Thermal issues, aka over heating question

[rkleypas]

I'm sure it's something real simple, and hopefully someone here can help. I've been having over heating issues since the Power Tour. LS7, twin e-fan Be Cool radiator. Gauge is showing 250 degrees after idling five minutes. Fans are running and temp keeps climbing. The funny part is the lower hose and lower part of the radiator aren't hot at all. There are some black flecks in the anti-freeze. Bad water pump? Thermostat? Air bubble? The cam was swapped to a milder one before the tour.

[dontlifttoshift]

Sounds like a gauge problem.

[Che70velle]

Cold spots on radiator body usually indicate an area where coolant isn't flowing through, as in a blockage. Are hoses building pressure? What water pump are you running?

[MarkM66]

Have you opened the system recently? A quick heat up at the sensor can sometimes come from an air pocket.

[rkleypas]

Are hoses building pressure? What water pump are you running? I can squeeze the hoses when it's running. The upper one is hot, the lower hose is room temp after 5 minutes of idling. Not sure if I should be able to or not? The pump is the Wegner accessory drive water pump. Less than 3,000 miles on it.

Have you opened the system recently? Yes, the cam was swapped out before the Power Tour. Never had an issue before that.

Could the thermostat be sticking or bad? Never looked at an LS thermostat, but there are flecks of black rubber in the radiator.

[Vince@Meanstreets]

You might have a gauge or sending unit issue. Never seen a LS get to 250 that fast idling. One hose should be hot @250.

Borrow a thermometer and verify temperature.

Then get the air out of the system.

[rkleypas]

Is the best way to get air out of the system to jack up the front of the car and run it with out the radiator cap? Should I do this a couple of times over a few days? I don't mind buying a tool if that's what I need...

[GregWeld]

Do you have an overflow with a return? Do you have steam vent return plumbed?

The thermostat most likely isn't the issue. Steam pockets are more likely. Had this issue on my LS3 480HP --- and I spent 3 days tearing into it.... the culprit was no overflow tank and every time it warmed up - and cooled down - it sucked in air which eventually built up and created a steam pocket. That AND the fan was running slow.

I'd check your voltage at the fans and make sure they're cranked up -- this would show up even if you had a 20% voltage drop - say the alternator is cranking out 14.2V and your fan is only seeing 12V...

There have also been some issues with the water pumps loosing their impellers -- they have broken off right at the shaft - so the pump is turning but there's no water circulation. You should be able to see water circulating in the radiator.

[Vince@Meanstreets]

Is the best way to get air out of the system to jack up the front of the car and run it with out the radiator cap? Should I do this a couple of times over a few days? I don't mind buying a tool if that's what I need...

do you have the air bleed tube hooked up?

and what greg said. also ls is not a reverse flow system. something i learned with gregs issue.

[GregWeld]

LS water flow is IN to the motor from the bottom hose towards the thermostat -- and OUT to the radiator at the top hose.

It's easy enough to check flow with a infrared temp gun.... or even using your hand and feel the hoses. Also use the gun to check for temperature DROP from the top (inflow) and bottom (return) --- on in the case of a crossflow radiator -- side to side --- This should drop 20* or so at idle with the fans running.

Use the gun to check front and back of both heads - near the steam vents (I'm assuming your particular LS model has these).

You can also "crack" the seal on these vents (they're O-ringed) one at a time to see if you can hear or see air (steam) vs water flow etc. The temp gun should also show you a temp differential if there is one...

The very first thing I'd do is to use a temp gun to see if the THERMOSTAT and other areas on the block - are reading the SAME as your TEMP gauge.... In fact - I'd do that before I did anything else.

[Chad-1stGen]

What happens if you rev the motor to 2,000 RPM or above? Will the temps come down at all?

I had trouble getting all the air out of my LS3 also. What I did to finally get all the air out is:

1) Raised the front of the car about 1.5-2 feet on jackstands.
2) filled the motor through the upper radiator hose
3) then filled the radiator
4) Ran the car with the front end still raised and the radiator cap off. With my dual pass radiator is was super easy to look down the open fill and see when the thermostat opened. I allowed the thermostat to cycle open and closed 3 full times with the cap off and then buttoned everything up.

