Replace thermostat without draining fluid?

[Turbo4whl]

So I just finished my coolant flush and silly old me forgot to put the thermostat back in before filling it to the to with new coolant. Can I put a glove around the upper radiator hose to plug the fluid so I can replace the t-stat without draining the fluid below the housing? Thanks.


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There is a way to keep the coolant in the engine, but not very convent without all the items. Years ago our shop repaired radiators and to test them rubber expansion plugs would be installed. One plug would have a small hose barb. Then dunked into the tank and add a few pounds of air pressure to check for leaks.

A fellow mechanic had leaking freeze plug on a medium duty truck. He took one of the expansion plugs with the hose port and installed it in the radiator fill. Using a vacuum pump, he pulled a vacuum on the full coolant system. When he tapped out the freeze plug,(about the size of a half dollar coin) there to my surprise is the coolant in the block, not a drop of it flowing out the open freeze plug hole.

 

[thecantaloupeman]

The gasket doesn't matter which side is up because it's a basic shape, it's the same either way.

The important part is making sure the bolts are tight enough (but not too tight where you blow the gasket out), and you also want to make sure the surface where the gasket seals is clean before you put the new gasket on. If there's remnants of the old gasket left behind or just crusty crud that gets on/under the gasket it will not seal well. A gasket needs to be evenly pressed between two flat metal surfaces. If you have to go in there with a razor blade or paint scraper to get the old gasket off, that's what you gotta do (especially if the guy before you put silicone or something on there). You need to completely remove the old gasket.

Yeah I did a pretty good job of cleaning it with a razor blade. I think the gasket just shifted slightly to one side when I put it on because it only leaks a bit from the one side that is slightly shifted. I don’t wanna drain it again so I’m just gonna loosen the bolts, hold the housing down and then quickly readjust the gasket.


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[80BrownK10]

Yeah I did a pretty good job of cleaning it with a razor blade. I think the gasket just shifted slightly to one side when I put it on because it only leaks a bit from the one side that is slightly shifted. I don’t wanna drain it again so I’m just gonna loosen the bolts, hold the housing down and then quickly readjust the gasket.


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I bet it still leaks. The gasket had holes for the bolts right? I don't see how it could possibly shift enough to get out from between the block and the housing?

Buy a new housing and be done with it, if you ha e been chasing this rabbit a few times already.

 

[thecantaloupeman]

I bet it still leaks. The gasket had holes for the bolts right? I don't see how it could possibly shift enough to get out from between the block and the housing?

Buy a new housing and be done with it, if you ha e been chasing this rabbit a few times already.

The bolt holes didn’t line up perfectly either. They were not the shape of the bolt. They are longer for some reason.


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[SquareRoot]

Drain the coolant, remove the upper hose, thermostat housing and thermostat. Clean the mating surface and the manifold mating surface with a gasket scraper or razorblade. Wipe the surface clean with acetone or alcohol. Put a light coat of rtv on both sides of the gasket. Don't make a bead, spread it paper thin with your finger. Position the gasket on the manifold. The rtv will hold it in place. Install thermostat making sure it's centered in the opening. There is usually a small recess that it sits in. If it's not centered it will leak like you described. Install bolts making sure they not bottoming out before the gasket is clamped tight. Usually, one of the holes is blind and the other goes into the water jacket. Confirm this and use thread sealer on the bolt threads. Wait an hour to be safe and refill the coolant.
This is as step by step as you can get. Do it once and be done with it. Done this a million times myself, never an issue... except, with the POS o-ring housings that I refuse to use anymore for the exact reason. They rarely seal properly. Go get em tiger.

 

[Rusty Nail]

There is a way to keep the coolant in the engine, but not very convent without all the items. Years ago our shop repaired radiators and to test them rubber expansion plugs would be installed. One plug would have a small hose barb. Then dunked into the tank and add a few pounds of air pressure to check for leaks.

A fellow mechanic had leaking freeze plug on a medium duty truck. He took one of the expansion plugs with the hose port and installed it in the radiator fill. Using a vacuum pump, he pulled a vacuum on the full coolant system. When he tapped out the freeze plug,(about the size of a half dollar coin) there to my surprise is the coolant in the block, not a drop of it flowing out the open freeze plug hole.

This one time, at band camp ,

Nah for real - a long time ago in the Jiffy Lube I worked at in high school, I had a leaking drain plug / post oil change .

To my amazement, manager dude held a vacuum cleaner over the oil fill in the freaking valve cover ! and I was able to change that gasket, with the crankcase full of oil and not leak a drop.

Sure I like to think that I was much more impressionable then but damnit man, that was NEAT!

Thought I'd share.
Keep the change!

Mmmmm.....Alison Hannigan...

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[Goldie Driver]

One time, and band camp ,

Nah for real - a long time ago in the Jiffy Lube I worked at in high school, I had a leaking drain plug / post oil change .

To my amazement, manager dude held a vacuum cleaner over the oil fill in the freaking valve cover ! and I was able to change that gasket, with the crankcase full of oil and not leak a drop.

Sure I like to think that I was much more impressionable then but damnit man, the was NEAT!

Thought I'd share.
Keep the change!

