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Discussion Starter · #1 · (Edited)
I stumbled on this information by accident when I was searching for the next thing to replace that could possibly be causing my overheating problem with my 2000 wrangler tj 4.0. I had replaced the head gasket, water pump, fan clutch, thermostat, bypassed the heater core(turned out to be ok), so far. I called a local performance shop, that I found out sold the aluminum radiator which I had planned to put in my jeep. It was going to cost $700. After talking with the sales person for almost 45 minutes he believed from all the answers he'd received from me that I had an airlock somewhere in the motor. He said 4.0 engines are well known for airlock problems, and that he wanted me to come in and have them use a special vacuum tool to take a vacuum on the coolant system and draw a vacuum on the empty coolant system, check to make sure it had no leaks and then to refill the system, using the vacuum to pull the coolant back into the system. This was explained to me, it would eliminate air being put back into the system there by eliminating airlock problems which will cause hot spots. I did some research on google and found out the tool was available on amazon. So I purchased it and did the recommended procedure drawing a 30" vacuum, letting it hold the vacuum for some 20 minutes to ensure no leaks and then drew the coolant back into the system until it equalized to 0". Took the jeep out, for a test drive. Drove it all day with A/C on. No overheating at all....Temp on handheld scanner never went over 214 degrees, at idle. When running at highway and normal around town speeds the water temp. was 203 degrees. This was possible for me to share because I found an honest person in sales, who could have just as easily sold me a another part, a $700 part. But instead he did the right thing and offered a fix solution. I live in Charleston,S.C. and feel they should be recognized for their honesty and concern to try to get to the bottom a problem without concern for the financial gain. They are a Mopar performance provider named "Bouchillon Performance". I hope this helps others plagued with overheating issues that have replaced every item in the cooling system to no avail. :thumb:
 

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that is weird,I never heard of anything like that..do you have anymore details?? is this a normal occurance and if so,for which engines ??
 

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Lots of your newer engines have to be done that way.
I have been doing it for about 10 years.
It's the best way to fill it.

And when it's full, your done, just put the cap on.

Just be sure you have water And antifreeze ready, it fills up fast.

I put my water and coolant in a 5 gallon bucket and suck it out from there.

Back in the day we stuck a aspirin in the thermostat to hold it open.
 

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is there a way to get it full without buying this vacuum tool or disassembling anything ?? does this always happen or is it just with some ??
 

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I am very glad you were able to find help in resolving your overheating issue. I have had this issue when swapping engines or other major work and it is usually resolved with bleeding the system.

Here is where i disagree, as a small business owner competing with online retailers is a daily problem. This guy was nice enough to spend 45 minutes of his time helping you out (at no charge) this is time that cost him money in one way or another. And then you jump online and use his free advice to find what you needed. You might as well have slapped him in the face when he finished helping you.

Small business lives by helping customers with issues, its called customer service. This is something you cannot get from an online retailer with no real experience with actually fixing anything.

I recently purchased a BDS lift and I could of saved myself $50 with an online purchase. Instead I purchased from a local shop that specializes in four wheel drive that took some time to fill me in with little details about the product and issues I may encounter with the install. That was worth the $50.

The guy that helped you saved you $670!!! And people wonder why small business' are having a hard time in todays economy.

Ok rant over move.....
 

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is there a way to get it full without buying this vacuum tool...??
Sure. Just remove the heater hose from the thermostat housing while you are filling. That will vent the air as the coolant level rises. Any remaining air will be vented through the overflow when the vehicle is driven.
 

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Here is where i disagree, as a small business owner competing with online retailers is a daily problem. This guy was nice enough to spend 45 minutes of his time helping you out (at no charge) this is time that cost him money in one way or another.
It's called free enterprise for a reason.

Small business lives by helping customers with issues, its called customer service.
Customer service is one thing. Educating the customer at no charge, to the point that he no longer needs your service, is another matter.
 

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Sure. Just remove the heater hose from the thermostat housing while you are filling. That will vent the air as the coolant level rises. Any remaining air will be vented through the overflow when the vehicle is driven.
I replaced the water pump on my 97 a couple weeks back and refilled with coolant just like I always have..it is doing fine..yesterday,I flushed the radiator and refilled my 91 just as I always have and it seems to be fine...so,is this just a sometimes problem or what ??
 

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tangofox007 said:
Sure. Just remove the heater hose from the thermostat housing while you are filling. That will vent the air as the coolant level rises. Any remaining air will be vented through the overflow when the vehicle is driven.
^^^^^this^^^^^X2
 

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harleydragon said:
I did not remove anything on either of mine and had no problem...my question is why I had no problem but some do ??
Most of the the time when you open the cooling system on a 4.0, they get an air lock. It's not a big deal if you know this before hand, and I've always pulled the highest heater hose until it starts circulating, then close it up and watch the temp, and I've always used a heat gun to check for cold spots in the system before letting the customer take it. I've seen these engines (the Cherokees are much worse) run for 30 minutes or more, no problems, and develop an air lock when the customer drives away. Usually, it doesn't require a hose removal, just slide a screwdriver between the hose and pipe to let out the air, make sure it circulates, then tighten the clamp.
 

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I replaced the water pump on my 97 a couple weeks back and refilled with coolant just like I always have..it is doing fine..yesterday,I flushed the radiator and refilled my 91 just as I always have and it seems to be fine...so,is this just a sometimes problem or what ??
The problem occurs when air gets trapped in the head, behind the thermostat. A dry thermostat won't open as it should, and an overtemp condition results. If you are not having that problem, it could be that your thermostat is not sealing as it should when closed. Or maybe the odds were just running in your favor.

Given that I am highly skilled with hose clamps and that the odds seldom run in my favor, I just remove the heater hose as described to avoid the chance of a problem. The two minutes it adds to the job just isn't an issue with me. I am a recreational maintainer, anyway, so getting in a hurry just reduces my fun time.
 

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The problem occurs when air gets trapped in the head, behind the thermostat. A dry thermostat won't open as it should, and an overtemp condition results. If you are not having that problem, it could be that your thermostat is not sealing as it should when closed. Or maybe the odds were just running in your favor.

Given that I am highly skilled with hose clamps and that the odds seldom run in my favor, I just remove the heater hose as described to avoid the chance of a problem. The two minutes it adds to the job just isn't an issue with me. I am a recreational maintainer, anyway, so getting in a hurry just reduces my fun time.
most thermostats have a couple of 1/4 inch holes that bypasses the actual thermostat so that shouldn't be the cause..maybe I am just living right
 

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most thermostats have a couple of 1/4 inch holes that bypasses the actual thermostat so that shouldn't be the cause.
A vented thermostat will prevent the problem; that's why it's vented. For sure, there are plenty of thermostat models that are not vented and have the propensity to trap air behind them.

Please tell me where to find a 4.0L thermostat with two 1/4" vent holes. I would like to see it.
 

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A vented thermostat will prevent the problem; that's why it's vented. For sure, there are plenty of thermostat models that are not vented and have the propensity to trap air behind them.

Please tell me where to find a 4.0L thermostat with two 1/4" vent holes. I would like to see it.
I can't say that the ones for the 4.0 is vented but the majority if not all the thermostats that I have changed over the years in other vehicles were..I gather by your reply that none of the 4.0's are..correct ??
 

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I didn't have air lock when I did flush and fill last month but I know the heater hose trick already and didn't need it (this time)
 
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