What am I missing? Custom Cruiser Cooling Cystem Chapter

Car is my wagon, TBI 350. I assumed that the current thermostat was failed open, as the car really never registered over 160, so yesterday I set about replacing it. Purchased a 195 degree, as per the car's specs. Upon taking out the old one, I noticed that a PO had drilled a hole in the old thermostat, thus causing the running cold problem. I installed the new one and foolishly did not idle it in the driveway before taking off on a trip. About 5 miles in, the temp gauge got near 220, but it kept on going. I was able to safely pull over and shut it down as it hit 260. Car was audibly and visibly hot, so I waited until it was cool enough to drive home. Temps starting climbing again on the way home, too. Fearing a failed closed stat, I reinstalled the original one, and the car once again ran cold. So I exchanged the new one, and tested out the replacement using the hot water method. It opened as it should have. Installed that, reburped the system, and this time idled it in the driveway. 20 minutes later, same issue. I left the cap off and noticed when the stat opened up, but the temps kept climbing.

I replaced the gasket; hoses check out; water pump has to be working, as it would have overheated even with the drilled out stat; fan is always on

What am I missing here?

Sometimes the hole in the t-stat is to assist bleeding. Do you have a bleed procedure? I'm not familiar with that engine.

Drill a 1/16" (no bigger) hole in the t-stat. It's not enough to make it run cold or even noticeably delay warmup, but it'll make the system easier to bleed if the t-stat doesn't have a bleeding provision already. And it'll make sure there's a tiny bit of coolant flow past the t-stat pellet, preventing it from ending up in an air pocket or cold spot that makes it stick closed until everything heat soaks.

Got the copper bead/hole at the top? Next id check to make sure the radiator wasnt partially plugged. and make sure your radiator cap is okay

Wasn't there some old wive's tale about using an aspirin to wedge the thermostat open for a while to bleed the system, which would eventually dissolve and then let it close?

Suspect plugged radiator, water jacket full of rust, something like that, time for a really good flush(pull all hoses and block drains, blast every way imaginable with garden hose, then do the chemical flush).

Tough one. I'm thinking it's more likely a bleeding problem than a blocked radiator. If the radiator were blocked enough that it can't keep temps under control at idle, it would've caused overheating under heavy load even if there were no thermostat. So +1 for drilling a tiny hole. Some thermostats come with one from the factory.

BTW are the fans wired to be on all the time, or is there a temperature-triggered switch? If they're on a temp switch, that also indicates air in the system, maybe the fan switch is getting the hot coolant but it isn't getting to the radiator.

Fan is always on, even when the car is cold. What's tripping me up is that the car runs fine (too cold, actually,) with the original t-stat in place, which has been there for close to 10k miles under my watch, all in warm weather and on long trips with the AC on.

I've watched numerous videos on the tubes of you pertaining to TBI 350s and in none of them do they mentioned the system needing bled, but like I said, I did run it with the radiator cap off in an attempt to purge any air.

If no air can get past the t-stat, it'll never bleed, even with the cap off. The air stays trapped in the block / heads / heater circuit and makes an air pocket under the t-stat. Being in the air pocket, the t-stat doesn't open, so the air never leaves. A tiny bleed hole to let the air out usually fixes this, as the air can make it out to the radiator.

A lot of thermostats have a small bleed valve in them for this purpose, but I've seen a few cases where a hole was still needed.

I was starting in the same camp as the others that a small hole would be good for assisting bleeding, but the OP said he noticed that the thermostat did in fact open when the new one was tested so bleeding issues seem like they should have begun to self correct at opening. If everything works with the old thermostat perhaps you can try a new one with a lower opening point than 195? Say start at 175 and see what happens? Maybe by the time the 195 one opens the motor is just too heat soaked to recover. And like everyone has said. Put a small bleed hole in. It really does help.

Karacticus wrote: Wasn't there some old wive's tale about using an aspirin to wedge the thermostat open for a while to bleed the system, which would eventually dissolve and then let it close?

