'88 Comanche coolant reservoir cracking after 2nd replacement

[Classy Comanche]

Thank yall! I'll have the tank installed and the plastic overflow installed as well.

[watchamakalit]

I'm another proponent of the macs tank.  great product and easy to install. 

[PIKE]

Macs tank and 1987-1993 expansion bottle.

[Classy Comanche]

Thank you sir. So all I need is the Mac tank and the plastic overflow tank to hook onto said tank. The picture I posted below is a early to mid 2000's dodge durango upper radiator hose. I'll be visiting my mechanic soon. So as the list is its 

1. Mac's aluminum tank 

2. Plastic overflow catch reservoir 

 

And that's all I have. I feel like I purchased this hose yesterday out of sheer panic lol. And the aluminum tank does indeed have a outflow nipple like the plastic one does right? So the plastic one has a inflow of the side where it spits the coolant in said reservoir meanwhile there is another nipple/hole at the bottom of the tank that sucks the coolant out. Does it have a bottom outflow nipple?

[Eagle]

On 6/18/2022 at 12:41 AM, velco said:

You can run the Mac's tank as a closed system, just plug the overflow.

 

If you run it as a closed system, you can only fill it halfway. And then run a higher-pressure than standard radiator cap.

 

Coolant expands when it gets hot. Something has to accommodate that expansion, because fluids con't compress. In an open system, the radiator cap allows coolant to escape to the recovery tank when it expands, and then allows the system to pull the coolant back ("recover") as it cools down.

 

With a closed system, there is no spring-loaded radiator cap, and no recovery bottle for the expanded coolant to flow into. That's why the coolant bottle in the early 4.0 liter systems is only filled halfway when cold -- air can compress under pressure, so that air space allows for the coolant to expand by compressing the air in the plastic ooolant bottle. That's why it is so important to never over-fill that bottle.

[Eagle]

5 hours ago, PIKE said:

Macs tank and 1987-1993 expansion bottle.

 

Specifically, an 87-93 2.5L 4-cyl recover bottle -- and using it requires getting rid of the factory air filter box. Not everyone wants to do that.

[fiatslug87]

6 minutes ago, Eagle said:

Specifically, an 87-93 2.5L 4-cyl recover bottle -- and using it requires getting rid of the factory air filter box. Not everyone wants to do that.

Actually you can get both to fit, a little tight but doable.

[eaglescout526]

 

I mean, it is tight regardless, 2.5L & 4.0L share the same air box bottom, just not the lid.

[Classy Comanche]

Yeah I plan having my aluminum tank installed and the recovery tank installed as well. Only fill halfway correct? And the recovery tank should be empty or should that be filled about halfway?

[fiatslug87]

Fill the Mac’s tank all the way and add some to the overflow bottle.

[PIKE]

 

The overflow bottle has a min. and max. marks. Fill half way between them.

[Eagle]

2 hours ago, fiatslug87 said:

Fill the Mac’s tank all the way and add some to the overflow bottle.

 

What he said.

[Eagle]

41 minutes ago, PIKE said:

 

The overflow bottle has a min. and max. marks. Fill half way between them.

 

I would start by filling the overflow bottle to just above the MIN mark -- when cold. Check it when it reaches operating temperature. If it's at the FULL or MAX mark, you're done. If it's not anywhere near the MAX mark, add a bit more after it cools down.

[87MJJeep]

On 6/18/2022 at 7:55 PM, Pete M said:

if you add a cap that's a higher pressure than the closed system will see, it should stay a closed system.  I have a late model radiator (with a higher pressure cap) in my otherwise stock 88.   

I hate to hijack this thread, but...  I just converted to an open system with a late model radiator, and I have a 16 lb cap on the new radiator.  I ran a hose from the radiator neck's expansion port to the original closed system's reservoir.  So far coolant is not "expanding" to the reservoir.   I guess there is still enough air in the radiator to prevent coolant from traveling up the hose to the reservoir.  I've got the reservoir half filled and I have coolant in its hose.  

 

Until I saw your post, I wondered if the 16 lb cap was too high and I needed to swap to 13.  

