LS swap radiator size / overheating issues

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Funco4JM

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This summer I decided to swap my Turbo Honda for an LS1. The engine came out of a running sand car before it was pulled out. I have two thoughts and I am looking for direction before I start to replace a bunch of stuff. After filling the radiator and expansion tank, I fired up the engine and let it warm up. The needle on the gauge hovers just under 210* at idle sitting in the garage with an ambient temp of 100*-105*. If I let it sit for 15-20 minutes, the gauge temp will slowly start to increase, and the engine will get hot (it goes to the line between 210 and 250) and then I shut it down. If I take it out on the road, the engine starts to get hot even while cruising at 2000 rpm in 4th gear, same issue. Don't want to overheat it so I shut it down. (I did fill the radiator all the way and forced coolant into the expansion tank to be sure / I also burped the heads numerous times to be sure it wasn't a steam issue).

1 - My radiator in the car is a CBR 31x19 with dual 14" fans. It is about 16 years old as it seems to be original to the car. With the swap, I had the inlet/outlet fittings moved from one side of the radiator to the other side of the radiator. Two questions... First, does moving the inlet/outlet from one side to the other pose any cooling problems with the radiator? Second, do radiators go bad?! The fans work fine and come on one at a time at preset temps from the computer. 

2 - My cooling lines are hard lined 1.5" and 1.25". Is it possible with them being near the headers that they are heat soaking that fast? 

With as late in the summer as we are and only a month to get this figured out, my options are to replace the radiator completely, replace the cooling lines with -20AN soft lines, or replace both. If I do both its going to be another 2K. 

Help!!!!

 
Before you get too far check to see if you have a thermostat in the system. I remember way back removing the thermo and installing a solid restrictor (drilled out plug) to regulate flow. No idea if it’ll help but $2 may be a better initial step than a redo?

 
FWIW......... My LS has plugs on the clutch side of the motor & this on the WP side of the motor and no Thermostat.  I found this crossover plugged up & it caused it to get hot & would not bleed out @ all.  I could tell it was boogered up because there was no water flowing in the radiator as I looked down into it.  I removed this & soaked it in CLR & then dug all of the crap out of it with a small screw driver.  put it back together, filled it up & as soon as I fired it up, I got coolant flow & it was completely happy again. 

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I swapped honda to a LS in my last car. Same size radiator as yours. Just make sure its a dual pass and your fan shroud is air tight around the perimeter. As mentioned above about no thermostat, thats how mine was set up.  I moved the inlets on radiator and went to hard line 1-1/2 with silicon elbows on both sides. Cant do much about the heat soak. What model are your fans? CFM might be a issue.

 
If your radiator is a dual pass then changing the inlet and outlet are your problem. The dual pass needs to have a wall (horizontal) in the radiator tank between the upper and lower hoses. Without that the water dumps in the top and goes straight out the bottom of the same tank without being forced through the radiator.

Post pics of the radiator

 
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I’d make sure water is flowing through your radiator before you get too far. 

 
Mike E and Jtmney714 are the winners! 

Called CBR just to check on the movement of the inlet/outlet... basically it turns it into a coolant tank. The fluid doesn't flow through properly which is why once it heat soaks its done. 

I ordered a new radiator today with 16" fans and the inlet/outlet on the correct side. Should solve the problem!  Thanks for all the responses. I'll let y'all know once I get it and install it. 

 
One other thing we've learned the hard way (unlikely the case here) fixing a thrown belt in the dunes: it's super easy to route the belt wrong and reverse the water pump rotation.  It won't pump chit spinning backwards.  

 
I second "Rockwood's" post. Also have seen where someone did a motor swap an connected inlet an outlet piping wrong (backwards) to the radiator.

"HJ"      :ex:       :cheers:  

 
LS are also really bad about getting air trapped in the system and will for sure run hot. I jack my car up to create a high side in the front (rear of engine) and remove the steam ports till solid water flow comes out. 

 
Mine has a low-mounted radiator and they had it set up with the pressure cap on the top of the radiator, i.e. lower than the top of the engine. It would not circulate the water at all. I cut of the radiator cap neck and had a 1/2" NPT bung welded on in place of it, and added a high-mounted aluminum header tank with the pressure cap on top and a line going to the top of the radiator. Also added a small "steam" line going from the top of the engine that spills into the top of the header tank, so it is constantly venting any trapped air from the engine. That cured it.

 
One additional question...  What size radiator cap do you guys use?  15lb, 18lb or 21lb?

 
The LS motors run super cool, We build about 20 motor a year and install about 5-10 per year, 

Lets see the pics of the radiator to make see if it was fabbed correctly, 

the LS water pumps have a bypass valve that is part of the thermostat, this will keep your Plastic Radiator in your camaro from blowing apart, so if yo have a plastic radiator keep the bypass valve in it with a thermostat, 

If you do not have a Camaro with a plastic radiator, then you can remove the thermostat, but must plug the bypass hole or the water will just go round and round the water pump and water will never leave the pump, it will go from the back side of the pump then to the front side, 

WE BUILD MOTOR, NOT CHASSIS, this being said, get rid of the expansion tank and run a OVERFLOW TANK WITH RADIATOR CAP on the radiator, 

steam ports are to fix a design flaw of the motor, the water pump sits below the top of the head,  so it lets the air that can not make it to the pump out, the steam port needs to go to the outlet hose, or back to the RADIATOR on the outlet side, 

The Thermostat is on the bottom of these motors, so if yo run a thermostat, (i do) then drill around 6-8 holes in it, to let the water fill the motor, doing this will help fill the motor like any standard SBC,  Dont want to deal with a thermostat, or bypass plug, REDLINE make a thermostat delete plug, very nice part, 

After you figure out the water, a big part of overheating on a LS is oil temp,  dont know your oil temp, then keep the runs short, now the that oil temp stays around 220, the water never gets over 175, when the oil temps hit 320 the water was around 220,   keep everything cool,    

 
Mike E said:
If your radiator is a dual pass then changing the inlet and outlet are your problem. The dual pass needs to have a wall (horizontal) in the radiator tank between the upper and lower hoses. Without that the water dumps in the top and goes straight out the bottom of the same tank without being forced through the radiator.

Post pics of the radiator
Click to expand...


Funco4JM said:
Mike E and Jtmney714 are the winners! 

Called CBR just to check on the movement of the inlet/outlet... basically it turns it into a coolant tank. The fluid doesn't flow through properly which is why once it heat soaks its done. 

I ordered a new radiator today with 16" fans and the inlet/outlet on the correct side. Should solve the problem!  Thanks for all the responses. I'll let y'all know once I get it and install it. 
Click to expand...
I'm surprised the person modifying your radiator didn't realize what they were actually doing.

 
Kraut_n_Rice said:
I'm surprised the person modifying your radiator didn't realize what they were actually doing.
Click to expand...
I dont think he actually cared or thought about it to be honest. I called and asked if they could do it, dropped off the radiator and gave him detailed instructions on what to do... I would imagine it would be my fault for being so sure of what I wanted. The stupid part is if I had him cut off the mounts and rework them by flipping the radiator over, this wouldn't have been an issue. Now I have a radiator that I need to have fixed just to keep as a spare or sell for cheap. 

But through all this I ordered a new CBR with 16" fans and a fill cap... Its puurty...

Rad.jpg

 
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