Bad Thermostat led to compression test...

I'm slowly working my way through this Jeep I bought recently and replacing/repairing parts. I removed the thermostat, flushed the cooling system and then installed a new thermostat. Poured some gas into the tank (tank leaks), fired up the engine and monitored the temperature gage. The temperature gage headed for hot and when checking the thermostat housing realized that the thermo was not opening as the hose and housing were cool while the engine was hot. Ugh!!! now I have to replace a supposably good thermo. I'll test it on the stove first...

Anyway, since the engine was already hot, I decided to perform a compression test to check the engine condition. I did this with a bit of trepidation as I didn't know how well the PO had taken care of it. I was happy to measure

150-145-150-150-145-150 psi

Whew! At least that's one less thing I'll need to rebuild!

Then I went to look at the Master cylinder,(what a nasty place to put a it I'll upgrade it later), Anyway, it has a small plastic cap that you must twist of by hand and of course it doesn't.... I'll probably just buy a replacement Master cylinder and figure it out then.

Happy Jeeping!

 

Don, those master cylinder caps can be a bear. You want them tight to prevent contamination, but in my experience they don't need to be real tight, otherwise you get the condition you are in. The stock one on my Jeep had a metal cap with a nut made on the top, my replacement one had the plastic cap with a finger "ridge" I guess you call it. You might need to take some pliers to it. And be advised, those caps can easily crossthread when reinstalling, and the plastic cap threads aren't very forgiving of that, so take your time and be careful when reinstalling.

 

I actually like the plastic cap that came on my '66, and I swapped it into the '64's and sold the metal cap w/ nut made at the top. It was easier for me to service the MC. The metal nut cap requires a 1 1/8" socket, and wriggling room is limited. The plastic cap just needs 2 fingers or at worst, a pair of pliars to twist like Greg said.

 

I am running my plastic cap for just that reason, but have the metal cap and old MC in the "old parts box" (we all have one of those I bet). The metal cap on mine used a 3/4 or 7/8 wrench....

Here in the Marine Corps we have just had our old 5 ton 6x6's replaced with a 7 ton 6x6. The old M813's (stick shift 5 ton) had a hydraulic MC that operated an air brake system (hydraulic over air). The MC looked just like the single line MC on our old Jeeps. It used a metal cap with a large nut (1 1/8"?), we would use a BFcrescent wrench to get them off. They also had a metal vent line that screwed into a fitting on the cap that made it a pain to check the fluid. And of course, they were located beneath a small trap door on the floor inside the cab at the drivers feet! And we just phased those trucks out in 2002!

 

Hippo or Schardein: When did they change to the dual MC. My '68 has an ablong cap with a bolt in the center to hold it down.

 

Dual reservoir MC's came out in '67.

 

Greg,
Thanks for the info on the cap. I'll carefully apply pliers to it to see if that hopefully removes it. Then I'll continue on to the bleeding routine.
I picked up one of those hand vacuum pumps that bleeds the brakes without having to pump them. Hope that helps to simplify the process.

 

James, like Bob said, 1967. However mine has the single line. Everything points to mine being built late 66, then sold as a 67?? The front and rear diff carriers are date stamped Oct 66, the VIN date sheet I found on the net says my vin was biult Nov 66, but it is titled as a 67. Maybe mine was the last one built with single line MC?

I have one of those dual line MC with the single bolt in the center of the cover, NOS. Planning to some day convert using Herms conversion bracket.

 

Well if the system was completely empty, sometimes you will get that air pocket on the engine side of the thermostat. You look at your temp gauge and it's going to the moon in a hurry. Sometimes all you have to do is rev the engine a few times and that usually will work the air out of the system. That's why I like filling my cooling system with the thermostat out. I pour in coolant till I see it in the stat opening, then put the thermostat and housing on, then finih filling the system.

 

Don, I have the mityvac vacuum pump, among other things it bleeds brakes. I really like it, no bugging the wife to bleed the brakes. Also handy for checking vacuum advance and heater control diaphragms.

Ditto what John said on the air pockets. Seems like I have read/heard somewhere that a small 1/8 hole drilled in the thermostat can help alleviate that, and not really effect proper warmup and operation. Never tried it though.

I have seen bad thermos out of the box though. I usually buy the more exspensive ones at the FLAPS in the hope they are better. It's a good idea to check proper operation on the stove before install also. Of course its also a good idea to brush after every meal, refrain from tobacco and alcohol, always drive 5 mph below the speed limit, etc etc

 

That'll get you shot out here. It's 15 over the limit R) R) R)

 

only 15....here you'll barely hold the right lane @ that speed. 20-35 over is more like it.