I just bypass the heater core, i plugged the intake , water pump & heater hoses. Now the temp gauge is all over the place. I topped off the intake before i plugged it. No leaks ! Do i have an air pocket? By the way it's a '73 with a 350 with vortec heads, automatic & tauras fan.



Thanx !

 

Is the rad full? Coolant recovery system in place and functional?

 

yes.............it's not getting hot, guage just goes way up and then back to normal.

 

Don't plug things up as you have. Run a hose from the water pump to the intake manifold to allow circulation. Yes I know it's 5/8" at one end vs 3/4" as the other but worm clamps can do wonders.

 

Sticky thermostat.

 

Well I don't know but it is a potential $10.00 solution.

 

I plugged off my heater ports years ago and never had a single problem. You will get flow through the manifold with or without that path. Closing off one port just means more flow through the other(s).

The sort of fluctuation the OP is talking about would either point to an air pocket which in all likelihood would've cleared itself after the first drive, or a sticking thermostat as Mike mentioned.

 

One other remote possibilty is that the water pump bypass has been plugged or a water pump without one has been installed AND you have a tstat without bypass holes.
This will cause the coolant to reach a higher than normal temp before the tstat opens since there is essentially no flow by it.

I too, have the water pump and manifold ports plugged up, but also no internal pump bypass, but use a tstat with bypass holes with no issues.

 

I had no problem before i did the bypass ......this is the first time i drove it. The plug i used for the water pump went in a little far, but not enough to block anything. I MAY PUT IT BACK THE WAY IT WAS, JUST TRYING TO GET A LITTLE HEAT OUT OF THE CABIN !

 

Ok, before you do anything else, let the engine cool completely down, top off your rad and go for another drive. See if it happens again.

By pulling those hoses loose, you introduced air into the system. It's very possible that you were just seeing the effects of that air pocket working its way through.

 

I did that.................same thing ! I guess it's time for new thermostat. May just be a coincidence the thermostat took a dump the same time i decided to do the bypass.......Always something, but my motto is...Don't sweat the small **** ! !

 

I'm surprised the overnight burp didnt work. Air can be stubborn and the heater does help with that,try drilling a couple holes in your old therm and see if that fixes it.
And don't discount what Noonie said about the bypass being plugged,some people feel compelled to install that little plug in that little hole when the unpackage their rebuilt water pump. Most actually have no idea its there. I've even opened rebuilts that someone has already stuck the plug in the hole.

 

Yes Sir; I installed two valves in the heater lines, when I turn them off, I experience the same problem. My Auxiliary fan kicks in & it cools right off, so I know it is above the factory set 230 degrees. I did install a new Thermostat, but to no change. Each time I go out this happens. When I open the valves for winter heat, it eliminates the problem. I have not heard about the Thermostat with built-in holes. Could someone give me a number for this. Note; The engine is not boiling over, so I'm not really worried about it. But I would just as soon know the reason. Typical Corvette Owner, LOL Have a great day. Gene

 

As you know, in Florida we can do that for a little better cooling performance, in my case the Stewart pump doesn’t have the hole in the casting at all. Have run into the plug installed several times too.

Here is a pic of a common tstat, you can see the oem hole and the added hole. The added hole only need be 1/16” if at all. Check for the hole, most have it, some don’t.



With the tiny oem hole and an empty engine, it may take 10 minutes for the bubbles to work thru the hole when filling, most people don’t wait that long and end up with the air pocket.

The other common problem is that people take it for the first ride and remove the radiator cap after they return.
Once you top off the rad initially when warm, you don’t remove the cap again. That will break the cycle. Any addition of coolant should be done at the overflow. You can tell by the level in the tank, if the system has taken more coolant, thus purged air.

Generally a litttle hole in the tstat will help circulate heated coolant past the wax pellet a little faster than not in that area and the tstat should open before the engine gets any local hot spots.

Now in the rare case that you are running a water pump with the bypass closed off, then a balanced tstat is recommended that has at least 3 1/8" holes. Prevents local hot spots and possible damage. Available from Stewart Components.

 

I had the same issue with my car when I attempted to bypass the heater core. I plugged the intake manifold and the water pump. The car would not run as cool as it did before and the temperature spiked a lot. I did have a stage two stewart warner high flow water pump AND the modified thermostat (three holes drilled) and it still did it. I ended up just running a hose and the problem disappeared immediately.

I can't explain it!

just my $.02

 

Many C3s came from the factory with a shutoff valve, and many more members (like me) have added one.

A shutoff valve achieves the same purpose as adding plugs. I don't understand why only a few cars see the weird temp spike.

 

I've installed one on just about every car I've owned including my C5.

Prob. because like Noonie said, if you stop the heater lines' flow AND you have a thermostat without the little hole through it then there isn't much flow past it. I can't remember the last time I saw a thermo without the hole in it, but I know they're out there.

 

Good call on the sticky thermostat ! I put on a new one and put (2) 3/16" holes in it, car runs cooler that ever ( so far ). Coincidence it went south when i installed the plugs !

 

I think I've found the solution to my heater bypass problem. I'm going to install a Chevy Astro bypass valve. It keeps the normal coolant flow but lets me bypass the heater core. I can control the valve from inside the car so I can de-ice the windshield on those frosty Florida mornings. OK, more like those thunderstorms that fog the windshield and the chilled air from the A/C just makes it worse. I thought about plumbing the vacuum line into the heat/AC system but couldn't figure out which line(s) to tee off.

I'm going to use the manual over-ride valve for the windshield wiper door (below the steering column). I have the long L-88 hood so the valve is disconnected. When my wife is in the car, I need to be able to adjust the temperature (she wears a sweater or jacket in the car even in the summer here in Florida - she likes the house at 80+). What I'd really like is a dual temp system so we could both be comfortable.

All four connections are 3/4-inch but I had no trouble getting the 5/8-inch hose connected. It'll be out of sight right next to the heater core connections