No problems since.

[ErikLS2]

I'm not saying you have air in the system necessarily but if you do, this is a handy tool for filling cooling systems:

http://www.tooltopia.com/uview-550000.aspx

[rkleypas]

I think I made progress last night. I pulled the t stat and it appears to work fine in 160 water. Reinstalled that and filled the system. It got hot with the cap off. I shut it off and lots of steam came out. Filled the radiator and over flow canister and started to get air bubbles out of the overflow. This only started to happen after the cap was back on the radiator. My top hose gets real hot, bottom hose not so much. I'm going to run it when I get home to see if it runs around 160. The overflow bottle was drawing fluid into the radiator After I re capped it. Should I keep coolant in the overflow? I was never able to see coolant moving. It seemed like the hoses were flimsy until I capped it. Lots of info I know so thanks for the help...

[Vince@Meanstreets]

I think I made progress last night. I pulled the t stat and it appears to work fine in 160 water. Reinstalled that and filled the system. It got hot with the cap off. I shut it off and lots of steam came out. Filled the radiator and over flow canister and started to get air bubbles out of the overflow. This only started to happen after the cap was back on the radiator. My top hose gets real hot, bottom hose not so much. I'm going to run it when I get home to see if it runs around 160. The overflow bottle was drawing fluid into the radiator After I re capped it. Should I keep coolant in the overflow? I was never able to see coolant moving. It seemed like the hoses were flimsy until I capped it. Lots of info I know so thanks for the help...

yes, keep the over flow half to 3/4 full when hot.....check the level when cold. You should have fluid in the bottle with a engine cold.
Top off the radiator. Reinstall cap. Run, let it get to normal op temp. Verify the fans run and note temp. See what the bottle level is.

[rkleypas]

Just want to keep this updated. I think the problem is coming from the proximity of the temperature sensor to the header. I'm going to use a spark plug fabric boot to insulate the sensor and see if the temp gauge stops shooting up so high.

[Vince@Meanstreets]

Just want to keep this updated. I think the problem is coming from the proximity of the temperature sensor to the header. I'm going to use a spark plug fabric boot to insulate the sensor and see if the temp gauge stops shooting up so high.

the surface that registers the temperature is in the heat. External heat should not affect, unless you are running a capillary tube style sender.

[rkleypas]

This is the type sensor I have. This is only going to the gauge.

[GregWeld]

Agree with everything Vince said.


Overflow bottle should always have coolant in it.

[Vince@Meanstreets]

This is the type sensor I have. This is only going to the gauge.

Yeah, external heat should not affect that sender. I believe grounding the terminal will show hot on the gauge. Anything touching the terminal or wire? ie burnt wire shirting to ground.

How did you make out with the air and over flow situation?

[andrewb70]

Something that has not been mentioned are the heater core hoses. Are they plumbed to a heater core? Are they getting hot? The LS cooling system needs to have flow through the two hoses for the heater core.

Andrew

[rkleypas]

Andrew, I will definitely check the heater hoses to make sure they are getting hot. I took the car out for a drive in 100 degree Houston humidity yesterday. VA was cranked to the max, The Highway on XM and my wife and I were comfortable. While driving, temp stayed between 170-180. Pulled it into the shop and let it idle for 5 minutes and it hovered at 200. I think the overflow being empty when I started this journey was causing air to get into the system? The overflow is staying 3/4 full, no bubbling back and it seems to be much more stable. I still need to test it more, but I think I'm on the right track. I am thankful for all the help. I'll keep you all posted. Andrew, I'm waiting on the connector to do the PWM, so I'll be in touch soon...

[Chad-1stGen]

Andrew, I will definitely check the heater hoses to make sure they are getting hot. I took the car out for a drive in 100 degree Houston humidity yesterday. VA was cranked to the max, The Highway on XM and my wife and I were comfortable. While driving, temp stayed between 170-180. Pulled it into the shop and let it idle for 5 minutes and it hovered at 200. I think the overflow being empty when I started this journey was causing air to get into the system? The overflow is staying 3/4 full, no bubbling back and it seems to be much more stable. I still need to test it more, but I think I'm on the right track. I am thankful for all the help. I'll keep you all posted. Andrew, I'm waiting on the connector to do the PWM, so I'll be in touch soon...

