Overheating Rebuilt 350

[KDizzle]

Hello. Got an 86 K5. Originally came with a 305/TBI, but a 350/carb was installed back in 97 when I purchased. 350 block came from a 69-79 vehicle, based on my research. Block and heads rebuilt by machine shop this past April. Motor removed and installed by me. First time…somewhat mechanically inclined. Part of rebuild consisted of serpentine belt conversion. Got some pulley brackets from a 90 S10 V6 in a pick n pull along with a reverse flow GM water pump from Rock Auto for a C3500 5.7 pickup. Just attempted “break in” for 20 mins. Only got to about 15 mins before water was steaming/spewing/boiling from overfill and rad cap. Engine sounded fine, it just completely went nuts on the temp. I’m pretty sure I installed tstat correctly, even drilled hole in it as instructed. Not sure about bypass. Considering it was a fresh rebuild, wouldn’t think there would be an issue there. Don’t need a temp gun to know it was hotter than the surface of the sun. Someone suggested belt routing may be the issue?? Sure hope I didn’t screw anything up with the “semi” break in.

 

[Ricko1966]

Are you sure you got a reverse rotation pump? Lot of work, but big risk here if you are trying to break in a flat tappet cam. I'd pull the pump back off and make sure it's right. I'd also take the thermostat out and replace it after break in.Also inspect the pump, just because it's new does not mean it was assembled correctly, impeller not pressed on all the way, wrong impeller etc. If you didnt have overheating problems before. The most obvious cooling system change you made was the serp belt and water pump. What heads are you using? Was there a fan on it? We're you also blowing air into the radiator with a box fan?

 

[KDizzle]

Stock fan attached. Some resistance when I spin it with engine off and cool. No box fan was used. Lower shroud only. Same number stamped on water pump associated with pump I purchased. Pics attached. As far as the heads, they’re stock GM (3973487: 68-79). They were rebuilt too. Nuthin fancy with valves. Not sure on those specs. Before I tackle removing water pump, could I remove thermostat completely and see what happens? Will that give me a better idea? Of course, this would be temporary and just a diagnosing measure only. I’ll lift the front end as well to allow any air pockets to escape.

 

[Ricko1966]

No thermostat. Running, look in the radiator, make sure water is circulating. Replace tstat after engine breakin. I hope you are keeping things up in the 2000 rpm range for the first 30 minutes. Blow air in from the front and put your shroud on

 

[Bennyt]

Stock fan attached. Some resistance when I spin it with engine off and cool. No box fan was used. Lower shroud only. Same number stamped on water pump associated with pump I purchased. Pics attached. As far as the heads, they’re stock GM (3973487: 68-79). They were rebuilt too. Nuthin fancy with valves. Not sure on those specs. Before I tackle removing water pump, could I remove thermostat completely and see what happens? Will that give me a better idea? Of course, this would be temporary and just a diagnosing measure only. I’ll lift the front end as well to allow any air pockets to escape.

Stock fan? New stock Reverse rotation fan or original rotation?

After looking at our serpentine trucks, looks like you might have the wrong fan.

Yours: Leading edge to drivers.

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Mine: leading edge to passenger side.

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[KDizzle]

After looking at our serpentine trucks, looks like you might have the wrong fan.

You’re correct, I have the stock standard rotation fan, which is wrong for serpentine setup. I need a reverse rotation fan. Good looking out and Thank you!

How did you find yours? It looks stock.

 

[KDizzle]

No thermostat. Running, look in the radiator, make sure water is circulating. Replace tstat after engine breakin. I hope you are keeping things up in the 2000 rpm range for the first 30 minutes. Blow air in from the front and put your shroud on

As Bennyt pointed out, I have the wrong fan. I’m guessing address that first and try again? Would it still be a good idea to remove thermostat and let it flow for the remaining breakin cycle if all is well with water pump?

Yes, RPMs in the 2000s but only for about a combined 15 mins.

Thanks again for your replies!

 

[Bennyt]

You’re correct, I have the stock standard rotation fan, which is wrong for serpentine setup. I need a reverse rotation fan. Good looking out and Thank you!

