Thermostat or water pump

[85Renegade]

Hello all,

I have done a fair bit of searching but finding no cj specific, definitive answer to my question. My 1985 CJ7 6cyl AMC 258 i6 / 4.2l is overheating. Here is the symptoms as I drive the jeep the needle keeps climbing, however the very very top of the radiator is super hot the top hose from the thermostat housing to the radiator is hot, the hose to the intake manifold is also super hot however the lower hose from the radiator is cold and so are the hoses going to the heater core.. is this a thermostat issue or a water pump failure?

Thanks in advance

 

[mtnwhlr]

It sounds like a stuck Thermostat.

 

[85Renegade]

That's what I'm hoping for what are the symptoms of a bad water pump?

 

[Torxhead]

When a water pump goes bad its usually a worn shaft bearing that causes an exterior leak. Your cooling system could be clogged also, requiring a cleanout.

 

[Posi]

You say the top hose is hot and the bottom hose is cold, sounds correct to me. The top hose being hot tells me the thermostat is open, it then travels through the radiator where it's cooled by the fins and exits the lower hose cooler then it went in the top, then enters the water pump.

You may have some blockage elsewhere (radiator/heater core/block etc), have you back flushed the system? You mentioned the needle raises but didn't mention to what temp?

 

[Sasquach]

It sounds like a stuck Thermostat.

^Sounds like a good place to start, well maybe not.
When I first got my 5 it ran hot but the radiator front was covered by an aftermarket air conditioning condensor, got rid of that and problem solved.

 

[85Renegade]

Sorry the needle goes all the way to max and steam exits out of the overflow tank.... It doesn't seem like water is flowing through the radiator the entire radiator is cold except for the very most top part of it... And the lower hose is unnaturally cold.. I'd say 55 degree like outside air temperature.

 

[Posi]

As mentioned you need to flush the system to find the restriction could be the radiator or elsewhere.

 

[85Renegade]

I'll look into it.... Does it also sound like a thermostat issue?

 

[IOPort51]

Air pocket, these things can be a major PITA to fill with coolant. get it hot with the cap off and be sure you get all the air out and it has circulation. sometimes you can pull the temp sending unit to burp it. ( do this cold).

 

[Posi]

If the top hose is hot the thermostat is open, if it's open the thermostat will not be the cause of an overheat issue.

First thing I would do is inspect the water pump for leaks especially under the pump where there is a weep hole. Then check the radiator for a restriction being the top is hot and bottom is abnormally cold. If you still haven't found the problem flush the system, you will need to remove the thermostat to do so. While you have the thermostat out check it's function by putting it in a pan of water, heat the water, the gate should open fully as the water heats. Make sure you back flush the heater core as well.

Edit: IOPort51's post raises a question, before it overheated did you recently add, emptied, or changed out the antifreeze?

 

[85Renegade]

I found some free time so I figured I would try to sort out my over heating issues... I picked up a thermostat, gasket, coolant and radiator cap from advanced, and had at it....

Here is where we will be working. The thermostat housing...





Removed the radiator cap to expose what was beneath...








Then started removing hoses...



I'd say I missed the bucket a bit...



Got out the hose and began flushing the radiator and the the engine...



Here is the color of the coolant.. Not horrible... Reminds me of ecoto cooler from hi-c



Housing off.... It's just a 1/2 inch nut and bolt...






Old thermostat...



Where the thermostat lives...



New thermostat and gasket..







Installed..



Now I've read alot about people having leaks etc etc using gasket maker... I'm a big supporter of torque specs and believe it's 90% of people's issues... To tight is not necessarily better... I bolted this down to 18ftlb as speced



All buttoned up...



Coolant I like to cut it myself I feel it comes out cheaper.... 50/50 with distilled water...

 

[85Renegade]

Toped off..



I drove the balls off the jeep let it idle then drove her again.. This is as high as she would get... I'd say problem solved...



A new cap for good measure....

 

[IOPort51]

 

[Posi]

For kicks, can you toss the old thermostat in a pan of water, turn up the heat, then video the gate action?

 

[85Renegade]

Let me see if I threw it out I typically don't throw anything out.... If I got it sure y not I always wanted to see it happen too

 

[IOPort51]

Of course if it works it means you did not have a bad thermostat.

 

[Posi]

That is why I asked the OP to test the thermostat in post 11 and 15 of this thread.

If we really want to help others we need to follow through and come to a conclusion. You can say "I'd say problem solved" but we won't know if it's the thermostat unless you test it. It could have been an air bubble, or a restriction, could be a thermostat not fully opening, or that you didn't have the proper amount of antifreeze (should cover the tubes) according to the order of your pics.

 

[mtnwhlr]

I will bet it was the Thermostat like I said at the beginning.

 

[Posi]

It very well could be, but lets test it to be sure. The pics tell us the thermostat when cold is closed, we also know the top hose is hot, which means the thermostat opens. If the thermostat is faulty chances are it's not opening fully which would cause a restriction.

however the very very top of the radiator is super hot the top hose from the thermostat housing to the radiator is hot,