I'm still curious. With the car sitting still idling once it gets hot, if you bring the RPM's up to 2k+ with the car not moving does it cool off again?

[rkleypas]

Chad,
I still need to check the temp at 2000 rpm. I took it out for a drive last night and it did great. When I got home, I idled it for 5 minutes and it got to 250. Grrr. Fans are running. I'm starting to wonder if the water pump is weak since I could not see any flow in the radiator with the cap off. If I rev it with the cap off and see movement, perhaps the water pump is weak? Something has to explain why it cools perfectly while moving and starts to climb at idle; again, fans are running to the tune of a jet engine.

[Chad-1stGen]

Chad,
I still need to check the temp at 2000 rpm. I took it out for a drive last night and it did great. When I got home, I idled it for 5 minutes and it got to 250. Grrr. Fans are running. I'm starting to wonder if the water pump is weak since I could not see any flow in the radiator with the cap off. If I rev it with the cap off and see movement, perhaps the water pump is weak? Something has to explain why it cools perfectly while moving and starts to climb at idle; again, fans are running to the tune of a jet engine.

2K rpm is just a random number well above idle. The reason I'm pushing is that your symptoms sounds very similar to my own. I also thought weak waterpump and even went as far as to ship it back to the manufacturer to have it tested. Turned out I still had air in the system despite over 2k miles of street driving...

Mine wouldn't get to 250 at idle but it would get to 215/220 at low rpm. I first realized it was engine speed when I downshifted to go pass a car on a steep grade on the freeway. I was cruising along at 70 mph and 1600-1700 rpm in 6th gear. When I got stuck behind a car I quickly downshifted to 4th and passed the car at 3,000 rpm plus. In the handful of seconds it took to pass the car my temp dropped 10* due to the high RPM.

Getting all the air out of my motor wasn't easy.

[dhutton]

Chad,
I still need to check the temp at 2000 rpm. I took it out for a drive last night and it did great. When I got home, I idled it for 5 minutes and it got to 250. Grrr. Fans are running. I'm starting to wonder if the water pump is weak since I could not see any flow in the radiator with the cap off. If I rev it with the cap off and see movement, perhaps the water pump is weak? Something has to explain why it cools perfectly while moving and starts to climb at idle; again, fans are running to the tune of a jet engine.

Sorry for the stupid question, but is your fan turning the wrong direction? Sounds crazy but it has happened before...

Don

[GregWeld]

Chad,
I still need to check the temp at 2000 rpm. I took it out for a drive last night and it did great. When I got home, I idled it for 5 minutes and it got to 250. Grrr. Fans are running. I'm starting to wonder if the water pump is weak since I could not see any flow in the radiator with the cap off. If I rev it with the cap off and see movement, perhaps the water pump is weak? Something has to explain why it cools perfectly while moving and starts to climb at idle; again, fans are running to the tune of a jet engine.



The FANS aren't needed when you're moving.... the airflow thru the radiator is enough.

Are your fans mounted in shrouds? Is there a gap between the shrouds and the radiator? Have you checked the voltage at the fans vs at the alternator?

What fans and how many CFM do they move? Do they both come on at the same time or are they staggered temp wise?

[rkleypas]

I'm going to get a picture of the fans here shortly. I'm guessing that they are turning in the right direction. They should pull air into the engine compartment across the radiator? Is there a sure fire way to get air out of the engine? Like I said before, I will buy the appropriate tool if needed. Pics in a bit

[rkleypas]

Temp dropped 20-30 degrees into the normal range when I revved it to 2000 rpm. Now I have the front end jacked up trying to burp the air out of the system. Fans are pulling air into the engine compartment. Shrouds look good

[cjsgarage]

I have a tool called an Airlift, which is just a fancy venturi vacuum mounted to a radiator. It works wonders for getting air out. If it's worth the 100$, you can get one on a tool truck (SnapOn, Matco, Mac, Cornwell). The other tool I use to help burp air is a funnel that mounts to the radiator fill. I forget its exact name, but it's usually yellow.. sometimes red.. and can be found at auto parts stores. It makes SURE the highest point is the radiator. Subarus, Porsches, BMWs and all kinds of other cars are just as hard to get the air out of.

