5.3 swap coolant problems

[mopar250]

Hey guys,
I have swapped a 5.3 into my 80 short bed and ran into a problem now that I have it running. Now that i've filled the cooling system, the engine won't take any coolant. When I start up and let it run for a while the temps on my guages get up around the 220 range and both radiator hoses are still cold. My gauge package is new but since the computer kicks the fans on at 180 or so I believe it that the engine is at 200 plus. I have a non stock radiator but i've only added about 2 gallon of antifreeze and looking around at capacities I need to be at 3.xxx. I assume its one of a couple things, either and air bubble or I possibly put the thermostat upside down? I started this whole crusade over a year ago so I don't really remember much about the thermostat other than I put a new one in. When warm I can turn the rad. cap and there is pressure in the system. Anyone have any good ideas to try?
Thanks!

[TwinsSpeedShop]

Originally Posted by mopar250

Hey guys,
I have swapped a 5.3 into my 80 short bed and ran into a problem now that I have it running. Now that i've filled the cooling system, the engine won't take any coolant. When I start up and let it run for a while the temps on my guages get up around the 220 range and both radiator hoses are still cold. My gauge package is new but since the computer kicks the fans on at 180 or so I believe it that the engine is at 200 plus. I have a non stock radiator but i've only added about 2 gallon of antifreeze and looking around at capacities I need to be at 3.xxx. I assume its one of a couple things, either and air bubble or I possibly put the thermostat upside down? I started this whole crusade over a year ago so I don't really remember much about the thermostat other than I put a new one in. When warm I can turn the rad. cap and there is pressure in the system. Anyone have any good ideas to try?
Thanks!

LS motors don't flow like old school motors and this means that you can't fill the radiator and let the motor take it in as it runs. I learned the hard way. You have to fill the block as well as the radiator to get it to flow and cool.. Have you done this?

[kevmac]

^^^. Did they same with my camaro. Pull the upper rad hose and pour it in

[mopar250]

Thanks for the tip guys I'm going to go give that a try. I am sure that's what it is because it for sure won't take any in now. Go figure I figured out the miles of wiring and thousand small details and just pouring in coolant gives me issues....

[truckdude239]

Yea i put 4 and half gallons in my 71 with 4.8

[mopar250]

Ok I gave it a try adding coolant to the engine threw the radiator hose. I took the top hose off from the radiator and as soon as I added anything it just came right out of the radiator. Do I need to drain the system and try all over again? It seams strange that I add to the top of the engine and it flows out of the radiator? Almost like the engine is full? I tried both with the engine cold and running.
Thanks!

[BR3W CITY]

Are you sure the thermostats just not stuck?

[Angryman117]

Sounds like a stuck thermostat to me. I filled mine just putting coolant in the radiator like normal and no problems here. Feel your heater lines they should heat up quick, see if your heater is putting out hot air. The upper and lower raidator hoses won't heat up until the thermostat opens.

[mopar250]

I will look into the thermostat next. I put a new one on before the engine went in but I guess that doesn't mean it's working properly. The upper and lower hoses are defiantly not warm but didnt check the heater hoses.

[Houston Ben]

I did the same as you Mopar. At first it wouldn't take, then once the engine was hit I started squeezing the lower hose and must have heated the thermo as it all of a sudden took the water. Been good since.

[mopar250]

Little update, I got a new thermostat and replaced the coolant by having the truck up on jackstands in the front and poured the coolant in threw the top radiator hose. I think I've added much more coolant this time so i I'm very sure its in the motor this time. Will know tomorrow morning if I have success. Little to late to wake everyone up here at home.

[chuckmc8]

For general info, In LS based motors, the thermostat is the one of the lowest points in the cooling system ( rather than high like reg SBC) and the thermostat will block coolant from flowing into the the engine if you fill just through the radiator cap in a swap situation. . In the factory configuration (donor vehicle) the coolant system fills through plastic tank into the "wye" in the front heater hose (on the engine side of the thermostat) and fills the engine block first, then the radiator. If you don't have that wye, you have to manually fill both sides of the thermostat to get coolant into both radiator and engine block. In swaps, if you fill the radiator full and not the upper rad hose, youll think all is 'cool' till you start the engine and it will get HOT in a hurry!

[mopar250]

Success! I was able to fire the truck up this morning and within a few minuets had it up to 190 or so and it stayed right there. I could feel warm water in the upper and lower hoses. Chuck is right, the system is opposite of the normal SBC cooling system and when you think about it that way it makes perfect sense that the engine would need to be filled up first to allow the coolant to be drawn through.
Thanks for the help guys!

[BR3W CITY]

Awesome. fwiw, you can take a small torch and lightly heat the stat to get it to open with the truck off. You need to be careful to apply just enough heat, but in a pinch its nice to be able to manipulate.

[Matt Cramer]

Originally Posted by chuckmc8

For general info, In LS based motors, the thermostat is the one of the lowest points in the cooling system ( rather than high like reg SBC) and the thermostat will block coolant from flowing into the the engine if you fill just through the radiator cap in a swap situation. . In the factory configuration (donor vehicle) the coolant system fills through plastic tank into the "wye" in the front heater hose (on the engine side of the thermostat) and fills the engine block first, then the radiator. If you don't have that wye, you have to manually fill both sides of the thermostat to get coolant into both radiator and engine block. In swaps, if you fill the radiator full and not the upper rad hose, youll think all is 'cool' till you start the engine and it will get HOT in a hurry!

As my truck has a heater hose fitting on the radiator (currently capped off) - would it make sense to add a wye between it and the front heater hose?

[BR3W CITY]

IMO not really, unless that also ended up being a good place to put your steam-burp. (aka the high point on the steam line system). Once the system is full and pressurized, the Y doesn't serve much of a purpose, unless you drain your block regularly.

[79 big block]

I'm glad I found this thread, I just tried to fill the radiator through the cap and had the same problem of no coolant in the motor. I'm about to go try this again.