thermostat not opening? HELP ASAP

[Squareforceone]

Hey all i'm really worried about my 84 with a 350. the thermostat doesn't seem to be opening. I ran it without the thermostat for a bit to tune and adjust timing and stuff (motor swap) and never had the temp light (idiot lights) come on. Well today i put in a new thermostat with the spring going into the engine and let it run for a few minutes with the heat on and the raditor cap off to try and bleed the system of air. Well the the upper hose never got hot. the heater hoses and bottom rad hose did and after a few minutes the temp light came on.... please help i need to go out of town in the morning

[bilfman]

You can drill a small 1/8 inch hole on the side of the t stat. Just make sure to drill where it is flat metal and does not interfere with any of the stat mechanics, this will allow air to bleed off if that is your problem. That is an easy start to see if that is the issue.

[Squareforceone]

I've heard that before, i just hate to waste more coolant/another gasket. could having the rad cap off cause this?

[bilfman]

Drain and save the coolant. And just use the same gasket with a thin layer of auto silicone. A new installed gasket will come off easy. No waste there of anything.

[Squareforceone]

it's rtv'd in place

[Slammed84]

Stupid question, do you have enough coolant? You chan check the thermostat ib some boiling water to see if it opens.

[BADAZ chevy guy]

It could be that you got a defective thermostat from the store. Like my dad use to say "New doesn't mean good... it means Shiny!"

[willett]

Or you bunged it up with RTV. Stranger things have happened.

It's not difficult to install a t stat upside down either.

[Squareforceone]

i don't think it was upside down the spring was in the intake is that correct? I mean yeah i suppose it could be bad but i really am hoping/thinking that's not the problem here.

[Squareforceone]

also i didn't drain the coolant i just took off the upper rad hose and then topped off the system afterwards

[Tx Firefighter]

For others that may be dealing with this in the future.

Here is a picture of the vent holes the above poster mentioned. Just use a little drill bit.



A good gasket to use. It's reusable and never needs silicone or any other form of sealer. You can buy them at most any parts store, but you'll likely need to tell them the part number because it's not a hot seller since it costs more than the thin paper ones.



It's much thicker than the cheapies.





Just drop it in place dry and install your housing.



If in the future you need to remove the thermostat for any reason, you can reuse the gasket again without any worries.

[russgt]

+1 on above, excellent write up. The hole trick works great, but make sure you didnt put the t-stat in upside down, I have seen that before.

[Tx Firefighter]

And, for goodness sake, use anti-seize on the bolts.



Guys who don't use anti-seize on thermostat housing bolts are often the guys who start threads like "help, I've got a broke off bolt in my intake" often followed by mis-guided advice with threads like "help, I've got a broken off eze-out on my intake".

But, that's a whole other thread topic.

[BADAZ chevy guy]

Originally Posted by Tx Firefighter

Guys who don't use anti-seize on thermostat housing bolts are often the guys who start threads like "help, I've got a broke off bolt in my intake" often followed by mis-guided advice with threads like "help, I've got a broken off eze-out on my intake".

So true... so true. Been there, done that

[Keith Seymore]

Good write up, TX.

I have also heard of guys using an aspirin or two to hold the thermostat open during initial use (until the coolant is circulated and the aspirin disolved).

K

[Squareforceone]

I'M GOING TO BURN THIS PILE TO THE GROUND. I NEVER had an over heating problem with the old motor.. now nothing but over heats it over heats after like ten minutes of driving. drilled the hole in the t-stat also did the boiling water got the thermostat to work just fine.. so i take it to the tranny shop to get my tv cable looked at. Take it on a test drive with the guy the damn thing over heats. Take back to tranny shop guy thinks its the fan clutch. So i drop 55 bucks on a fan clutch. take it for a ten minute drive and the temp light comes on.... wtf it's got a new fan clutch a new t-stat all new hoses, and the water pump is circulating.. what else could it be i've never had a problem with the rad before.. could my coolant mix have too much water? Is it something major like a crack in the block or something. if so how do i check.

[Tx Firefighter]

So its full of coolant, the thermostat is known good, and the coolant is circulating.

How do you know it's not the temp light itself that's bad ? You might be chasing your tail trying to fix something that's not actually broken. What clues other than the temp light do you have that leads you to believe its overheating ?

[bilfman]

Could also be a timing issue, timed like s$it could cause an overheat.

[Squareforceone]

and now a new a rad cap... thats it's got to be a f***king cracked block. I'm so pissed right now. can a compression test see if theres a cracked block

[Squareforceone]

if the timing was that far off would it cause it overheat that fast. and when it over heated on the test drive from tranny shop it was hard to start back up....

[buddy_1]

You said engine swap in original post. Was the engine new, used or rebuilt? If used, what year model did it come out of? Buddy

[71swb4x4]

Buy a temperature gauge so you know for sure what is going on. If you aren't willing to do that make sure the temperature sensor is good.

[Squareforceone]

okay what's the 100 percent right way to install this thing i pulled it out and run without a t-stat and now it's not overheating at all..

[Tx Firefighter]

You're getting frustrated and not thinking clearly.

With the thermostat out and the water neck off, fill the radiator until the coolant level is just at the bottom of the cavity where the thermostat goes in the block. Do it slow, let it slowly rise. It might take a few minutes until the coolant rises and stabilizes.

Install thermostat like my picture above. The spring goes inward, out of sight. Then install water neck without upper hose in place. Now, slowly add coolant until the coolant is right at the top of the water neck and about to spill out. This may take a while and/or a few fill and wait cycles. What you're doing is adding coolant and letting the air burp through the little holes in the thermostat. When you see water above the thermostat and ready to spill out, you've accomplished that. Take your time. Let it burp a few minutes, top it up again, etc until it doesn't burp anymore.

Now install upper radiator hose and fill radiator completely.

Fill overflow bottle to the line

Start and run engine and warm it fully.

Report back...

[Rubble]

Originally Posted by 71swb4x4

Buy a temperature gauge so you know for sure what is going on. If you aren't willing to do that make sure the temperature sensor is good.

At least get hold of some sort of temp gun,shoot your temps on both sides of T stat. It's possible you have a bad sender.