I have used that steam port configuration without issue on several builds. It sounds like insufficient fan air flow. What fans and shroud are you running? Have you blocked off gaps around the radiator? Do your fans go to high speed when idling?

Don

 

I am using the shrouds that came withe fans.

Superior radiator - Camaro

I used the dual spal fans.

Have not blocked off any gaps.The fans to go to high while idling.

 

On my Gen 4 car, the cooling (steam) line from the heads runs in under the cap where you can see it. When refilling the system it can take a while to establish solid flow with no bubbles. Also it will not clear at idle speed, more rpms are needed.

 

I think I just found out one issue. Just ran the car to 205 and the thermostat did not open up. I am pretty sure the GMPP LS3 came with a 187 thermostat.

 

I had the same issue. When it warms up reach down and see if there is any flow in the lower radiator hose. If there isn't jack up the front end, open the radiator cap and squeeze that upper hose until your hands hurt. I believe I had a pocket of air trapped at the rear of the cylinder head which finally burped out allowing coolant to reach the thermostat and open it up.

 

Possible coolannt is not reaching T-stat due to air.

With the engine running squeeze the top hose, slowly pumping. Hose should feel firm. If not keep pumping slowly. This will draw the air out and hopefully get the stat to open.

Wear a glove. Lol

 

How firm should the hose be? I know that is subjective, but should you be able to collapse it all the way?

 

Shawn... You might want to look at an EMP/Stewart thermostat. With the three holes they have in the center section, its supposed to allow any air in the system to escape, plus if their thermostat gets stuck, it always allows some coolant flow.

"Manufactured by Robert Shaw and modified by Stewart, these custom thermostats feature a balanced sleeve design and are constructed for high flow, high RPM applications. Strongly recommended for any performance application - must be used with Stewart Stage 2, 3 or 4 water pumps. Our Stage 2,3 and 4 Small Block Chevy water pumps do not have the factory bypass hole, therefore we put three 3/16” hole in our modified high flow thermostats, this moves the bypass to thermostat. This also allows air to escape on initial system fill making bleeding the cooling system much easier."

 

Thanks Mike. It looks like you have to use their water pump as well.

 

Well both hands are tired and the thermostat still did not open. I filled the no spill funnel about an inch past the neck and the coolant only expanded. The bottom hose eventually got hot but again no drop in coolant. The car never got above 205. My low fan kicked off and on.

Picture is after coolant expansion.

 

Could you feel if there was coolant in the lower hose? It will feel sort of squishy/solid if that makes any sense - if empty it will be easy to squeeze closed. When I had this issue the hose would get hot but just from heat transfer not from coolant flowing through it.

 

Shawn, it looks like your upper radiator hose is lower than the back of the block. I don't see how you will get the air out if it is in the back of the engine. I have a radiator pressure fill kit. I also have the Lisle coolant "Burb" kit, but this kit uses pressure to force out the air and replace it with coolant. It works amazingly! If your upper hose is lower I don't see any other way to get that air out. Mastercool Vacuum purge and refill kit .

I wonder if you run it without a thermostat (simulating and open thermostat), it will have a better chance of getting the air out from the back of the engine and up to the radiator. Then, you can add the T/S.

Brett.....

 

Shawn, it looks like your upper radiator hose is lower than the back of the block. I don't see how you will get the air out if it is in the back of the engine. I have a radiator pressure fill kit. I also have the Lisle coolant "Burb" kit, but this kit uses pressure to force out the air and replace it with coolant. It works amazingly! If your upper hose is lower I don't see any other way to get that air out. Mastercool Vacuum purge and refill kit .
Brett.....

Thanks Brett. The picture is a little deceiving. The hose is higher than the back of the block, maybe not the very top of the rear of the heads.
I was thinking about one of those vacuum purge tools, but at this point I am not sure if an air pocket is actually my problem. I guess I could use one if I replace my thermostat.

after cool down.

 

Well yes, those kits are pretty expensive so I would not recommend getting one if you aren't sure that is what it is. Now, if you want to try one without spending the $$, I will send you mine and you can try it. If you decide you want to try one let me know and I'll send it your way.
Brett....

