Overheating Rebuilt 350

[KDizzle]

Also... I went back to your first post and looked at the water pump you ordered. That water pump says it is a STANDARD rotation pump. If you go to 1992 instead, the C3500 only has that same pump listed as a GM option and it also states STANDARD rotation. When you go to a C1500, you have that as an option, but also have GM 252719, which says it is both taller and REVERSE rotation.

It appears you found the culprit…me, ordering a standard flow water pump. It most likely is a coolant flow issue based on whats happening and your keep observation. Much appreciated for catching that and suggestions on purchasing options. I’ll see what my options are between Local, Summit and RockAuto. Once I get the right parts and get it buttoned back up. I’ll give it another go and post results.

Really thankful for all the knowledge and experience on this forum.

Ricko1966, your original suspicions were correct!

 

[KDizzle]

Update:
New reverse water pump, reverse fan clutch and reverse fan installed. With front end lifted; using water; no thermostat; upper fan shroud installed and a fan blowing air in the front of radiator, I was still dealing with overheating, however, not as quick. Was able to finish break in. Motor sounds great. Now at idle, still dealing with running hot. Left radiator cap off during idle and tried to burp air out of coolant system as best I can while adding more water. Temp gauge still slowly climbs. After about 15 mins idling, I cut it off at a temp of about 230 (according to gauge). I’m guessing I need a temp gun to verify temp and then regroup.

Will using water instead of coolant and not having a thermostat installed contribute to running hot? I plan to drain and replace water with coolant, but only after I get it running at a decent temp.

Water circulation seems much better.

 

[Rustisbest]

Verify that the timing isnt retarded. Anywhere around 10 initial or so would be a good starting point.

 

[Bextreme04]

Update:
New reverse water pump, reverse fan clutch and reverse fan installed. With front end lifted; using water; no thermostat; upper fan shroud installed and a fan blowing air in the front of radiator, I was still dealing with overheating, however, not as quick. Was able to finish break in. Motor sounds great. Now at idle, still dealing with running hot. Left radiator cap off during idle and tried to burp air out of coolant system as best I can while adding more water. Temp gauge still slowly climbs. After about 15 mins idling, I cut it off at a temp of about 230 (according to gauge). I’m guessing I need a temp gun to verify temp and then regroup.

Will using water instead of coolant and not having a thermostat installed contribute to running hot? I plant to drain and replace water with coolant, but only after I get it running at a decent temp.

Water circulation seems much better.

230 isn't bad and yes, running just straight water at idle can be a problem. Water will boil at 212 degrees at sea level and atmospheric pressure. Every 500ft of elevation above that drops the boiling point of water by 1 degree. Allowing the system to pressurize to the standard 12-16PSI of most systems would raise the boiling point of pure water to 257 degrees F. Mixing 50-50 coolant/water will increase heat transfer and also raise the unpressurized boiling point to 223 degrees, which also brings the pressurized boiling point to 260+ degrees. The reason this matters is that when the coolant goes through it's phase change, it expands greatly and will push out the extra coolant from the system. It also creates little pockets of higher pressure and higher temperatures that will have significantly worse heat transfer properties. The steam will not absorb heat from the engine as well and it will not dump it out of the radiator as well either(if it makes it there).

This is why I will usually test run engines with no thermostat and the heater hose outlet dumping on the ground and the heater hose inlet connected to a garden hose running on full bore. This makes sure colder water is always cycling through the system and it won't overheat during break-in. Then I will run it a bit longer while letting the hose pull distilled water from a jug for about 2-3 gallons to purge the tap water out. Then I shut it off and let it all cool, check torques, etc... Then I will put a thermostat back in, connect the whole system and make sure I have it all topped off and a radiator cap on it before firing it up and letting it run normally to make sure it will come up to temp and thermostat will open and not overheat while also not leaking. Once all that is done, I drain the system again and then fill back up with 50-50 coolant-distilled water and I'm done.

 

[Bextreme04]

Rust also has a good point. Now is the time to check idle mixture and timing. If you are too rich or too lean it will overheat. If you have too much or too little base timing it can also overheat.

 

[KDizzle]

Verify that the timing isnt retarded. Anywhere around 10 initial or so would be a good starting point.

Timing is retarted at -4.

 

[Sad Sack]

This does help, I used it in a 75 Vette that tended run hot and it reduced my temps about 15 degrees:

Pardon Our Interruption

 

[Bextreme04]

Timing is retarted at -4.

4 degrees ATDC is wild. That will not help at all in most cases. Try moving timing to 4-10 degrees BTDC and it might help a lot.

