You need to get an overflow bottle on the radiator and make sure you have the correct cap for a recovery type system. A 13lb cap should be correct but someone else may have a better idea on that. You need to keep the cooling system closed to accurately diagnose your problems. Having the system open to look at coolant flow only allows air into the system which may compound your problem. You say it takes longer to heat up if the heater is on? That tells you that your current cooling system in not up to par. The heater acts like a second radiator helping to cool the engine. I think you said that the radiator you have was flushed and rodded correct? I saw that someone said to check your lower radiator hose as well. This is a good idea as the cheap hoses that dont have a spring in the will collapse and restrict waterflow. Just more food for thought. Hope I helped.

There are some tech articles here that may or may not help:

http://www.arrowheadradiator.com

The thermostat is in correctly, and the onley way I can think of to make sure that it is a standard flow pump is to pull it back off and pull the back off of it.... The water is flowing through the thermostat and across the top of the radiator when the thermostat opens I watch this with my own eyes.... but would it still flow this direction from pressure even with a reverse pump? at this point I am frustrated as hell and need to just step away from it before I start using a bigger hammer....

I doubt you have a water pump problem. Let’s go back to your carb. When you tuned it, did you use a vacuum gauge? In addition, if have an automatic transmission did you tune it in drive with emergency brake applied and wheels secured? You may be running too lean.

No crime in that.

If you can beg, borrow or steal a non-contact thermometer you can chase the different temps around the cooling system and compare on the head at your mechanical temp gauge sensor. Also, it does less damage than a bigger hammer.

You'll get it. We're plugging for ya.

All i have done for tuning is adjust the idle mixture... I have not done anything with metering rods or anything like that.... I adjusted the idle mixture screws in one side at a time untill it caused the idle to get ruff then backed them out untill the idle reached max idle then gave one more full turn out.... This is a 600 cfm edelbrock performer....

Just pulled this from Edelbrock Performer Series tech page. It appears from your discription you didn't tune properly. Here's the link

The Edelbrock Performer Series carburetor has conventional Idle Mixture
Screws (IMS) that provide a leaner A/F when turned clockwise and richer
A/F when turned counter clockwise. The idle air flow is controlled by a
conventional screw that opens the Primary Throttles. The following
procedure should be used to set the idle mixture and speeds:
1. Fully warm engine and ensure choke is fully open.
2. Air cleaner in place.
3. Set desired speed with the air screw.
4. Adjust the IMS on ONE side to get the maximum possible RPM. Do
not go rich beyond the maximum speed point.
5. If the above changed the idle speed more than 40 RPM, then
re-adjust the speed.
6. Adjust the side OPPOSITE of that in Step 4 to get maximum RPM.
7. Reset the speed.
8. Carefully trim each IMS to again get the maximum idle RPM.
9. Go leaner just enough to get a 20 RPM drop in speed.
10. Reset the speed to the desired RPM.
11. This is a Lean-Best Idle Set. Setting richer than this will not
improve idle quality or performance, but could tend to foul spark
plugs.

WINTER FUEL IDLE SETS
During the winter months (in most parts of the country) the local fuel will
be a “winter” blend that is very volatile, as an assist to cold-engine
starting and driveability during warm-up. However, the high volatility has
the disadvantage of allowing excessive vaporization of the fuel if the
vehicle is operated in a heated area such as a garage. This can result in
problems in the idle-set procedures since the carburetor’s internal vents
will allow this excess vapor to be drawn into the throats and enrichen the
mixture. The idle will be erratic and not seem to be able to hold a set.
To resolve this type of problem, it is advisable to perform the final
settings outdoors after the vehicle has been stabilized with a drive of
several miles.

CALIBRATING THE ACCELERATOR PUMP
If you encounter any hesitations or stumbles that do not seem to be
related to the basic metering or have not responded to changes in the
basic metering, move the pump drive link to one of the holes closer to
the carburetor body. This will increase the stroke length of the plunger
and result in more pump delivery.