How did you find yours? It looks stock.

Dont forget to buy the correct fan clutch.

I just noticed i dont have the idler brace to intake that you have. Im going to have to look to see if i forgot to put it on or if mine just didn't have it now.

I bought the complete serpentine system with all hardware, etc for $80 off an 89-91 Suburban that was being parted out. Spent another $200 - 300 on belts, powdercoat, ac delete, rebuilt alt, rebuilt ps pump, idlers, etc. I wanted something super reliable and easy to fix and get parts for anywhere.

Wish i could find a similar system for my BB in my C30. It has serpentine and v-belt combo. Works but i dont like it.

 

[KDizzle]

Good point on fan clutch.

Yes, I really like this GM serpentine setup. Very clean and relatively inexpensive…compared to aftermarket. Got the same setup in my Jeep YJ SBC. That and a little research led me to doing this to my K5. The YJ was definitely a good reference point. Just tried to mimic it. Only thing, it has an electric fan, so no visual on the mechanical fan.

Good luck on BB! Maybe a project for me if and when I decide to replace current SB in K5.

I’ll keep yall posted on overheating and new parts. Thanks again!

 

[Ricko1966]

As Bennyt pointed out, I have the wrong fan. I’m guessing address that first and try again? Would it still be a good idea to remove thermostat and let it flow for the remaining breakin cycle if all is well with water pump?

Yes, RPMs in the 2000s but only for about a combined 15 mins.

Thanks again for your replies!

I'd finish breaking it in, no thermostat. That was a good observation on @Bennyt s part.

 

[HotRodPC]

Even with the wrong fan though, you're just talking a stationary break in? How hot is it where you're at? I'm kinda thinking even with the correct rotation fan, it's not going to make much of a difference. So long as the water pump is circulating coolant, it shouldn't get that hot that fast. I've started engines up sitting on frame stand on the ground with no fan at all and let them run and they never got hot. I'm only talking 20 to 30 minutes or so, but no strain, WATER at the time in the radiator heater hoses blocked off, no fan. It didn't overheat. I was going to go right for the wrong rotation on the water pump, but it sounds like you've addressed that already. Hopefully I'm wrong and it's that fan.

 

[Sad Sack]

Silly question, but has to be asked, you didn't put the thermostat in upside down by any chance? Cone pointed up right?
Just guessing here but if radiator flow is good which would indicate a working WP, proper rad cap, proper fan, has correct head and manifold gaskets and tstat are all good almost sounds like trapped air.

Side note:
Can always boil the tstat in a pan as a test and watch functionality.

 

[Bextreme04]

When I have broken them in on a stand.... no fan, no thermostat, radiator hooked up, output from intake to heater dumping on ground, inlet from heater to water pump connected to garden hose turned on all the way. I usually put a big box fan I have in my shop right in front of the radiator as well.

Everything is so tight and breaking in at 2200 RPM... it WILL overheat if you aren't careful.

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.

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I would actually probably just order the set that they have listed that includes both the water pump and clutch, then order the fan they have listed for the same vehicle. The fan is a Dorman 621-108 and they don't say if it is standard or reverse... but summit sells it and lists counterclockwise rotation(which is reverse and what you want). https://www.summitracing.com/parts/...UGECu95SiwOu4fjKtH_sSV0DSoSEZj73TzhO5ctSpR6Hq

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[KDizzle]

Even with the wrong fan though, you're just talking a stationary break in? How hot is it where you're at?

Yep, stationary break in. Middle GA. Gets hot, but not enough I’d think would factor in to my overheating issue. It’s in shop, with some air circulation. I’m leaning towards water/coolant circulation issue. Correct fan and fan clutch are a must.

 

[KDizzle]

Silly question, but has to be asked, you didn't put the thermostat in upside down by any chance? Cone pointed up right?
Just guessing here but if radiator flow is good which would indicate a working WP, proper rad cap, proper fan, has correct head and manifold gaskets and tstat are all good almost sounds like trapped air.

Side note:
Can always boil the tstat in a pan as a test and watch functionality.

I’m pretty sure thermostat was installed properly. Just removed. Pic attached.