Right before the trip up to Michigan last July, I swapped out all my cooling hoses, thermostat and thermostat housing, swapped in a new 2 core radiator/shroud/fan clutch. Ever since then, I have had two annoying little drips, plus another strange phenomenon.
1.) Radiator drain cock always has a drip on it.
2.) Little leak on top of water pump after it cools down.
3.) This started the other day, but if I start it up and go straight out to the interstate before it fully warms up, it runs at 220 and will NOT drop unless I shut the engine off for 10 seconds (I throw it in neutral and coast). Upon restart, it has dropped to 195/200 and stays there. I thought this might just be the VDO gauge, but the speedo temp gauge and the scan tool confirm this phenomenon.
Finally got tired of smelling anti freeze when I walk around the front of the Jeep, so I worked on my Red Scrambler this morning and fixed all three issues.
Some new parts, only one of them is interesting, and it explains a problem I had when I reassembled this stuff before the Michigan trip.
The two new hose clamps fixed the little leak below the thermostat/above the water pump. When I pulled the two installed clamps off, the screws backed out of both clamps, so they were NOT maintaining torque. Pretty sure these two clamps came out the used/spares box. Simple fix.
I also removed the short bolt I had at the lower thermostat housing bolt hole and installed a stud, just to make reinstalling the thermostat housing easier. I should have done this BEFORE SandBlast, better late then never.
A new drain cock in the radiator fixed the annoying drip. The one I installed before SandBlast was one I pulled out a junk radiator. I assume it had some very slight damage at the sealing lip causing the little annoying drip. Easy fix, since I needed to drain the coolant to mess with the other parts.
The only "interesting" part:
A genuine Mopar replacement thermostat that comes with a little "air bleed hole/check valve thing". This style thermostat came with both my Mopar MPI kits and I never had a problem with them. Even when I pulled the 4.2 out of this Scrambler and swapped in the 4.0, I reused the original Mopar thermostat. Never had an issue until I swapped in a regular NAPA 195 degree thermostat.
NAPA on left, Mopar on right.
Now, back before SandBlast when I swapped in all of the new cooling hoses/parts, AND thermostat, I had a hell of a time bleeding air out of the cooling system. I never had so much drama. I burnt myself multiple times, wasted gallons of coolant, before it finally bled out. It took me like two hours to get all the air out!!.
On a 4.2, I will usually start up the engine with the upper heater hose loose, let it warm up some, gently pull the top of the hose barely off the heater core, let the air/some coolant out, slide it back on, done. A stock 4.2 has the two extra heater hoses plus the heated intake.
You would think a 4.0, or 4.2 with a 4.0 intake would be easier, less hoses and a not heated intake. Not for me, with the NAPA thermostat.
Now, is this miracle thermostat the reason for my phenomenon and major coolant air bleed issue? I no longer have the issue, and the coolant system bled itself out simply by letting the engine idle up to temp with the coolant cap off. No drama, done.
You could probably save yourself some money and drill a little 1/8" hole in the NAPA thermostat and get the same result. On a carbureted 4.2 I have always used regular thermostats and never had a problem. On a 4.0 or Mopar converted 4.2, I will use a "holy" thermostat. Lesson learned for me.
Miracle thermostat installed, the hole at the top/12 o'clock position, secured in place with a bit of aviation sealant to keep it from slipping out of position.
Verifying that the thermostat housing is "true/flat":
Used two bolts as alignment dowels to line up the gasket. After the gasket was stuck to the thermostat housing, I put a very thin coat of aviation sealant on the side of the gasket that goes against the head. Over kill maybe.
I added two flat washers on the bottom to get past the smooth non threaded shoulder of the stud.
All finished up. The 4.0 thermostat housing has a center stop on the large hose neck. I put a clamp above and below the center ridge. Overkill maybe, but I want to keep this damn thing from having that annoying cool down drip!!!
I drove the Scrambler around a bunch this afternoon. No more drips!!!
Should have painted that water pump when I swapped the engine in back in 2016!!!!
No leaks, and no more phantom "rise to 220 and stay there" issues. I plan on daily driving it this week, like I have been the last few weeks, so will be able to quickly tell if my fixes fixed it.
With the outside temp at around 50 today, 195 degree thermostat, it ran between 195-205, mainly between 200-205.
Hopefully that is it for cooling issues for awhile!!!
