LS Overheating Issue

Looking for any advice on keeping my swap cool. Just got things running and am running the following on a 6.0 Aluminum block l76:

- Texas Performance Concepts Turbo LS Style Radiator with dual fans
- New gm water pump and 160* thermostat
- TPC ac system with new condenser.

Ive made sure all air is bled and coolant is flowing through the thermostat. Both upper and lower radiator hoses are hot.

I can idle and the car will slowly creep up to 210 which takes about 25 minutes...when i go for a drive around the block the car gets up to 230 + then i shut it down, i am not running the ac.

I have both fans set to be running at all times.

Any thoughts or advice would be great! Thanks.

LS motors like to run in the 200 plus range. 230 is kinda high though. You are hitting 230 with fans on high speed? Are you running your fans through the GM ecm or stock porsche radiator sensor? You might be running lean if your temps are picking up while driving. Bad water pump is a possiblity as well. Temp should drop when you are cruising.

Hey Leva,

Thanks for the response. Fans are single-speed fans from TPC that look like generic 10" radiator fans. Using the GM ECM to run, set hp tuners to run the fans at all times. I have individual relay's setup to control each fan, but have only been running with both two on.

Based off of ltft and stft's i dont think im runing lean, but i do have a wideband sensor in just need to wire it up.

I think the water pump is pumping ok since temp drops a few degrees when I increase rpm when idling.

Seems like underload is the issue, ill check for lean conditions.

If your trims look in line then fueling is prob not an issue. From basic overheating diagnostics, normal temps during idle and overheat during cruise usually indicates a fan or water pump problem. Maybe have someone gas it while squeezing upper radiator hose. You should feel a strong pulse. Did you perhaps wire your fans backwards? Ha, been there, done that.

I didn't trust myself...so I did check the wiring. both fans suck a piece of paper against the radiator pulling air through the radiator.

I haven't tried letting the car idle long enough to reach the same temps as cruising. I will check that as well tomorrow alongside the water pump. The temps definitely seem like they want to creep above the normal 210* im used to with LS setups. Driving around town I may not have enough airflow, may have to look into other fan options.

what heater valve are you running? are you running the stock porsche "shut off" style valve, or a bypassing valve?

the design of the ls cooling system relies on coolant flowing through the heater at all times in order for the thermostat to work correctly. coolant flows out of the block into the water pump, goes down to the backside of the thermostat and out the heater hose to the heater. if coolant is not flowing the past the back of the thermostat the you end up with a cooler spot around it and it wont open till much hotter than the open temp. when the thermostat does open, being its on the inlet side the burst of lower temp coolant will cool the thermostat pretty quick and end up closing it. the top rad hose and rad will get hot and seem like coolant is flowing, despite the fact its not flowing properly.

ive fixed this problem on a number of ls swaps. if your valve is vacuum operated (late cars) i use a heater valve from a late 90s chevy truck. the other option would be to put an H valve in the system between the heater outlet and the heater valve.

Hey sharkey,

I have an h valve setup with a new manual heater valve (early 85 car).

I know I’ve got solid flow through the heater core, I’ll do some testing with the heater control valve wide open to make sure it’s not a restriction through the h valve.

Just an update, not a solution yet, for anyone with similar issues:

I removed the heater circuit from the engine, just have a single hose connecting the water pump heater outlet and return. This did not make any noticeable change.

AFR verified to 14.6+/- idle, mid 12's when wide open, and high 14's to low 15's when cruising.

What are people running for fan or fans setups?

I run an stock n/a radiator and fans with a 3 relay wiring setup. 215 is the highest i have seen my temp hit. And that is idling. Cruising it quickly drops to around 190.

I had a similar issue with my truck a few years back after swapping a leaking radiator. Turned out i got a bad replacement.  I could idle the truck all day. Would only overheat cruising or under load. Maybe something to consider since it seems you covered all your other bases.

How does the car run? The only other thing i can think of is a blown or mismatched head gasket or clogged exhaust.

Ha, or maybe your gauge is reading incorrectly.