Not a wive's tale. I worked in a Buick/ GMC dealership in the early 90's. Every mechanic kept a bottle of aspirin in their tool box for exactly that. It works. We always used two aspirin though, 180 degrees apart to keep from cocking the center pintle on the thermostat.

As an alternative, you can always leave the thermostat out and water neck off and slowly fill the radiator until the level rises to the top of the intake manifold. When it gets up to the rim, drop thermostat in place and reinstall water neck. That will get them pretty much bled.

In reply to Cousin_Eddie:

I can certainly try the aspirin trick, but I should note that every time I installed a t-stat, the coolant level was right to the top of the manifold.

When that doesnt work do a radiator flush, at least the redneck way with vinegar and then back purge the rad and block with a garden hose on full blast

itsarebuild wrote: I was starting in the same camp as the others that a small hole would be good for assisting bleeding, but the OP said he noticed that the thermostat did in fact open when the new one was tested so bleeding issues seem like they should have begun to self correct at opening. If everything works with the old thermostat perhaps you can try a new one with a lower opening point than 195? Say start at 175 and see what happens? Maybe by the time the 195 one opens the motor is just too heat soaked to recover.

Right, it probably isn't an air issue if the stat cycled, not that a SBC is known for burping issues to begin with, being an engine that predates overflow jugs.

If 195 is heat soaking it beyond control, there's something wrong, plugged up somewhere, bad pump impeller, something to that effect. Which reminds me, the best way to really blast a water jacket out is to pop the water pump off.

Cousin_Eddie wrote:

Karacticus wrote: Wasn't there some old wive's tale about using an aspirin to wedge the thermostat open for a while to bleed the system, which would eventually dissolve and then let it close?

Not a wive's tale. I worked in a Buick/ GMC dealership in the early 90's. Every mechanic kept a bottle of aspirin in their tool box for exactly that. It works. We always used two aspirin though, 180 degrees apart to keep from cocking the center pintle on the thermostat. As an alternative, you can always leave the thermostat out and water neck off and slowly fill the radiator until the level rises to the top of the intake manifold. When it gets up to the rim, drop thermostat in place and reinstall water neck. That will get them pretty much bled.

most of my toys over the years have had a small block Chevy engine in them... the best way to bleed the air out of the system is to fill the coolant with the thermostat housing off, put the thermostat in and bolt the housing down and hook the hose up, then fill the radiator whole squeezing and releasing the upper radiator hose to fill it up. do that, and there is nowhere for air to be in the system at all. if you want to get really thorough, you can take the heater hose that is highest up on the firewall off and fill the system there with a funnel, but i wouldn't want to do that on a 90's B body due to the cowl hanging over the engine like that. i think (but not sure) that the heater hose that goes into the radiator by the fill neck is the higher hose, so you could unhook it there and use a funnel to fill the system with the radiator cap on until it comes out the bung in the tank, then jamming the hose back on.

you can also get it pretty much fully bled if the upper rad hose and thermostat are in place by taking the temp sender next to the thermostat housing out and filling it until coolant comes out, putting it back in, and squeezing/releasing the upper rad hose as you fill the radiator.

You should supercharge it. Im not sure it will solve the cooling issue, but it will be faster.

So I re-re-installed the original t-stat, making sure I did nothing special, and then drove it 30 miles into town with the AC on. The temp never even reached 160, which was never really uncommon. Who knew a $3 part could cause such a kerfuffle?

Wait a minute... This sounds vaguely similar to a quirk I had on the Jeep after I restricted the water pump bypass. After that, the flow through the bypass and heater circuit was pretty even, so there was basically no flow past the t-stat until it opened. With it in that cold spot, the temps would climb to 230 or so with the t-stat closed. Then, the t-stat would get warm enough to open and it would drop to 190 and cool normally for the rest of the drive. A 1/16" hole in the t-stat got just enough flow past it to prevent the cold pocket and solved the issue.

There's definitely something up with the t-stat setup. Either the new stats aren't opening enough or something. Is the water flow area that opens the same size as the old stat or is it smaller? If the new one is a stant superstat, toss it and try something different. Those seem to have a small opening area and have caused some weird cooling quirks for me. The ACDelco (rebranded Motorad) high flows seem to work well.