 

[Pete M]

16 pounds is just fine.   

[87MJJeep]

19 hours ago, Pete M said:

16 pounds is just fine.   

 

Thanks!  

[pizzaman09]

I've had the exact same experience with the Rockauto tanks.  First one split at the seam and leaked all over my new distributor.  Replacement one had a leaky cap so I installed the non leaky original, that caused it to split at the seam on the driver's side.  I ended up using some high quality acrylic two part adhesive made by my employer to fix the cracked barbed fitting in the original circa 1990 tank.  It works great.

 

The Mac tank looks great, I will purchase one if the factory tank goes.

[dasbulliwagen]

I'm sorry I havent been on here much lately, but I'm the mechanic doing his work (classy comanche). I don't have a ton of experience on the 4.0 because my truck is the 2.5, but ive been on this site since 2008 and I was a Jeep dealership tech for 13 years. I'm not sure what the pressure bypass is in the stock syle expansion tanks cap, but  they never leaked from the cap, they just split at the seams. Hes been careful about running it too low on coolant thankfully. Today I installed the Macs tank, and an overflow bottle, using the supplied 16 PSI cap. The tank build quality seems really nice, and it went in with no issues. The overflow tank he bought was a generic one, and I put it right in front of the Macs tank using vac hose covered wire and a zip tie. This will work fine for now. We are trying to get him to the point of reliable drivability before tackling the other things it needs done.  

[fiatslug87]

Good to see you are still around and helping fellow MJers.

[dasbulliwagen]

1 hour ago, fiatslug87 said:

Good to see you are still around and helping fellow MJers.

 

I'm still in and out, just havent done much with my truck lately. Classy Comanche saw me sitting in my truck during lunch and stopped to talk. He hadnt had much luck working with the Jeep dealership, so I told him Id help . I can't work on anything at home, but he is able to bring it to my job at the Chevy dealer and I try to minimize the hourly rate time for things I'm doing for him. These stupid coolant bottles have been a real pain. It is a nice rust free original truck that just needs a little TLC. 

[Classy Comanche]

And oh my he's done fantastic work on my truck. Though I will ask about the Mac tank. When yall say "fill to the top" do you mean to the top of the ring? Or up to where the overflow nipple goes to the reserve tank? I'm just making sure where "full" is on this tank so I'm cautious and don't mess it up since these tanks are hard to see in moderately 

[fiatslug87]

[Classy Comanche]

Perfect! I'll fill it up to there

[Eagle]

12 hours ago, dasbulliwagen said:

I'm not sure what the pressure bypass is in the stock syle expansion tanks cap, but  they never leaked from the cap, they just split at the seams.

 

The OEM closed system coolant reservoirs are not "expansion" tanks, and there is no pressure bypass. See my explanation a few posts above. They are designed to be filled no more than halfway when cold, so when the coolant gets hot and expands, it has an air cushion above it to compress. That's what accommodates the expansion.

 

In an open system, the expanded coolant gets pushed out to the recovery bottle when hot, and it then gets sucked back into the radiator as it cools down.

 

Too often, people don't understand how this works, they overfill the reservoir, and that's what causes them to crack. Liquid doesn't compress -- air does.

[dasbulliwagen]

47 minutes ago, Eagle said:

 

The OEM closed system coolant reservoirs are not "expansion" tanks, and there is no pressure bypass. See my explanation a few posts above. They are designed to be filled no more than halfway when cold, so when the coolant gets hot and expands, it has an air cushion above it to compress. That's what accommodates the expansion.

 

In an open system, the expanded coolant gets pushed out to the recovery bottle when hot, and it then gets sucked back into the radiator as it cools down.

 

Too often, people don't understand how this works, they overfill the reservoir, and that's what causes them to crack. Liquid doesn't compress -- air does.

I'm assuming that the cap on the original style expansion tank has an overpressure release, though I could be wrong. That's what I was talking about. I know it's a closed sealed system. I just assumed there'd be some overpressure protection to keep from tank damage or blowing a hose off. That happened after one of the new tanks I put on his truck. It split open the weak point in the old lower radiator hose.