Im lost...need suggestions

[jmeti000]

My 87' 4.0 manual tranny started running hot...at least for it. Last year I swapped over to the open cooling system, heavy duty zj fan clutch, and put in a new water pump, t-stat and sensor. After all that, my temp dropped about 40 degrees...and yes im being serious. It would run around 170-180 without fail. I started thinkin maybe the t-stat was stuck open, and ended up going through about 3 of them before I finally gave up. So here we are, and as of two days ago it ran just as described above. I havent been driving it as much lately, and after sitting for two days I took it out and all of the sudden it gets to about 220-30 while driving on the highway. It tends to inch up the most when pulling hills, and drops a bit on desceleration (sometimes it will linger around 210, but normally a bit higher).

I Brought it home, checked for leaks, cracks, water in the oil, all the normal stuff you would check for, flushed it out and put new fluid in and took it for a spin. It started to climb pretty quick, but when it hit 210 for the first time I could tell my t-stat opened up and sucked water out of the bottle....so I pulled over and filled it up again....and again. No change in temps, still runs hot. The system seems to be holding pressure well, cuz everytime I pull the little lever it spews into the overflow bottle like it should, and Im not loosing coolant anywhere.

I thought perhaps the tranny was gettin to hot, but its a manual and shouldnt really affect the cooling system...right? It got to dark to check that tonight, but its on the menu for tomorrow.

Im really thrown for a loop on this...any ideas?

 

[joe_peters]

Ok. no disrespect but I don't think you have a grasp on the open cooling system operation.

First, there should be no air in the cooling system. None. When the coolant in the cooling system heats up it expands. The expanded coolant must exit the system--Pascal's Law, fluids aren't compressable--therefore the two-way radiator cap, over flow hose, and coolant recovery bottle. As the coolant cools down, a vacuum is created in the cooling system and coolant is sucked back from the recovery bottle, through the overflow hose, and into the cooling system.

Now, for the system to function correctly there must be certain conditions present. First, the cooling system must be air tight--no leaks. One of the first things to do is trash the lever cap and get a good cap preferably with a 16 psi rating--the counter monkey will insist you have to have a 13 psi cap, but don't accept that. Next, all of air must be out of the cooling system, and the recovery bottle must be filled to the COLD line with coolant. Now, the overflow hose must either be attached to a nipple on the overflow bottles lower area, or, if it is the hose down through the top of the bottle type the end of the overflow hose must be resting at the very bottom of the recovery bottle. In other words, with coolant always to the COLD level when cool, when the coolant expands there is room in the recovery bottle to receive the expanded coolant, and the nipple/end of the overflow hose will ALWAYS remain covered with coolant so no air can be sucked back into the cooling system.

Ok, on we go. What temperature thermostat did you put in? You can't run colder than the thermostat's rating, if it functions correctly, because the thermostat will close, cutting off almost all of the coolant flow except for what the bypass allows and the engine will heat up, the thermostat will open, the engine should continue to heat up to "normal" operating temperature--higher than the thermostat's rating.

Ok, as to the super cool running. Gauge sending units go bad, they get scale developed on the part extending into the water jacket, or too much non-conductive thread sealer is applied at installation. It is NPT threaded and brass so it should seal without a thread sealant. It is a single-wire sensor, so it MUST ground through the sensor body, non-conductive thread sealer will screw with the resistance and the gauge's reading will be inaccurate.

So, I hope some of this will help you work towards a solution.

Good luck.

 

[jmeti000]

thanks joe...you hit the nail on the head with the temp thing and the cap. I did have some thread sealer on the temp sensor from when I moved it to the T-stat housing.

As for the cap...its the non-vented version lol. Didnt even think about it when I had an issue while moving cross country few months ago and the only place open was wal-mart...just walked in and grabbed the first cap listed for the jeep not even thinkin :doh:. Anyways, thanks again for all your help.

 

[jmeti000]

ok, no dice...changed the cap and the sensor out, and still get the same running temps. Its only when its at higher rpm's...mainly freeway driving. If its just going through town or idling the temp will drop, but the minute I get going freeway speeds again, it jumps back up.

 

[joe_peters]

Ok.

Check out this FAQ page on flowkooler.com, scroll down a bit to the overheating section:

http://flowkooler.com/cooling_faq/

 

[jmeti000]

Im pretty sure I found the culprit. I decided while I had everything apart I might as well boil the thermostat...It didnt start to open till about 220...and thats just BARELY opening up. Sseems a little high for a 195. Anyways, went and bought a new one, came home and tested it to be sure...wouldnt you know, opened up at 195. Thanks for your help joe. Much appreciated

 

[joe_peters]

Glad you got it sorted out.

Little late, but I only install Stant SuperStat Premium thermostats.