Thermostat?

I have to replace the t-stat. Just wondering if it matters what orientation it goes into the housing. It has no holes as far as I can see... Its made by stant.

Also, do i just install the t-stat into the block, put the gasket over it, then the housing, and tighten?

Is it the stand thermostat (super stat) with the "v" notches?

When I used one of those I put one of the V notches at 12 O'Clock.

But yes, thermostat, gasket, then housing. Apply a light coating of RTV to the gasket if you want to.

drill a small hole in the housing to burp air from the system, 1/16 is about right, 1/8 is way to big. put the hole at 12 o'clock

Ive put it all back together already without a hole. How do i burp it? Also it feels like there is no coolant flowing in the large hose that comes from near the top of the rad to the tstat housing

So I am assuming i have to pressurize the system. My overflow is full, and i think the rad is full. Do i just run the truck with the rad cap off? Sorry noob here.

Jayposer2000 said:

Ive put it all back together already without a hole. How do i burp it? Also it feels like there is no coolant flowing in the large hose that comes from near the top of the rad to the tstat housing

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Next time your really going to want to have that hole in the thermostat.

Now that its all back together do this: (If you have a RENIX Jeep 87-90)

Wait till the engine is cool....

1.) Jack up the rear as high as you can and let it rest on jack stands.
2.) Slowly Remove the coolant temperature sending unit (its located at the back of the cylinder head almost directly below the MAP sensor) until you start to get coolant leaking from where the sending unit screws into. While doing this keep an eye on the coolant bottle. If it starts to get low, make sure you fill it up. DO NOT let it drop below the little chair in there, or else you will end up having to do this again in a few days.
3.) Once coolant starts to leak from this screw hole, tighten the sending unit back up, and replace everything else you may have removed. Lower the rear end and your done.
4.) I havent dont this, but it may be a good idea to do these steps again in about a week.


If you have a 91+ Jeep just make sure you have a good radiator cap. Its an open system so its self burping..
Hope that helps.

hijack in progress.

didnt want to start a new thread for this question.

when my rad overheated the other day, 1997 4L, the overflow bottle never got a drop. so this self burping found in the 91 and newer years doesn't seem to be working.
Would that be from a bad rad cap?
Or perhaps the hose from the rad to the overflow maybe plugged from some crap after the hose blew.

I am not sure if I have a hole in my t-stat, since I'll be replacing the head gasket anyway, is drilling the hole worth it?

As Muad'Dib says, all you need for an open system in 91+ XJs is a patient refill of coolant, a good 16# radiator cap, good hose from the radiator fill tube to the overflow bottle (someone recently asked if this hose was even necessary), and an overflow bottle about half full of coolant. I fill my bottle somewhat above the "full" mark and watch it after the first two or three heat/cool cycles. If everything is working properly, the level of coolant in the bottle will drop down to about the normal level.

I don't know if it actually necessary but I also check the coolant level at the radiator fill tube for the first couple of cycles and top it off as necessary.

Once again, just to be specific, you do not need a hole in the thermostat.

I guess a lot of this confusion about holes in the thermostat and complex burping derives from mixing questions and answers for the open and closed systems. It helps to include your Jeep year and motor in your post. We might guess that Jayposer2000 has a 2000 XJ 4.0 L but it sure will cut out a lot of extraneous and confusing info if that is stated explicitly.

You should at leave have one hole in the thermostat at ther 12:00 position.

These threads go on forever about holes in the thermostat. I can only speak anecdotally in saying that the thermostat in my '93 I just replaced didn't have a hole and my new one doesn't have a hole and I have had no problems burping or otherwise. Perhaps I've just been lucky.

In any event what would help me in understanding this to know exactly what having a hole will do for me with my post '90 XJ . I'm surely no expert and I am not being facetious in asking this question.

In the meantime, I am not on a crusade to save the XJ Nation from 'stat holes -- only from endless posts about same. For anyone who is uncomfortable without a hole in his or her thermostat, I agree that they should buy a unit with one or drill one.

Blaine B. said:

You should at leave have one hole in the thermostat at ther 12:00 position.

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EXPLAIN!!:dunno:

Pelican said:

In any event what would help me in understanding this to know exactly what having a hole will do for me with my post '90 XJ . I'm surely no expert and I am not being facetious in asking this question.

Click to expand...

5-90 is a good source for these types of answers:

5-90 from another thread said:

It makes the system self-purging of air, even if it should accumulate later due to, say, a compression leak. The upper hole passes air out of the engine, and the lower hole passes water into the engine, to displace the air.

Click to expand...

The holes should be drilled with a 1/16th drill bit. When installed one will be at 12 o'clock and the other at 6.

ColoradoRaptor said:

EXPLAIN!!:dunno:

Click to expand...

You should have at least one hold in the 12:00 position.

Like the OEM thermostats. Except they have the check ball.