4.0 Cooling system question

Van-go

Van-go

Not an old man
Joined
Dec 11, 2014
Location
Greensboro
I drove the YJ to Greensboro and back on Friday (45 min each way)
I noticed while going through a drive through on the way back that it was getting really hot.
Once I got back on the road it cooled down, but when I got home, the radiator was spewing coolant out of the bottom.

I had just replaced the radiator, cap, water pump, thermostat, and both temp sensors.
I am running an electric fan that runs all the time. (not sure of model but it keeps it cool enough on the trails)

The radiator is under warranty, so I pulled that to exchange it already...

Question:
What would cause this to happen? Do you think it is just a faulty radiator, or?
I want to avoid having this happen again if at all possible.

(I doubt they will give me another radiator if the same thing happens again.)
 
Could be a faulty radiator cap, or the cap doesn't fit properly on the new radiator, so not building cooling system pressure. Or, faulty radiator that is leaking and not building cooling system pressure. Actually, where is the radiator leaking from, and do you support it split from overpressure?

Or, faulty thermostat, maybe only partially opening. A surprising amount are bad out of the box. Easy to diagnose on the stove with a pot of water.

So you did the entire trip and didn't overheat continually, and still had enough coolant left to get home..?
 
Get the radiator pressure tester kit from Advance Auto, its free to borrow (actually a hefty deposit). The kit has sixty gazzilion fittings and adapters, one should fit your YJ. See if the system holds pressure overnight. If not, you might get luck and see or hear where its pushing coolant out, possibly even right when you start pressurizing it.

Now about that radiator, its been my experience that the type with plastic tanks crimped to an aluminum center section will fail at some point, and can be really tricky to ever find an exact leak point. They just leak all the way around after a while. That may not be the case with yours being under warranty still, just throwing that out there.

Another thing could be the lack of a fan shroud. My CJ would run real hot on the highway at high RPMS, backing down 200RPMs or so I could see the temp gauge drop dramatically. Added a fan shroud and it was all good.
 
Fabrik8 said:
Actually, where is the radiator leaking from, and do you support it split from overpressure?

Or, faulty thermostat, maybe only partially opening. A surprising amount are bad out of the box. Easy to diagnose on the stove with a pot of water.

So you did the entire trip and didn't overheat continually, and still had enough coolant left to get home..?
Click to expand...
It leaked from the bottom where the aluminum crimps to the plastic.
I know the t-stat worked when I installed it. Did the stove test. But it could have gone bad I guess.

It didn't heat up until I was in the cookout drive through back in Burlington. A couple miles from home.

When I got home the temp gauge was normal but the radiator began spewing.


6bc972f6264cd9f3f948305d39c3e361.jpg



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RenegadeT said:
Get the radiator pressure tester kit from Advance Auto, its free to borrow (actually a hefty deposit). The kit has sixty gazzilion fittings and adapters, one should fit your YJ. See if the system holds pressure overnight. If not, you might get luck and see or hear where its pushing coolant out, possibly even right when you start pressurizing it.

Now about that radiator, its been my experience that the type with plastic tanks crimped to an aluminum center section will fail at some point, and can be really tricky to ever find an exact leak point. They just leak all the way around after a while. That may not be the case with yours being under warranty still, just throwing that out there.

Another thing could be the lack of a fan shroud. My CJ would run real hot... Added a fan shroud and it was all good.
Click to expand...

Autozone radiators are the crappy style, but with a lifetime warranty, it's hard to beat.
They told me they would pay for new coolant too... We'll see.

I like the pressure test. I'll put it all together and see.

I don't have a fan shroud, but it's never been an issue before. (Had it a year or so)



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Did you bleed the cooling system after replacing the aforementioned parts? Air trapped around the impellor will cause an overheating condition.
Since it just happened after your repairs, I'd have to start there.
 
Jody Treadway said:
Did you bleed the cooling system after replacing the aforementioned parts? Air trapped around the impellor will cause an overheating condition.
Since it just happened after your repairs, I'd have to start there.
Click to expand...

Yep, and I looked it up and I did all the work at the end of July actually.

I was thinking and I did overheat it one other time on Daniel this December when the fuse blew for my electric fan...
I added fluid and have been on a couple trips since then with no issues.
 
Just went to Auto Zone and they gave me a new radiator, cap, and coolant for free. I'm gonna replace it all, check the T-stat again and put it all back together I guess...
 
I was checking a 4.0 for overheating . It had been diagnosed as a leaking head gasket. Owner bought a used motor for me to replace and was checking everything else before switching engines. It was low on coolant and I noticed a small vent in a thermostat from another motor. I tried that thermostat , filled with coolant and the original is running great
 
Van-go said:
Just went to Auto Zone and they gave me a new radiator, cap, and coolant for free. I'm gonna replace it all, check the T-stat again and put it all back together I guess...
Click to expand...

Did the thermostat you replaced or put in have a little weep hole at the top? The difference between a parts store thermostat and a dealer part is that tiny hole at the top. That small weep/breather hole stopped an overheating condition I had in a 99 xj.

It was interesting my current WJ 4.0 which I bought off of a friend had a small hole drilled into the thermostat when I replaced it the other week. I could tell it was not a factory thermostat too. From now on I always remember that if that small hole isn't there that I carefully drill one and sand down anything sharp leftover.

You can see the small weep/breather hole on this dealer t-stat. Most parts stores t-stats don't have that. (sorry the pic is huge)
Chrysler195thermostat_2.jpg
 
NickMaul said:
Did the thermostat you replaced or put in have a little weep hole at the top? The difference between a parts store thermostat and a dealer part is that tiny hole at the top. That small weep/breather hole stopped an overheating condition I had in a 99 xj.

It was interesting my current WJ 4.0 which I bought off of a friend had a small hole drilled into the thermostat when I replaced it the other week. I could tell it was not a factory thermostat too. From now on I always remember that if that small hole isn't there that I carefully drill one and sand down anything sharp leftover.

You can see the small weep/breather hole on this dealer t-stat. Most parts stores t-stats don't have that. (sorry the pic is huge)
Chrysler195thermostat_2.jpg
Click to expand...

I drilled it before I installed it. I just want to sure I didn't do something wrong before I have to warranty another radiator. Thanks for all the help guys.

Looks like only thing left to do is pressure test it...


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