My 1995 Wrangler is consistently running hot (about 225 degrees, just short of red). It seems like I need to replace my thermostat (it's been at least 5 years since this has been done) and this time I'm going to try to do it myself.

I've read/heard that some or all of the coolant should be drained from the radiator in order to do this. Is this really necessary? If the engine is completely cooled can I just replace the thermostat and gasket? Is there anything else I need to know/worry about?

1/24/2009 1:04:32 PM

drain/flush of the coolant would be appropriate at this time, and probably make it a little easier to do it

1/24/2009 1:07:49 PM

5 minute job if its the 4.0l, dont know about the 2.5

1/24/2009 8:40:27 PM

^same thing. the motor just has 2 less pistons.

1/24/2009 8:57:59 PM

1/25/2009 9:41:27 AM

Did one on a 5.2 last night, as always the "hard" part is refilling the system.

1/25/2009 10:10:46 AM

not if you drill a small hole in the t-stat and fill it slow

1/25/2009 12:27:32 PM

Well, I just finished replacing the thermostat. I didn't drain and flush the coolant - I didn't loose any when I removed the housing and thermostat so I just topped off the reservoir when I was done.

Unfortunately when I was done I turned the engine on and let it run for about 5 min and it was already running up at around 220 degrees. The radiator itself seems to have plenty of coolant in it and it doesn't seem like I'm loosing any fluid. I guess the problem could be a bad water pump. Any thoughts?

1/25/2009 4:29:51 PM

system is airlocked, run it with the radiotor cap off, it will eventually blow out a shitload of steam/water, let it cool, refill, wash/rinse/repeat until all the air pockets are gone

just dont let it get too hot

1/25/2009 4:48:26 PM

was it overheating while driving down the road or just in stop and go traffic?

could be your fan clutch

1/25/2009 5:54:54 PM

It hasn't gotten into the red. It will run just short of red regardless of driving conditions - the same if it's resting at idle or going down the highway.

1/25/2009 6:24:28 PM

the reason for that being is that you have a steam pocket behind the thermostat and temp sensor, it will not read any higher until all the coolant flashes to steam and has blown out of the system

thermostats don't work well in air, which is why it isnt opening, if you have to, take it out and drill a small hole in the flange on it

1/25/2009 6:32:43 PM

Actually the old one did have a small hole/valve in it. The one I replaced it with does not.

Do I need to be adding coolant anywhere other than in the reservoir? There's coolant in the radiator to about 1.5" to 2" below where the cap screws on.

[Edited on January 25, 2009 at 6:45 PM. Reason : ]

1/25/2009 6:36:50 PM

when you took the top hose/t-stat housing off, did any coolant pour out? or was there an airspace in the head?


if it was, that was your problem

1/25/2009 6:42:14 PM

There was virtually no coolant that spilled out.

1/25/2009 6:46:25 PM

run it with the radiator cap off and keep filling it as it lowers

1/25/2009 6:53:12 PM

^ will not work

you really have two options, either take off a heater hose and try to bleed it, or drill a hole in the t-stat and very slowly fill it with the front parked uphill

[Edited on January 25, 2009 at 6:56 PM. Reason : make sure the hole is at the top]

1/25/2009 6:55:27 PM

Should I just put the old one back in? It's seeming like it may not have been the problem.

1/25/2009 6:57:45 PM

it's not that difficult on this engine,

you need the correct thermostat, with an air bleed hole,

make sure the flattest side faces the radiator, hole straight up,

then SLOWLY fill the system, do not let the top tank of the radiator fill up, if you do, it will fill the top hose and air lock it

once it stops gurgling, and you can still see a little coolant over the tubes in the radiator, start the engine and let it warm up, topping it off slowly as it goes down,

when it's warm you should see the coolant flowing, if not, let it cool off and try it again,

i usually dump in the antifreeze first, then top off with clear water, when you see bright green flowing into the top, you know it's circulating

you will still need to check and top off the reservoir every once in a while for a few days afterward

ok, try this first before you tear it back down:

take off the small heater hose that connects to the thermostat housing, and see if coolant pours out with the radiator cap off, if not then add coolant to the radiator until it pours out then stick the hose back on and try to warm it up










[Edited on January 25, 2009 at 7:20 PM. Reason : report back with results]

1/25/2009 7:04:20 PM

I had a wrangler 2.5 that use to over heat. Checked everything from t-stat to fan clutch. Finally tried running without a t-stat even installed and it still overheated. Ended up being a stopped up rad. 200 bucks and a single row alum. rad installed and it stayed cool. It's not worth trying to boil (clean) to original rad.

1/25/2009 7:23:04 PM

^^The heater hose is the smaller of the two hoses that connects to the housing, right (the one that tracks back towards the dash)? It's stuck on there pretty good. Any tricks to ease it off, I don't want to mess up the hose and have something else to fix.

^I just had the radiator replaced in the last year do it shouldn't be the problem.

1/25/2009 7:33:11 PM

if there is a long enough straight section past the nipple, cut it off flush with the nipple, then slit the remainder along the length and peel it off, and clean up the nipple with some sandpaper, then just push the hose back on with a new clamp when you're done

if not, work around it with a flat screwdriver and pry it off from the bottom, pulling will get you nowhere, but seriously, heater hose is cheap, if in doubt hack it off and replace it

fyi, never reuse the stock spring clamps, they really are a one time use deal and lose their tension, always replace them with worm drive clamps when you have to take them off

1/25/2009 7:54:21 PM

I'll get into this another day and let you know how it goes. Thanks for the help so far!

1/25/2009 8:11:30 PM

update?

1/30/2009 10:49:47 PM

My bad. I was able to cycle through the engine blowing off steam which did help bring the temp down. It was still heating strangely so I broke down and took it to a garage. Turns our my water pump and a lower hose were both leaking a little so I had them replace them. I was afraid if I tinkered with it any more I'd just mess something up.

Thanks for the help everyone.

1/31/2009 3:34:49 PM