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Any tips for changing the thermostat?

2K views 9 replies 7 participants last post by  RECox286 
#1 ·
Thanks for all the help so far with the emissions saga here. Seems the thermostat is probably stuck open, and since the engine is running too cool - like 150 - it is running rich, and that might be some of my high HC problem now. I realize I probably will need a new CAT as well at some point, but hoping to put that off until I can visit my grandpa and his shop up in Sacramento. :mrgreen:

I think I'm going to put a stock 195 thermostat in. Does anyone have any tips for me on the replacement procedure or things to look out for when I do this? Hoping to do it this afternoon after work. Also, the two parts stores close are O'Reilly's and Autozone. Not sure if there is a particular brand that is better, looks like they sell different brands.

Thanks guys, I REALLY appreciate all the help so far!
 
#2 ·
On my 89, the thermostat is kind of difficult to reach. There's a bunch of AC components blocking things. Yours is close in years. Might present similarly.

Drain some coolant from the radiator drain at the bottom. Consider draining it all and replacing. Disconnect the upper radiator hose from the radiator. That gives you a convenient "handle" to lift off the hot water neck. You may need to disconnect the same hose from the neck side as well if the hose clamp is in the way of the nuts. Hope you don't. That will be tight. Loosen and remove the two nuts that hold the filler neck to the engine. Try and get the nuts to come up, away from the engine as you remove the socket. Some people use grease or wax in the socket to capture the nut. Once the neck is removed, LOOK at the thermostat before removing and see which way it's pointed. Pull it off (may take a bit of force) and remove/scrape off the gasket.

Then do the reverse. Clean the gasket surface well. Consider replacing the upper (and lower) radiator hoses while you're there. And as long as you're there, check the ground bolt/stud/nut near there is tight. It's a ground wire/strap that connects the engine to ground. Just make sure it's tight.

When finished and buttoned up, fill with 50/50 coolant and water. Leave the radiator cap off, start and idle the engine. Once the thermostat opens (at 195) you'll see the coolant level drop in the radiator filler neck. Continue to add coolant and water there till it won't take any more. Replace radiator cap, fill overflow reservoir to appropriate level. For the first few hours/days, check the coolant level OFTEN. Air will burp itself out of the system and need to be replaced with fluid. Run your heater(s) to circulate the juice through everything.

Dispose of the coolant responsibly. Use green or yellow coolant (Ethylene glycol) not DexCool.

Lump
 
#6 ·
OK, I will definitely do that boiling water test! I agree, what a lot of work to do and then put a defective part back in!

@Lump - thanks for all the tips, they will come in handy. I like the idea of using the upper hose for a handle, that sounds like a good one! ;)
 
#7 ·
Alright! The project is complete. :cheers:
Wanted to give a big thank you to everyone for the help, and especially Lump for all the good tips and to Chevymaher for the good PMs. Thanks guys. Oh and go figure - someone had put a 160 degree thermostat in there! Man...I'll bet that was a big part of the problem, it even sounds different when you romp on it now. :mrgreen:
So now it will even idle at 200 - and stays there, even when I'm rodding on it going 80 on the freeway.

I'm going to take her in tomorrow and see if she passes now. Engine sure sounds good. Here's a list of everything that I've replaced so far:
EGR valve - California style
O2 sensor
Thermostat - back to stock 195
Bosch Platinum plugs
Cap and rotor- brass
Fuel filter
PCV valve
Air filter
Wires were already Bosch 7mm aftermarket - so I left them. Would like to upgrade to 8mm Accel wires, and coil, etc someday... Well, That's it I guess. Hopefully it passes good tomorrow!
 
#10 ·
Changing the Thermostat (short FSM version):

Removal:

Step 1...Remove the Thermostat

Installation:

Installation is the reverse of Removal

Uncle Bob

( Note: Try to remember how the T-stat sits in the cavity during Step 1.)
 
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