I'll try and check everything before I go the radiator route. This was a new radiator from TPC so hopefully not the case but sounds like a similar situation to your truck.

The car runs well. All-new exhaust, utilizing a Lindsey 3" kit. I did check for a blown head gasket using a combustion leak detector and didn't see anything with that, not to say its not mismatched, it was a junkyard engine. It didn't look like the engine had been opened up previously when I changed the pan and valve covers.

I would suspect the gauge, except I am logging the gm gauge on the driver side head through hp tuners and using a VDO sender to the OEM gauge on the passenger side head, and both are reading the same.

Yes, the radiator would be a last resort. Maybe double check your fan function and settings. Are you using the gm ecm or the porsche relays? Are you certain high speed is switching?

Also, I remember a post from someone regarding an overheating issue that resulted from him forgetting to reinstall the plastic diverter that goes near the top of the radiator inside the nose of the car.

rjarvis wrote:I'll try and check everything before I go the radiator route. This was a new radiator from TPC so hopefully not the case but sounds like a similar situation to your truck.

The car runs well. All-new exhaust, utilizing a Lindsey 3" kit. I did check for a blown head gasket using a combustion leak detector and didn't see anything with that, not to say its not mismatched, it was a junkyard engine. It didn't look like the engine had been opened up previously when I changed the pan and valve covers.

I would suspect the gauge, except I am logging the gm gauge on the driver side head through hp tuners and using a VDO sender to the OEM gauge on the passenger side head, and both are reading the same.

I can tell you from past experience on multiple builds, that the fans from TPC won't keep it cool in any kind of hot weather. All of my builds that I do now, I use the TPC radiator and adapt the stock 944 fans to it. Never had an overheat since using the stock fans. You can cut out the center of the TPC fan shroud for the stock fans to bolt to.

Dallas - I am definitely going to upgrade the fans. Unfortunately, I don't have the original fan shroud/setup anymore. I found some high cfm 10" that I plan to install.

Leva - I will have to check on the diverter...I don't recall any piece in there currently. It does seem airflow related since overheating still occurs even when driving at 50 mph, at this point fans shouldn't be playing much of a role.

I am using the GM ecm and two relay's I added. I have it programmed to run the fans at all temps currently. The fans are single speed, so always running max.

There are stock fans on ebay. I have yet to find an aftermarket fan that will do the job. I have a customer now that has a 944 LS with the biggest electric that will fit on the radiator, and it overheats. I have ordered a stock fan from ebay for it.

Fans from a 99 V6 ford contour fit and flow a ton.... they work well, but it's a little work to get them to fit.

Imo, the stock dual fan setup is the way to go. My stock na setup original to the car with 120k has served me well. I would not bother trying to retrofit any aftermarket setups. I believe the perfect fitting stock shroud design is why they work so well. And of course this is just my opinion. To each, their own.

Thanks all for the advice - i will go back on the fans for sure.

I think I figured out the issue...unfortunately, I won't be able to test and update the thread for a couple of weeks as ill be out of town.

I ordered a new water pump when i got the engine (L76 from an 08 pontiac gt). Rock auto had a melling 503 water pump listed as the replacement...as does mellings website. When I dig into it deeper it seems to be that this is listed as a "standard" rotation water pump. Every other option I can find is reverse rotation. As with almost all LS setups I know the water pump rotates counter clockwise, opposite of the crank. From what I've seen this is indicated by a grooved water pump pulley for standard and flat pulley for reverse rotation.

If anyone experiences something similar, give that a check. Water temps at Idle were ok, but under load as the pump would not be flowing this would be the problem.

i have never seen an ls engine that runs a standard rotation water pump. that pump is listed as a stock replacement for a corvette/ctsv/g8, all of those cars use a reverse rotation pump. combined that with a smooth pulley, the "standard rotation" has to be a typo.

sharkey wrote:i have never seen an ls engine that runs a standard rotation water pump. that pump is listed as a stock replacement for a corvette/ctsv/g8, all of those cars use a reverse rotation pump. combined that with a smooth pulley, the "standard rotation" has to be a typo.