 

[KDizzle]

4 degrees ATDC is wild. That will not help at all in most cases. Try moving timing to 4-10 degrees BTDC and it might help a lot.

Yeah, wasn’t expecting that. Adjusted to 10 BTDC and it sounds much better. Temp still climbed to about 215 (guessing on stock gauge) but even slower. I’m gonna get a temp gun to verify.

Appreciate you and Rust on the timing education. Didn’t realize how much that factors in overheating. I guess I was hoping to address overheating then timing. Lesson learned.

 

[Bextreme04]

Yeah, wasn’t expecting that. Adjusted to 10 BTDC and it sounds much better. Temp still climbed to about 215 (guessing on stock gauge) but even slower. I’m gonna get a temp gun to verify.

Appreciate you and Rust on the timing education. Didn’t realize how much that factors in overheating. I guess I was hoping to address overheating then timing. Lesson learned.

Now that initial cam break in is done, go through and adjust idle speed and idle mixture. That might help a lot as well.

 

[KDizzle]

This does help, I used it in a 75 Vette that tended run hot and it reduced my temps about 15 degrees:

Pardon Our Interruption

Thank you for the suggestion. I’ll give it a go once I get my coolant system locked in the next day or so.

 

[KDizzle]

Now that initial cam break in is done, go through and adjust idle speed and idle mixture. That might help a lot as well.

Will do. I’ll do some research and give it a shot. I did lower idle…just haven’t messed with mixture. Nervous about messing with carb.

 

[Bextreme04]

Will do. I’ll do some research and give it a shot. I did lower idle…just haven’t messed with mixture. Nervous about messing with carb.

What carb is it? If it is the original quadrajet it is pretty simple. You would just get it nice and warm, then disconnect the vaccum advance to the distributor and plug the port on the carb side. Then, with the engine shut off, screw both idle mixture screws clockwise until they gently bottom out, then unscrew them each 1 and 1/2 turns. Start the engine and then make sure your idle RPM is 700-750 rpm. Unscrew one of the idle mixture screws 1/4 turn at a time and let the engine rpm settle between turns. The idle will usually climb as you are adjusting. I will usually let it get to ~800-850RPM before I will adjust the idle back down to 700-750. You keep unscrewing the mixture screw 1/4 turn at a time until the RPM start dropping when you turn it out. Once you get a drop, you screw it back in until you find the setting that gets you the peak RPM. Once you find peak, adjust the idle to 750 RPM and then turn the mixture screw in until the RPM drops to 700 RPM(this will give you a slightly lean idle mixture, which is what the book calls for and will give you a nice quick startup and clean idle). Now you can do the identical adjustment procedure for the other side or you can do the procedure initially by adjusting both screws 1/4 at a time from the beginning(I don't like doing it that way with a dual plane manifold, because you generally will have slightly different mixture demands side to side).

 

[KDizzle]

What carb is it? If it is the original quadrajet it is pretty simple. You would just get it nice and warm, then disconnect the vaccum advance to the distributor and plug the port on the carb side. Then, with the engine shut off, screw both idle mixture screws clockwise until they gently bottom out, then unscrew them each 1 and 1/2 turns. Start the engine and then make sure your idle RPM is 700-750 rpm. Unscrew one of the idle mixture screws 1/4 turn at a time and let the engine rpm settle between turns. The idle will usually climb as you are adjusting. I will usually let it get to ~800-850RPM before I will adjust the idle back down to 700-750. You keep unscrewing the mixture screw 1/4 turn at a time until the RPM start dropping when you turn it out. Once you get a drop, you screw it back in until you find the setting that gets you the peak RPM. Once you find peak, adjust the idle to 750 RPM and then turn the mixture screw in until the RPM drops to 700 RPM(this will give you a slightly lean idle mixture, which is what the book calls for and will give you a nice quick startup and clean idle). Now you can do the identical adjustment procedure for the other side or you can do the procedure initially by adjusting both screws 1/4 at a time from the beginning(I don't like doing it that way with a dual plane manifold, because you generally will have slightly different mixture demands side to side).

What carb is it?

Wow, lot of great information.

I’ve got a Edelbrock 1406 Performer Series. Similar instructions?

 

[Bextreme04]

Wow, lot of great information.

I’ve got a Edelbrock 1406 Performer Series. Similar instructions?

Yes, same instructions. The problem with the edelbrock will be that a factory fuel pump is likely too much fuel pressure for it, so it will be pushing fuel past the needle and seat. They are also often set with way too rich of a jet from the factory. You would need a wideband to know just how much it is off and then use the needle/jet table to figure out what your correct ones need to be.