Mmmmm.....Alison Hannigan...

xc_hide_links_from_guests_guests_error_hide_media

I am assuming shop vac, but still.

Jiffy Lube with bulk oil in the back dispensed by guns on reels in the front - surprised they did not let it drain .

Cool trick!

 

[Matt69olds]

Referring to gaskets with less than perfect fit, as a Oldsmobile enthusiast unless I specifically ask for a Fel-Pro, some manufacturers will sell a gasket that also fits AMC 258 inline six. The gasket has the bolt holes elongated, I’m guessing the AMC has the bolts a little further apart. I can NEVER get that gasket to seal. I have run a file across the gasket surfaces to ensure the are clean and level, used a bead of RTV, no luck.

I can’t imagine as popular as the Chevy engine is that manufactures would compromise their product to save a buck, but the influence of bean counters is probably pretty significant.

 

[QBuff02]

To my amazement, manager dude held a vacuum cleaner over the oil fill in the freaking valve cover ! and I was able to change that gasket, with the crankcase full of oil and not leak a drop.

It works surprisingly well! Lol In the heavy equipment world we use actual venturi vacuum devices for making repairs from time to time. You can put them on any "compartment" that holds oil to replace blown O-rings and failed lines, piping, etc. This is one I have for working on hydraulic systems. Screw it onto the hydraulic tank fill, hook up your air line and let it do it's thing. I've pulled off 1" hydraulic lines to replace O-rings and complete lines and it just sits there on one end "gurgling" air while you do your thing. Saves so much time over having to pull the line, cap the component, make the repair, uncap it and install a new part and then clean up your mess when done. Or drain the system down enough to facilitate the repair and then have to refill it. They're a huge time saver.

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[Frankenchevy]

Why isn’t draining a gallon or so through the petcock and pouring it back in the simplest option?

 

[Chevyguy]

Why isn’t draining a gallon or so through the petcock and pouring it back in the simplest option?

Usually it is alot less than a gallon. I use this method and just top it off with fresh full concentrate coolant and water.

Clayton

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[Chevyguy]

Drain the coolant, remove the upper hose, thermostat housing and thermostat. Clean the mating surface and the manifold mating surface with a gasket scraper or razorblade. Wipe the surface clean with acetone or alcohol. Put a light coat of rtv on both sides of the gasket. Don't make a bead, spread it paper thin with your finger. Position the gasket on the manifold. The rtv will hold it in place. Install thermostat making sure it's centered in the opening. There is usually a small recess that it sits in. If it's not centered it will leak like you described. Install bolts making sure they not bottoming out before the gasket is clamped tight. Usually, one of the holes is blind and the other goes into the water jacket. Confirm this and use thread sealer on the bolt threads. Wait an hour to be safe and refill the coolant.
This is as step by step as you can get. Do it once and be done with it. Done this a million times myself, never an issue... except, with the POS o-ring housings that I refuse to use anymore for the exact reason. They rarely seal properly. Go get em tiger.

The aluminum housings have a habit of warping which causes leakage that sometimes the silicone doesn't seal. I sand the housing gasket surface on a piece of sandpaper that is on a true flat surface like a mirror or a piece of glass. A granite countertop will work too. Sand until the whole mating surface of the housing is shiny and clean. Wipe it off and then put it back on your intake with your new thermostat.

Clayton

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[80BrownK10]

Why isn’t draining a gallon or so through the petcock and pouring it back in the simplest option?

If it was me , well first I wouldn't keep contemplating it, but my petcock drains all over the dirty frame and spring and goes into the bucket really dirty. The time to stain it's not worth it. That said I would just pull it and replace what I lost.

Do y'all's petcocks drain into a bucket clear without hitting something? I have tried everything, from useing a hose to a funnel and nothing works very well. Maybe if I have a correct size flexible funnel and or cardboard bent just right I could make it work. But it's either such a small amount I don't care if I loose it or it's all getting changed anyway.

 

[Chevyguy]

If it was me , well first I wouldn't keep contemplating it, but my petcock drains all over the dirty frame and spring and goes into the bucket really dirty. The time to stain it's not worth it. That said I would just pull it and replace what I lost.

Do y'all's petcocks draw n into a bucket clear without hitting something? I have tried everything, from useing a hose to a funnel and nothing works very well. Maybe if I have a correct size flexible funnel and or cardboard bent just right I could make it work. But it's either such a small amount I don't care if I loose it or it's all getting changed anyway.

Mine hit's the frame too on my 87 V-20.

Clayton

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[Frankenchevy]

If it was me , well first I wouldn't keep contemplating it, but my petcock drains all over the dirty frame and spring and goes into the bucket really dirty. The time to stain it's not worth it. That said I would just pull it and replace what I lost.

Do y'all's petcocks draw n into a bucket clear without hitting something? I have tried everything, from useing a hose to a funnel and nothing works very well. Maybe if I have a correct size flexible funnel and or cardboard bent just right I could make it work. But it's either such a small amount I don't care if I loose it or it's all getting changed anyway.

There’s no dirt on my frame lol, but you’re right...it does hit the frame if you don’t use anything. I used a large tube that fits over the whole lever and rotate it until it starts dribbling out. Recently did this to install the coolant level sensor in the radiator.