So what did you do to your GMC today?

[Richard RV]

Thermostat determines the lower running temp. An open thermostat is an open thermostat.

What keeps you from overheating is the fan clutch and radiator. And also engine tuning(correct timing, not leaned out, ect..).

Your description of your stalling issue in my opinion doesnt seem to be normal vapor lock issue. Vapor lock is usually easy to predict on gmc’s. At the temps your stalling out at, there is something else odd.

Yep. A stock GMC might run at ~195° regardless of the thermostat, and a coach with an aluminum radiator and upgraded fan might run at or below 180° regardless of the thermostat.

I agree that there's probably something else going on. My mantra - Just because you have one problem doesn't mean you don't have two.

It was good to rule out the fan clutch and continue following the diagnostic path.

 

[RvRev2]

Yep. A stock GMC might run at ~195° regardless of the thermostat, and a coach with an aluminum radiator and upgraded fan might run at or below 180° regardless of the thermostat.

I agree that there's probably something else going on. My mantra - Just because you have one problem doesn't mean you don't have two.

It was good to rule out the fan clutch and continue following the diagnostic path.

I'm thinking you are right. Something else is wrong. I took it for a spin today, and my secondaries are not opening. It also took forever for the engine to reach operating temperature. It was 85 degrees outside. Secondaries wouldn't open, and it stumbled on acceleration. Until I get this figured out, my rig isn't going anywhere.

 

[Bhart]

From: quadrajetpower.com

Secondaries won’t open

Symptom:Secondaries don’t open, press pedal to floor and they don’t move Solutions:
•Secondary air valves on top of carb won’t open unless under load. Revving engine in park , they may not open.
•Quadrajets have a secondary lock out system, most to hold throttle blades in base, some early 65-70 have it on the air horn to prevent air valves from opening. This is activated by choke. Make sure choke is completely off, and the lock out is clear of the throttle blades. These lockouts can be removed if desired.
•Check throttle cable to make sure it is adjusted correctly. With engine off, some body presses pedal to floor and make sure throttle blades are open fully.
•Make sure base gasket isn’t interfering with throttle operation

Lots of good info from this web site.

The throttle peddle can be twisted enough so that even if floored there is not enough cable pull to open the secondaries.
Emery Stora came up with a solution to use the large split shot (fishing gear) on the back side of throttle peddle along the cable to shorten the cable throw.
Maybe you can grab ahold of the throttle peddle and try to force it up a bit.

Post #2 from Matt Cole

Post in thread 'Add 30hp to your 455 for $2'

Jun 8, 2018

> Parameters in the title are very approximate but I will share my discovery and see how much more power you get out of your 455:
> I found my secondary throttle leaflets were not opening completely. When I went about trouble shooting this,among other issues, I found that the
> rubber grommet that connects the accelerator cable to the throttle carb linkage was worn through completely. This loss of an 1/8" space prevents
> the secondary leaflets from opening completely. I was able to get a replacement from Aplied GMC and now I have full opening of my secondaries and
> more power. Pretty...

• Matt Colie

 

[TC429]

took our 65 galaxie with the youngest son who graduates tomorrow, and a few friends in their 'senior parade' thru town, JUST after end of parade, freaking alternator went out- it was the original, guess 61 years later cant complain much...
made it home before it went dead, and loaded everyone int the GMC- took 9 kids and the dog to dairy queen, got food and went for a drive...lots of room, lots of laughs, it was kinda cool.
I did do the drivers side lower a arm bushings yesterday evening, took under 2 hours including gettin/putting away tools, feels less affected by bumps, im sure the old loose bushings were letting the wheels squirm all over the place. didnt notice as much difference, but changing the passenger side the other day was night and day... oddly felt about same after doing drivers side- but road crown/road edge might put a lot of different loads on them I guess...
Anyways was a fun little drive in the GMC, and on its 48th birthday according to the build sheet

 

[sailor man]

took our 65 galaxie with the youngest son who graduates tomorrow, and a few friends in their 'senior parade' thru town, JUST after end of parade, freaking alternator went out- it was the original, guess 61 years later cant complain much...
made it home before it went dead, and loaded everyone int the GMC- took 9 kids and the dog to dairy queen, got food and went for a drive...lots of room, lots of laughs, it was kinda cool.
I did do the drivers side lower a arm bushings yesterday evening, took under 2 hours including gettin/putting away tools, feels less affected by bumps, im sure the old loose bushings were letting the wheels squirm all over the place. didnt notice as much difference, but changing the passenger side the other day was night and day... oddly felt about same after doing drivers side- but road crown/road edge might put a lot of different loads on them I guess...
Anyways was a fun little drive in the GMC, and on its 48th birthday according to the build sheet

Good time to upgrade the alternator. This install has (2) Balmar alternators. The red one is a 12v 160a alternator. It is controlled by a WakeSpeed WS500 remote regulator which I have set the dip switches to reduce the output t0 120a.

At full put out, it will take 6hp to generate 160 amps. The reduction to a 120 amp put out only needs 4.5 hp.

These parasitic loads on the 455 are far greater with the original dumb alternator.

The metal colored alternator below is a 48v 60a alternator.

 

[sailor man]

We heard some tapping sounds from the valve train, so we took off the covers and ran the engine. Messy oily business.
We had to tune everything and some of the components were not securely fastened. In a couple of instances there was no oil coming through the lubricating jets.
Everything is good now & not taps.
Didn't know that some parts where not getting lubricated.
A future engine breakdown was avoided.
When bought from the COOP when the shut down auction was happening, I was told that this engine had been broken it by the COOP and was sitting on a shelf the I found it.
It has never been on th interstate.

We are having trouble holding the high fuel pressure needed for the FiTech fuel injection system. With all of the threaded connections, there are multiple location where there may not be a perfect seal. We are breaking everything down an installing fresh heavy blue Teflon tape.

We hope that this will connect the weaknesses in the system.