Engine Overheating

[sampsmit000]

I have a freshly rebuilt 350 in my truck. I run it for about 2-3 minutes and it starts to overheat. I have checked to see if the radiator is flowing and it is. I have replaced the thermostat and it still overheats. Where should I go/check next?

[cg285]

first question: what is it that makes you think it is overheating?

[Johnny Too Bad]

What is your current fan setup? Stock clutch fan, flex fan, electric fan? Do you have a good shroud? Have you checked your water pump?

[sampsmit000]

Originally Posted by Johnny Too Bad

What is your current fan setup? Stock clutch fan, flex fan, electric fan? Do you have a good shroud? Have you checked your water pump?

I am running a electric fan. No shroud but fan is about three inches from water pump pulley and I have checked that the water pump is running the right way and I made sure it was seated correctly. It's is brand new.

[sampsmit000]

The gauge says it is and everything inside the engine bay is very hot, like you cant even touch it.

[The Rocknrod]

Originally Posted by sampsmit000

The gauge says it is and everything inside the engine bay is very hot, like you cant even touch it.

Where did you acquire the temperature sending unit?

[sampsmit000]

Originally Posted by The Rocknrod

Where did you acquire the temperature sending unit?

I am not sure. The place that wired my truck installed it.

[ACK]

Just spit balling here, but some possibilities depending on the motor's set up ...
- Radiator hose is collapsing, needs an internal spring
- Timing is too advanced
- Fan is incorrect size, installation, or needs to blow in opposite direction

If you think it's any of the above, do a forum search for more info, they're all common culprits that come up from time to time. Good luck and let us know the outcome.

[Johnny Too Bad]

Originally Posted by ACK

Just spit balling here, but some possibilities depending on the motor's set up ...
- Radiator hose is collapsing, needs an internal spring
- Timing is too advanced
- Fan is incorrect size, installation, or needs to blow in opposite direction

If you think it's any of the above, do a forum search for more info, they're all common culprits that come up from time to time. Good luck and let us know the outcome.

All possible culprits. The first thing I would check is to make sure the fan is turning/blowing the right direction.

[sampsmit000]

I just bought a infrared gun. After idling for about 5-10 mins it was at 220 and then I drove it around the block and it was 250. I checked and the fan is blowing the correct way.

[Johnny Too Bad]

I would pull the thermostat and run it without one to see if it makes a difference. You can test the thermostat in a pot of boiling water to see if it's opening properly.
If it's not the thermostat, it could be your water pump is not operating properly. It may have a bad impeller that could be circulating the coolant, but not enough to cool the engine.
You said the coolant is flowing, but you might have enough of a blockage somewhere in the system to keep it from circulating enough coolant. Could need a radiator flush.

[shp4man]

Originally Posted by sampsmit000

I just bought a infrared gun. After idling for about 5-10 mins it was at 220 and then I drove it around the block and it was 250. I checked and the fan is blowing the correct way.

Where did you shoot it with the infrared? What's the radiator temp in the area where the top hose goes in?

[sampsmit000]

Originally Posted by shp4man

Where did you shoot it with the infrared? What's the radiator temp in the area where the top hose goes in?

I shot the intake manifold and the block. The top hose was 200

[WOLFMANmike]

Originally Posted by sampsmit000

I shot the intake manifold and the block. The top hose was 200

here are my questions for you as i have been through this last year and was beating my skull trying to figure it all out # ! what make of radiator are you running ? is it by any chance a Champion 3 row ? # 2 when you rebuilt the engine did you buy a brand new Distributor ? or did you use the old 1 ? # 3 as some one on here mentioned are you running a bottom hose with a spring in it ? now i will explain why i asked those... 1 about the radiator i bought a champion radiator i bought the 3 row thinking that it would be a better radiator more rows = more cooling right ? well turns out with them that is wrong by getting a 3 row they dont make the radiator bigger to accommodate for the 3 rows so the just make the 3 rows smaller .. yeah big problem so i called them up and complained and they sent me out a new 2 row radiator .. i did not install it yet tho at the time the 2 crow just so you know has two 1'' cooling rows much better radiator ok next .. was the bottom hose so i looked its kinda hard to see at idle speeds but yes also if i grabbed the throttle and reved it up to a cruising speed is started collapsing the hose .. and that was fixed by running a hose with a spring in it so for for check that as well ... next the distributor and timing ok so by now i have installed the new hose and put in a new 2 row radiator and its drive able now but yet as driving it up hills she get hot again ! then after the top of the hill is reached it cools back down WTH ? so i check and re check the timing its like in the happy spot of 14 deg should be fine well i finely pulled the distributor cap and turned the rotor to look at the advance weights and such ... boom found it ! the dist was not snapping back after i let go of it so while driving it it was staying at full advance lucky for me i had another HEI sitting here i bought new springs and weights for checked to make sure it snapped back and installed it ... now i get no hotter than 195 on a very hot day with a 185 Tstat .. so mine was the combo of all things i asked you today .... also these trucks really need a fan shroud they dont have much of a opening for cool air to get in so the shroud is a big deal ... hope all of this gives you a fix and your back on the road soon .... Happy truckin

[shp4man]

To see if the radiator is clogged, what's the temperature on the metal part behind where the bottom hose comes out.
My truck has a 195 tstat, top hose temp at metal about 198-200, bottom hose area at about 110-125.
On my truck, the 195 tstat helped cooling, plus my sender was inaccurate. But it's a six. Shouldn't make any difference.

[scuderia]

2-3 minutes from cold? Shouldn't even be warmed up by then... No overheating problems before the rebuild? Radiator shouldn't have gone "bad" sitting around. Hate to say it but if you didn't have the problem before then I'd look first at the rebuild . timing, head gasket waterpump. btw have you had the radiator cap of while starting from cold and watched what happens? Should see when the thermostat opens and coolant starts to flow. Shouldn't pump water out either when cold. Hope it's something easy.

[luvbowties]

One more thought: did you install a serpentine belt system during the rebuild/install? If so, did you get proper water pump that should now have a reverse flow (it turns backwards to original pump)?
Sam

[sampsmit000]

Thanks for all of the replies. Took it in. The radiator was blocked. Replaced it with an aluminum radiator. Now doesn't get any hotter than 205 even after driving for 45 mins in 100 degree weather!