to be structural brace to help reduce stress from engine torque. I think the freeze plug is behind this brace. Blue tape is covering exhaust ports on the head, for orientation.


Update:

I pondered the direction of coolant flow though the motor and how the 2 thermostats (engine and bypass) interact with each other. The fleece opens at 180* which is before the main. This causes coolant to flow out the rear of the block, through the fleece, while the engine t-stat (main) is still closed at the front of the engine. Looking at how all this works, it would be really silly to run this fleece without a t-stat. It would probably cause the engine to run very cool and will not allow the main t-stat to perform its job. Also, I tried putting the t-stat on the topside of the fleece spacer for the main. You can't do it, it doesn't fit i tried, and I don't see why one would want to after looking at everything. There is a thick bracket I had to remove on the back of the block. It has 4 bolts and is definitely a structural support, which I am not sure how I feel about removing at the moment. But I did, and it was easy to get out. For the Aisin guys, the freeze plug is easy to remove with the correct tool. Get a piece of 1/8"x1" steel flat bar about 50" long. Sharpen one end with a grinder, not to a sharp point, but to about 1/4" wide at the tip. Set it at about 10 o-clock on the plug and tap it a few times with a hammer, super easy if you use this flat bar.

Hope this helps someone in the future.
 

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Discussion Starter · #5 ·
Thanks Hemi. They don't say anything about the support brace. I have to believe the plug is under that, but I am wondering why that support brace is there? I have never seen a cummins with it. I don't want to sacrifice structural integrity for this coolant bypass.

Anyone ever removed this support and left it off?
 

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You need to call up Fleece to see what they say as their instructions don't mention the brace. Honestly though for some perspective you should know that for decades people have been modifying the '07.0 and earlier trucks with more power than these new trucks make and no bracing on the top or side of the adapter plate was in place factory nor have I ever heard of it being done or referenced by the do-it-yourself or aftermarket offerings. Although I would say it was done due to the power levels and weight capabilities for hauling.
 

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Discussion Starter · #7 ·
Thanks Marq92. Ya I have installed these on all my cummins and never ran into this before.

Can anyone confirm if the standard output cummins has this brace?

Wondering if fleece made their instructions based off an SO truck.
 

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The SO trucks have them as well.
 

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They're also on 4th gens.
 

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Yeah I don't know it makes no sense to me.
 

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The 19+ kit comes with a bit more stuff you can see in the pictures.

The bracket comes off, don't worry about support. The bell housing/adapter plate bolts are plenty support.

Your most difficult task will be the rear freeeze plug. Most success ive heard comes from tapping an edgee loose with a long pry bar from under/behind the bell housing and then grabbing an edge with pliers once it is turned/exposed enough.

I will tell you after having 2 5.9s with this and 1 6.7 (current) that thermostate insidee rear piece is a 180 degree so your truck will run cooler which I personally do not like. IMO the truck runs too cool for unloaded operation. However I do think it is very useful and helpful for frequent loadeed use. I almost exclusively use the current truck for 5th wheel towing so im happy i installed it but if most of my operation was unloaded or daily driving i would not reinstall this and i live in southern AZ where its hot so likely even worse/cooler operating temps in most of the country.

I dont have any data showing that operating temp at 185 is worse than operating temp of 200 so maybe im 100% wrong and it could even help longevity to be that cool (185). I just thought id meention it because its something i noticed. You can also restrict airflow to rad to help juice the coolant teemp.

sorry bad typing, 1 hand brokee.
 

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Discussion Starter · #14 ·
Thanks for the info mb. Wonder if you could put a hotter t-stat in the bypass?

I called fleece and they said remove the bracket. Said those have been on cummins for the last 10 years. I'll post a picture of the bracket once I get it off just for curiosity reasons. Thanks everyone for your help.
 

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When I build a motor for my truck I want to run a Fleece coolant bypass but I would install the stock thermostat on top of the spacer so you can leave the rear housing without a thermostat just to keep things simple. Just had my thermostat fail, luckily in the open position, but it seems overly complicated to put another thermostat way in the back.
 

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The way they explain in the instructions is from bottom to top t-stat, spacer block, then t-stat housing. If you did that you wouldn't need the t-stat in the back of the block where the freeze plug was pulled and replaced with the bypass.
 

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Thinking of this mod for my '21 as well. Think it would be OK to remove the thermostat from inside the Fleece bypass? Reason being, I just see it as another moving part that could stick/fail.

That bracket is nothing new. Curious to see installed pics and what else you're doing. Looks like a fun build.
 
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