Write-Up: Thermostat Installation

I could see the metal-to-metal thermostat housing on the engine block developing a leak if a proper seal could not be created due to lack of a gasket. It's cheap and safe just to do both of them.

Images and additional comments (in blue) added by AA, 01/08/12

Tools Required:
10mm wrench or socket

Materials needed:
Thermostat (180* recommended) - Intense P/N TST-180 or other brand
Thermostat seal - Fel-Pro P/N 35666 or other brand
Thermostat Housing Gasket - Fel-Pro P/N 35595 or other brand

Difficulty:
*****

Instructions:

*first read albertj & BillBoost37's post below before proceeding*

(1) Locate Thermostat Housing AA: right side of engine, near intake/throttle body, connected to upper coolant hose.


AA: for less mess, place a drain pan under the area. A flex funnel can be used to direct spilled coolant into the pan. 3-4 shop towels placed around the housing area will catch the rest.


(2) Carefully unplug any vacuum lines obscuring your access to the 10mm bolts on the upper Thermostat housing
AA: you may not need to remove any lines. I was able to find access for a socket at both screws.


(3) Remove the Thermostat Housing Bolts and loosen the upper housing

(4) Move the Upper Thermostat Housing Body attached to the hose out of your way.


(5) Remove the old gasket and clean the ends of both the upper and lower Thermostat housing (Scraping maybe required to remove the old gasket from both the lower & upper Thermostat Housing.)
AA: if the old gasket remains intact on the upper housing, it is possible to reuse. Inspect the gasket and replace if it appears deteriorated, or has been leaking.

(6) Remove the old Thermostat


(7) Place the new Thermostat seal around the new Thermostat. (Look at your old Thermostat to correctly install the seal right end up) AA: note damage to seal in previous image.


(8) Install the new Thermostat with seal, spring side down


(9) Place the new Thermostat gasket on the lower housing AA: (if necessary)

(10) Replace the Upper Thermostat Housing Body and finger tighten both bolts


(11) Tighten both bolts on the housing equally using the 10mm wrench or socket, making sure the bolts are tightened evenly. AA: tighten screws to 20 ft-lb.

(12) Replug any vacuum lines you removed

(13) Start the engine and let the temperature on your gauge reach 180* plus. Check for leaks around the housing.

Nice job!

The wifes 99 Riv has a "bleeder" screw on the thermostat housing.

Bert:tavis:

mine does too.....what's that for? Releasing the pressure before you remove the upper housing? I guess if you needed to change the thermostat while the engine was still hot that would make sense....

Hi, Mark

The bleeder screw on the thermostat housing is for releasing air trapped in cooling system if and when it's the case that the radiator cap is not the high point when you open the cooling system and close it back up. It just let's you bleed off trapped air.

You definitely have to open the bleeder when you fill coolant after a compete drain and flush. And it is good practice to check it after replacing a cooling component.

Albertj

I would suggest adding removing 3/4 of a gallon of coolant and adding it back in to the procedures along with the burping process.

Looks great.

I ordered a 180deg. thermostat from ZZP. It came with rubber o-ring instead of a regular gasket.

Do I need to get a gasket or is this o-ring all I need to use?

Any issues I need to know about with this replacement?

There is both an O-Ring type seal (look closely at it. It wraps around the thermostat. There is a groove in the middle of the seal.) and a gasket.
You can pick up the gasket at the local auto parts store before you do the job. I always replace both, no sealant required. Other than that it is a straight forward thermostat R&R job.

Yes, get the regular flat gasket from local parts store, FOR SURE.

You might be able to reuse the gasket (flat paper) that's on the car. I have changed my T-stat about 6 times, but only used a new gasket once. I do not use silicone RTV to install, never had a leak yet.

was just wondering do i need new gasket and o-ring? and also do you need to drain the entire system, or just enough to get it out of the upper hose?

Yes, replace both the gasket and o-ring. No need to drain the whole system. Be sure you bleed all the air out when you refill, with the bleed screw on the t-stat housing.

bleed screw? sorry im not too familiar with this.

There is an air bleed screw built into the top of the thermostat housing. I'd assume your 97 has it also? When you're all put back together and filled with coolant, you run the engine til it's warm enough for the thermostat to open, then crack open the screwa bit to let trapped air escape. Air in the system is not good.

ok thx for the tip

I had a leak after replacing my T STAT and found out that you do not need the gasket if you use the O RING.
I removed my gasket and the leak stopped completely.

EASHER wrote:

I had a leak after replacing my T STAT and found out that you do not need the gasket if you use the O RING.
I removed my gasket and the leak stopped completely.

I didn't want to take chances. I used the gasket w/ some rtv and no leaks.
Next time I will use the gasket again.... Come to think of it, Ive never not used a gasket

The gasket and o-ring combo was not used in all the model years from the factory. It IS listed for the later models for sure. I replaced both last year when I did my 180. No sealing issues. You need to completely remove the old gasket, probably requiring that you scrape it all off, I had to do quite a bit of scraping. If you don't have clean mating surfaces, you won't have a good seal.

I did see a few years of SI 3800s that had both, and I've seen quite a few 3800 thermostats that had only an O-ring and never leaked. I prefer the O-ring, much easier to change and no gasket scraping needed. I would only use one or the other.

deekster_caddy wrote:

I did see a few years of SI 3800s that had both, and I've seen quite a few 3800 thermostats that had only an O-ring and never leaked. I prefer the O-ring, much easier to change and no gasket scraping needed. I would only use one or the other.

lol i have both....

so should i get both or just an o ring or just a gasket?

I have them both, always have. No silicone used ever.

ok, and do i need to drain the coolant or not? chicken's writeup has me worried

Just use some paper towels to soak up the spill. It's enough lost coolant that you'll want to replace it, but not enough that you can't drive before refilling. Shouldn't need to drain coolant for a T-stat install.

like how much coolant are we talking?