FLOAT ADJUSTMENT
To properly adjust the floats in the EPS carburetor, two procedures must
be followed. First, the metering rod/power piston assemblies should be
removed from the top of the carb airhorn. Next, remove the accelerator
pump connecting rod and the choke connec-ting rod. After removing all
the airhorn retaining screws, turn the airhorn upside down with the
gasket in place (See Figure 3). Use a scale, or a 7/16" drill bit (as
shown) to mea-sure the float level. There should be 7/16" between the
air-horn gasket and the top of the outer end of the float. To adjust the
float level, bend the float lever until the recommended level is attained.
DO NOT press the needle into the seat when adjusting the float lever.
Next, you should check the float drop (See Figure 4). Hold the airhorn
upright and let the floats hang down. There should be 1-1/4" ± 1/4"
between the airhorn gasket and the top of the outer end of the float. To
adjust the float drop, bend the tab on the back until the recommended
float drop is attained.
3. Connect all throttle and transmission linkages and throttle return
springs.
CAUTION: At this point, make sure all throttle and transmission
linkages operate smoothly from idle to wide open throttle (WOT)
and check return springs for proper pressure.
4. Connect all vacuum hoses to their proper location on carburetor
(See Figure 1). Replace hoses that appear brittle or cracked.
5. Connect fuel line to carburetor (See Figure 1). Avoid contact with
any sharp edges or areas of extreme heat. For best results, use
Edelbrock in-line fuel filter #8873 and fuel line kit #8135.
6. Install new air horn gasket and air cleaner stud (supplied). Install
air cleaner making sure it does not contact linkage or fuel line and
has proper hood clearance. Extremely low profile air cleaners will
not fit without #8092 (due to choke interference).
7. Trim air cleaner stud to proper length.
8. Re-check all linkage for smooth throttle operation.
9. Start the engine and check for any possible fuel or vacuum leaks.
CAUTION: Be alert to carburetor flooding. Flooding can be caused
by dirt, small particles of hose cuttings, floats and inlet needles
which have settled during shipping. When the fuel pump is turned
on or when the engine is first started, watch closely for signs of
flooding. If flooding occurs turn engine off immediately and lightly
tap on the side of the carburetor that is flooding, in the rear needle
and seat area with a rawhide mallet or wooden handle of a
hammer. Start engine and see if flooding continues. If flooding
continues, stop the engine. Clean up any raw gasoline and refer to
the “Adjustments and Troubleshooting” section of the
Instruction Sheet.
WARNING: NEVER POUR FUEL DIRECTLY DOWN THE
CARBURETOR WHEN ATTEMPTING TO START THE ENGINE! THIS
MAY CAUSE A BACKFIRE AND POSSIBLE ENGINE
COMPARTMENT FIRE, RESULTING IN ENGINE OR VEHICLE
DAMAGE, PERSONAL INJURY AND/OR DEATH.
10. With engine at normal operating temperature and choke fully open,
set idle speed and mixture screws. This procedure is outlined in the
Instruction Sheet.

thanks for the info I will try that again in the morning.... the problem is that it is running hot going down the road and the IMS is just for the idle anything above idle is all on the metering rods..... its a long shot but I will adjust it out again tomorrow....

Your welcome, I think we could both use some rest. Goodnight.

The link above was not working, it can be seen HERE.

You suppose one intake gasket is positioned so that the open water port is in the back instead of the front on one side? I say only one, because you said there's flow from the water neck.

I would suspect the passenger side to be wrong, that would explain why running the heater helps, this would allow flow through the bypass on that side.

Thanks for the heads up on the link. It's fixed now. Sorry about that folks.

AFA whether the pump is the correct rotation, a recent THREAD here on this forum has a photo I took of a standard rotation water pump w/the back plate removed.

The thread also has a lot of discussion on various overheating solutions.

I'd be very interested in whether you find a solution, since I've had similar problems with the GMPP 290 HP 350 in my pickup.

My truck runs the temp up to the thermostat setting (195 high flow) fairly quickly, and then stabilizes at about 200-205 if I run at speeds up to about 40 mph. However, if I run at highway speeds the temp creeps up to about 225, and then spikes to about 230 when I come to a stop. It doesn't throw any coolant or steam out, but I don't know why it runs so hot. I'm afraid to run the A/C because I think it may overheat.

One of the significant differences I have compared to your vehicle, is that I'm using the original 1975 GMC pickup setup for HD cooling in my 3/4 ton truck (3 row rad, HD clutch fan, full shroud, CW waterpump, etc.) so I assume the original design should be adequate. This truck cooling system was designed to handle a camper load of up to 2600 lbs, and I'm running it empty. It should not have an overheating problem.

When I put this engine in I replaced all cooling parts except the stock steel 7 blade fan. I have checked the fan and its mounted correctly. I have the heater and all other stock parts installed, including a 14 lb cap. I am running an Edelbrock Performer EPS manifold and 1406 carburetor. Initial advance is about 12 degrees, with another 20 of mechanical. I am using manifold vacuum, and the vacuum advance runs about 18 degrees.

Some ideas for what I am going to check.
- Verify TDC manually - the balancer and pointer were new, but maybe they are off
- Resolve a very minor (and intermittant) coolant leak where the upper hose connects to the water neck - maybe I am losing pressure
- Use an infrared thermometer to verify the inlet and outlet radiator temps - maybe the stock 3 row is not doing its job
- Try advancing the initial timing further - with my 222/222 cam, it may work better to have more initial timing.
- Find another stock vehicle and try to figure out if there is something wrong with the radiator air flow - There was no stock air dam under the bumper in 1975, but there may have been a dam that ran from the grill to the radiator bottom to direct more air through the radiator. I have seen this arrangement on newer trucks.
- Switch to a 4 row radiator - they are harder to find and more expensive, but were a typical option for the 454 and diesel trucks

I'll keep monitoring the thread, and let you know if I am able to figure out anything useful.

Bruce

and minor blown head gasket. And to troubleshoot by checking compression and spark plugs.

That's kinda easy to do without a big spread of time and money.

Gotta go.