 

Thanks Brett. That is a very generous offer. If I decide I need one I will pick one up. It will help build my tool collection. Plus, it will still be cheaper than paying someone to fix it.

Another example of a great bunch of guys and girls on this site. 👍

 

Thermostats should have priming hole(s). If not, drill some.
Lower hose should have a spring/coil inside preventing from collapse when stat opens.
Top hose should be taut and hot when stat opens and system pressurized with good cap and tight system, meaning no leakage.

 

Are you squeezing with radiator cap on or off?

do you have a temp gun. maybe gauge issue?

 

I am squeezing with the cap off. I don’t have a temp gun, but the scanner and the temp gauge are spot on with each other.

 

I do it with cap off and the funnel installed in the cap half full of antifreeze. So it’s a closed system of sorts but air can escape through the funnel….

Make sure you raise the front of the car a foot or so.

Don

 

That is how I did it with the no spill funnel. I think I might just have to replace the thermostat. I don’t know what else to do.

 

The car has never overheated and I have never had any coolant come out of the overflow. I think the highest temp I have seen has been 223. So hopefully it is nothing serious.

 

With the cap off the system is not pressurized so the lower hose won’t get firm imho.

Hard to imagine you have a blown head gasket.

Don

 

You don’t know my luck,lol.

 

I would close the gaps around the radiator and see how it goes.

Only other thing I would check is make sure your fans are getting full voltage at idle. If the voltage is falling the air flow will drop.

Don

 

I would close the gaps around the radiator and see how it goes.

Only other thing I would check is make sure your fans are getting full voltage at idle. If the voltage is falling the air flow will drop.

Don

Thanks Don. I will check the voltage and see how I can close any gaps. As I mentioned the low temp fan turns on and off.

 

Shawn, I've got this on file for filing the cooling system on LS engines from Youtube. Although I can't say it works for sure it might help when filing with coolant.

Simon

 

Perfect, thanks Simon.

 

I actually think you are OK. When mine had air my temp gauge went crazy, like shot up to 275 in just a couple of minutes. Once I got the air out everything settled down and my temps run about 210 to 220 which apparently is correct for an LS - hotter than I was anticipating but I didn't really know.

 

Yeah, I even read that GM programmed the low speed fans to come on at some where around 230 degrees in some stock applications.

At some point I am going to change out my Dakota Digital fan controller for the PCM of NC controller. The DD controller works, but I have it wired to pull all the data from the their BIM module so I lose the fans when I connect to the DLC. This is makes it real pain to obtain live data. And what Don is saying about having both fans come on at low speed makes sense.

 

I recently spent a lot of timing chasing hot running temps with my car. You already jacked the car up and used a tall funnel, and left it like that overnight. You already have dual fans.

I'll add a few things to consider. Some folks will drill some holes in the stat to let air through, I know it was already mentioned. You might also want to look into your tune, one thing that helped my car which is pretty radical for street driving was adding more timing at cruise and at idle.

My car is LS 5.3, cammed, single 85mm turbo, air to air that blocks most of my radiator, single Taurus fan, 20.7 wide radiator core, and light traffic on Sunday when it was 90F out I ran in the upper 180s for a long time, hit bad traffic and got up to 204 but it cooled down to 193 when I was able to cruise at 50 mph for a few miles. My fan is programmed to come on at 185 and off at 180.

 

Before I had my buddy fix it (built a shroud, re tuned it), I idled 214-219, and got up to 230 on occasion.

 

The only easy way I was about to get air out of my system was to fill the antifreeze through the upper radiator hose slowly. I also have a couple holes drilled in my thermostat.

I also have the same radiator and fans. Mine will get up to about 212 or so when coming off the highway with the air on on a hot day while idling at a stop light. When I start driving it cools down very fast. It almost seems like the water pump isnt pumping enough water at low speeds.

 

I drained the radiator, tested the thermostat and it was working properly. Refilled the coolant using a vacuum kit and then burped it with a no spill funnel. Just took the car out and I am happy to report the car only got to 210 once. In fact it stayed below 200 for most of the drive. It was only 84 so the real test will be the high 90’s.

Everything is not ok with my Dakota Digital controller. For some reason the fans will not run after I turn the key off. It worked when I first installed it. All the fuses are good.