You are correct, I reached out to melling. Apparently their terminology is “standard refers to the same direction as oem” in this case oem is reverse so the pump is the correct direction.

Like Sharkey said, that has to be a typo. All LS water pumps are reverse rotation.

Do you have steam lines hooked up to circulate the steam out of the system in the heads? If you don’t use them you can have heat issues, and your number 7 will get really hot... I used trick flows steam vents and they helped a lot. I’m about to switch to Motion Raceworks because they are a little nicer though. If you want the trick flow setup let me know. I’ll sell it to you for half of what it cost me. As far as Rad and fan setups go, I used a C&R Racing Rad and I adapted a Derail dual fan shroud to it.

Had a similar issue with my build. Went with two of the largest Derale fans I could mount on a shroud and haven't had any issues since doing so.

zeusrotty wrote:Do you have steam lines hooked up to circulate the steam out of the system in the heads? If you don’t use them you can have heat issues, and your number 7 will get really hot... I used trick flows steam vents and they helped a lot. I’m about to switch to Motion Raceworks because they are a little nicer though. If you want the trick flow setup let me know. I’ll sell it to you for half of what it cost me. As far as Rad and fan setups go, I used a C&R Racing Rad and I adapted a Derail dual fan shroud to it.

I do have the factor steam lines hooked up. Its also how i make sure all the air was bled out when filling the engine with coolant.

I am going to try and use the TPC Turbo Radiator Kit i have but swap out his fans for dual perma-cool 10" fans. I'm not convinced that's my issue though, as i cant keep temps down even cruising on the highway.

rjarvis wrote:Looking for any advice on keeping my swap cool. Just got things running and am running the following on a 6.0 Aluminum block l76:

- Texas Performance Concepts Turbo LS Style Radiator with dual fans
- New gm water pump and 160* thermostat
- TPC ac system with new condenser.

Ive made sure all air is bled and coolant is flowing through the thermostat. Both upper and lower radiator hoses are hot.

I can idle and the car will slowly creep up to 210 which takes about 25 minutes...when i go for a drive around the block the car gets up to 230 + then i shut it down, i am not running the ac.

I have both fans set to be running at all times.

Any thoughts or advice would be great! Thanks.

I had simular issue and i fixed it with new Spal fans and a new 250 amp altenator.Weak altenator can affect your fan output. Not sure if i needed to or not but i also added a auxilary radiator along with the 3 row aluminum radiator and used a bleed funnel to get any trapped air out of systym and havnt had any more issues . I usally run temps around 195 to 205 on 80 degree days and 210 to 220 on 95 degree days . I also have extra venting to help get the hot air out of engine compartment .

stu wright wrote:

rjarvis wrote:Looking for any advice on keeping my swap cool. Just got things running and am running the following on a 6.0 Aluminum block l76:

- Texas Performance Concepts Turbo LS Style Radiator with dual fans
- New gm water pump and 160* thermostat
- TPC ac system with new condenser.

Ive made sure all air is bled and coolant is flowing through the thermostat. Both upper and lower radiator hoses are hot.

I can idle and the car will slowly creep up to 210 which takes about 25 minutes...when i go for a drive around the block the car gets up to 230 + then i shut it down, i am not running the ac.

I have both fans set to be running at all times.

Any thoughts or advice would be great! Thanks.

I had simular issue and i fixed it with new  Spal fans and a new 250 amp altenator.Weak altenator can affect your fan output.   Not sure if i needed to or not but  i also added a auxilary radiator along with the 3 row aluminum radiator  and used a bleed funnel to get any trapped air out of systym and havnt had any more issues . I usally run temps around 195 to 205  on 80 degree days and 210 to 220 on 95 degree days . I also have extra venting to help get the hot air out of engine compartment .

I have some new fans on the way hopefully that will help out. Im running a gm 140 amp alternator.

People have mentioned a plastic diverter that should be near the top of the radiator...anyone have a picture of what this should look like? Or any other plastic air diverters that should be in place?