The Stovebolt Site Forums The Shop Area General Truck Talk Trapped air...confused?

OK....now you have done it confused me yet again and that is easy to do.....OK, coolant drain plug for engine on driverside lower corner of block.. open and flush engine/radiator.. install new hoses and new thermo...add coolant and make sure heater core valve is open...fill with coolant and let her warm up and keep filling her.....where is the air...the air is pushed out via the top of the radiator says my cousin the mechanic. I want to drill small hole in thermo but Mr. mechanic says NO not nessasary! I want to keep truck slight up hill while filling... Mr. mechanic says no not necessary......I GIVE UP...what is the correct coolant filling procedure step- by- step ? I trust you guys more than Mr.(my cousin) the Mechanic....t/c steve :confused_smile: :mad:

Steve don't be confused,be deffused !! The radiator should be your highest point.As you run the engine and the water pump circulates the coolant, it should bring all of the air to the top of the radiator.As a side note,Oldsmobile used a thermostat that had a small hole in it for years.
May all your air disseminate !

Well, it can't be that easy....if the thermo is working why would you need a hole in it ask my cousin Mr. Mechanic...he has me there. I need a good answer gtow69....T/C Steve

Steve,

Under the perfect scenario, a large air bubble would find the highest point in the engine to roost...this would be immediately under the thermostat. The little thermo-motor needs direct contact with heated coolant to react properly.

The small hole that is drilled in the flange allows this bubble to travel through to the tank, along with a limited flow of coolant, but insures the thermostat is surrounded by coolant.

This is how I envision it working, but between the Zanax and the Cutty Sark, I might be in Belfed's fog zone! :confused_smile:

Stuart

The hole in the therm. is agood idea. I usually pull the heater hose off right under the therm & fill it till it comes out of there & shove it back on, then continue filling. Running the engine till the therm. opens & then filling is not a good idea especially on the newer engines. A dry hot spot can crack or warp a head.

Someone once suggested wedging an aspirin in the stat to help purge the air. Of course I read that after I had already drilled a hole in mine. Stovebolts are notorious for trapping air in the head.

Curt B.

Why do you think the factory installed a steam vent in the 261 block and head?

If all else fails you can take the aspirin with a glass of water.

And if things are still hopeless, that another aspirin with a glass of coolant!

Stuart

OK guys keep your day jobs the comedy act still needs work.(:>)... I will drill a hole in the stat and fill the hose below the stat. What else can I do to insure a good job and a happy 235. What would be the best type of coolant/mixture for this engine and will a 165 degree stat do the job with a four pound cap on a 55- 57 235 engine....THANKS, Steve

50/50 regular old green stuff. Don't use the pink/orange or the gold, those are for late models and can damage the pump. The "mix with anything" will be fine, too. If you can find it, get the full strength stuff and cut it yourself. I find that the "pre-mix" is a little weak for my tastes.
Side note, I didn't drill a releif hole in my theremostat, and have had no issues with air in the block/head, however, it won't hurt anything to do so. There are even thermostats on the market that have a hole already in them.
one more thing-pour it slow. Don't rush it, just go nuce and easy. That will help allow the air to purge out. If you listen to it, you should be able to hear the air comming out at the filler neck.

THANKS BILL...where might I go to purchase one of these stats with a pre-made hole and what do I ask for? Is 165 a good number.. it gets a little warm where we are in the summer 88-98 and gets to 32 to 48 average in winter...T/C, Steve

165 is waht they came with factory, I'm running one myself with no overheating issues. I'll have to check on who actually make those thermostats, but i know i've seen them, maybe at Napa?

Bill,
when/if you find out where they can be purchased please let us know. There are several owners that have never heard of the hole/vent on a bolt stat. We are all interested...we are still learning about these bolts. Thanks and T/C Steve

I'm not having luck finding them online, I can't remember who makes them, but i know I've seen them. Next time I'm at the flaps or the speed shop, I'll look into it.

You can just loosen the coolant temp sensor to let the air out of the head, but the hole in the stat is nice if you suddenly suck air and don't realize it.

A lot of times you can get away without the hole if the stat doesn't sit tightly in the housing- it might leak a bit.

The BMW I used to have had a bleed screw on the thermostat housing that worked nice.

The 261 doesn't need a hole in the thermostat if it has a bypass thermostat, the bypass takes care of the air burp.

The only thermostat I've ever seen that had a factory burp hole was a Robertshaw thermostat, and I haven't seen a new one anywhere, the only ones I can ever find are Stant.

Hi Steve; I had to replace a faulty thermo. in ol' green just last week. I got a 185 from NAPA but I'd go with a 165 since your weather tends to be on the warm side. I drilled a 1/8" hole in the flat spot of the thermo. Took all of 15 seconds if you don't count the time lost trying to locate the drill bit in what has to be the world's messiest shop. (I cleaned it up since then, now I probably won't be able to find anything)

She burped herself (the truck) - no problems at all.

the reason you want a couple holes drilled in the edge of your thermastate is a good one it will save your engine when the thremastate sticks trust me it does happen i wont run one without a few holes in the edge after overheating two engines over the years one 68 chevy one new boat with a chevy 4 banger that ran just hot enuff to burn the head up after a year the guage never went over 190 it always ran just a little hot runs perfect now and yes the therm. is drilled

32fire2
Question: What size hole are we talking about? If it would save overheating when the thermostat locks up I would think it needed to be 1/4".

The hole in the thermostat is great for removing air from the system however if you want to prevent damage when the thermostat fails get one of the new ones that fail in the open not closed position. These things are a life and an engine saver.

1/8" or 3/16" will work fine. I drilled mine based upon advice received from a lot of 'Bolters. No problems. Think the original early thermostats were two stage and were manufactured by Harrison who also made radiators. Don't know exactly how they worked though. Mine's a Stant.

http://community.webshots.com/user/geezer

I'm back t/c Steve.Got no GOOD answers, just ones that seem to work.The hole in the thermostat will purge the air out even when the stat is closed (as in when it sits overnight).Usually you can hear air in a system at the heater core.

haven't had a chance to check on that thermostat yet, I know someone still makes them, might have to look in some of my catalogs.
If you're concerned about the 'stat sticking shut, you might consider the Motor-Rad theremostat. They're not supposed to stick in the closed position.
One more suggestion, not really on purging, but I would suggest a bottle of Red Lines Water Wetter. I use it in mine, and it does make a difference in the effficiency of the coolant.