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Discussion Starter #1 (Edited)
I know this may be somewhat an easy job for some people, but I have never changed a thermostat before. I am some what of a beginner in automotive stuff. I have a 1970 Mustang with a 302 V8. It also has a compresssor for air conditioning. When I took my Mustang out for a drive 2 weeks ago, the temperature gauge was a bit higher than usual. I see no real signs of overheating, but I have come to believe that the relief valve on the thermostat has been activated. I am going to try to change out my thermostat, but don't know what to expect when doing so. I have the tools to do it, but just don't know how to approach it. In addition, I don't know how to properly drain the radiator without making a mess. How should I approach this and what steps should I take?
 

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believe that the relief valve on the thermostat has been activated
I am not aware of any relief valve on a thermostat.
To change the t-stat you first need to drain the coolant from the radiator so that you don't dump coolant on the engine when you remove the radiator hose and thermostat housing. Then remove the upper radiator hose and the short 90* bend t-stat bypass hose. Now you can remove the 2 bolts that hold the t-stat housing to the intake manifold. The lower bolt is somewhat hidden behind the water pump and a socket and extension are needed to reach it. Once you have those 2 bolts removed the t-stat housing will come off although it may be stuck to the manifold with the gasket.
Get a new, name brand 195* t-stat. Do not believe those old wive's tales about using a 160* or 180* t-stat to keep the engine cool. They are lies. If the new t-stat does not have a small hole with a "wiggler" in it then drill a 1/8" hole through the flange and install it with the hole at the 12:00 o'clock position. This allows air to escape from behind the t-stat.
Be sure and note which way the t-stat faces. There is an "engine" side and a "hose" side and if you install it backwards it won't work. When you install it use a dab of RTV to hold the t'stat in position in the housing. If you don't stick it to the housing it can drop down out of place when you put the housing up to the manifold.
 

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Great beginner project,....not really too much more involved than changing the air filter!

You can do this!

I’ll even let you post this as a Build Thread. I’d like to follow, seriously.
 

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T-stat was the first project I ever did. I think I was 16. The new T-stat was bad. I overheated and ended up requiring a full valve job. I recommend that you test the new T-stat before you install it. You can do this by suspending it in pot of water on the stove. Use a candy thermometer to monitor the temperature of the water and ensure it opens when it should.
 

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I would advise you to do a flush to your coolant system first. Then go ahead and change the thermostat and distilled water and fresh antifreeze. You should probably get a new bypass hose and some hose clamps, Gently use pliers to wiggle the hoses once you loosen up the clamps. Oh, when you tighten the thermostat housing down try not to overtighten it until it makes that sickening crack sound...you'll know it when you hear it as an ''oh sh_t" moment. At least thats how I remember my first thermostat job...If all that doesn't get the temp back down, maybe its time for a new waterpump...your wrenching now for sure!!! Plus watch some youtube videos....
 

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You probably should know that though installing a fresh thermostat isn't a bad idea, it is extremely unlikely the new one will have any affect on the problem you believe you observed. If you use a less than good quality thermostat you may even introduce a problem. Just saying. Odds are you won't cause any harm though and changing a thermostat isn't a bad way to hone some mechanical skills.
 
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I didn't read through all of the previous comments, but, will add my recent experience doing just what you are seeking to learn. First, doing this in my garage, I wanted the least amount of coolant to flood my floor. Therefore, I placed a large shallow plastic tub that was wide enough to encompass the radiator and a portion extending to the oil pan, this I was hoping would, pretty much, assure any coolant will be contained. Now, I planned on replace the coolant, so, I released the bottom RAD hose first and dumped the coolant.

However, if you are replacing the T/S only.......
1. Do not remove the Rad cap. (leaving the cap in place captures the vacuum that is present. Be aware the T/S is lower than the top Rad hose, and to a certain extent, several inches below the top of the RAD. You will have less of a flood with the cap on as opposed to removing the RAD cap.
2. Anyway, release the top RAD hose to the T/S housing. You will lose coolant.
3. Next, disconnect the by-pass hose . It is a bit of a chore, due to its short radius, but, is manageable.
3. Remove the two T/S Bolts, and pull the housing free.
4. Recommendation, do drill an 1/8" hole in the rim of the new T/S. This will later aid in "burping" the block of air during the refill and engine warming process, Orient this hole at the top, when replacing.
5. The re-install is just best practices for applying a gasket material, a smear of gasket sealant etc. Torquing the bolts and re-installing the hoses.
I found on the start up, to have a screw driver, or whatever tool handy, depending on your clamp type, to tighten clamps, if needed, as the pressure rises.

BTW, having the "tub" in place, I had minimal coolant on a cardboard underlayment. Good Luck.
 

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I'll add my $0.02 worth....

a) You don't need to drill any holes in the thermostat. There is enough turbulence in the water flow to eventually force any air through, especially with the bypass hose present right next to the thermostat. Just try and orient the car so the nose is facing up hill (or the front tires on ramps) when filling and cycling the radiator through a heat cycle.

b) When you install the new thermostat, make sure you have the "bulb" portion (where it senses the heat of the coolant) facing IN toward the engine and not toward the hose. To make it easier to install, grab some dental floss, loop it through the "cage" portion of the thermostat that supports the "stem"... the part that IS facing toward the hose... run it out the thermostat housing and loop around the radiator hose nipple. That will hold the thermostat in place. When you have the housing snug on the intake manifold grab one side, snip the other and pull it out and throw away. Why dental floss? It's really thin but relatively strong. It's waxy-slippery. If you break it and can't get it out then just leave it... it won't hurt anything and over time will disintegrate.

c) FWIW, the purpose of the thermostat is to regulate MINIMUM engine temperature only. Replacing it, unless it is failing to open, will not affect the operating temperature of the engine, if it's getting warmer than normal. That's a sign of another issue. Since it's not a bad idea to change it anyway, you can remove it and reinstall the thermostat housing without a thermostat in it, do a "coolant system flush", then when everything is clean, install your new thermostat and coolant. I recommend Mercedes-Benz branded Citric Acid-based radiator flush. You can Google/Search for "Mercedes Douche".
 

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A typical coolant flush is a great way to remove all the old coolant to get ready to put in new coolant. Otherwise, it doesn't accomplish much.

Dollars to doughnuts, your radiator is clogged and should be serviced by a good, local shop. They can boil it out or do a "Rod Out" if necessary.

Now, the problem is your engine likely has a lot of gunk in the cooling system and that's what's clogging the radiator. So, if you put a clean radiator back into the cooling system, it will again clog. Therefore, I would suggest flushing your cooling system with ascorbic acid. You can buy it online. Do a search here for what some call a "Mercedes Douche". That will remove all the gunk from your engine block.

It's possible the ascorbic acid flush will also clean out your radiator, but don't count on it. I suppose you could run straight water for a good, long test drive to see if the overheating issue is gone. If it is, cool (literally). Refill with 50/50 and you're good. If it still runs hot, remove the radiator and have it serviced. When you reinstall it, it won't immediately clog again.
 
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