Fan shrouds make a huge difference. But if you're not pulling enough CFM at idle, you're going to overheat. Make sure you have adequate fans, and make sure they're shrouded.

[cjsgarage]

Oh. And I know it's summer, but I always run the heater when I'm bleeding the cooling system. You don't want an air bubble trapped because your heater core didn't get flow. Some, if not all, of the A/C systems have a heater shut off for when the dial is set to cold. Turning it to hot and turning the blower motor on at least one click should do the trick. Make sure you're getting hot air out of the vents, not cold air. Cold air would point to air in the system.

Something no one has brought up..

is your sender designed for your gauge? It is possible it's not heating up as much as you think. If the sender isn't matched to your gauge, it could have a steeper curve than the one it actually requires. You can buy a infrared thermometer fairly cheap.. and they come in handy for all kinds of stuff.

[rkleypas]

Pic of my fans. Having a hard time getting these sized correctly. As you can see, dual fans, shroud looks good. I think I still have air in the system. Last night I jacked up the front end and ran the engine, this is the first time the lower hose was as hot as the top hose.

[rkleypas]

Better pic of the shroud...

[rkleypas]

Took my car to a local rod shop. They hooked it up to an air lift and they have all of the air out of the coolant system now. They also drilled a small hole in the thermostat? Not sure what that will do, but he said it is running nice and cool now. Thanks for all the help. You guys prevented me from pulling my water pump and doing a ton of unnecessary work.

[Vince@Meanstreets]

Took my car to a local rod shop. They hooked it up to an air lift and they have all of the air out of the coolant system now. They also drilled a small hole in the thermostat? Not sure what that will do, but he said it is running nice and cool now. Thanks for all the help. You guys prevented me from pulling my water pump and doing a ton of unnecessary work.

hole in the t stat body will help release trapped air from behind it. Its an ole school trick.

Remember, if you are ever unsure what your tech is doing please exercise your right to know and ask.

[Chad-1stGen]

Glad you got it sorted out!

[GregWeld]

Took my car to a local rod shop. They hooked it up to an air lift and they have all of the air out of the coolant system now. They also drilled a small hole in the thermostat? Not sure what that will do, but he said it is running nice and cool now. Thanks for all the help. You guys prevented me from pulling my water pump and doing a ton of unnecessary work.



My question is --- did they find air in the system?? From your post I assume they did...


So the small hole in the thermostat was a trick that even some OEM manufacturers did ("high performance thermostats") - but in "most" older motors (SBC and BBC etc) the thermostats where the high point in the system... AIR wants to rise.

The LS thermostat location is LOW.... so unless the air was pushed thru the system to the thermostat - it would be pretty useless IMHO - but certainly doesn't hurt anything.

Regardless of all that -- I'm glad you think you now have it sorted out and it wasn't that big of a deal.

[rkleypas]

Greg, they did find air in the system. Everything is working as it should now. Chad, thanks for getting me on the right track. Revving to 2000 rpm and seeing the temp drop let me know that I had either air in the system or a weak water pump. Your input on your experiences prevented me from wasting time on pulling the pump etc. So, free beer to all who posted on this thread. SEMA???

[T/Aaron]

I've been struggling with this one myself and so I drilled a small hole in the thermostat(I actually drilled a hole in each section as the LS1 has 2 flat areas that change with the temp). Seems to work fine now but will know for certain after a track day of course! Thanks for posting a real problem and seeing it through.

[GregWeld]

I've been struggling with this one myself and so I drilled a small hole in the thermostat(I actually drilled a hole in each section as the LS1 has 2 flat areas that change with the temp). Seems to work fine now but will know for certain after a track day of course! Thanks for posting a real problem and seeing it through.



That was an old school trick to solve for pump cavation.... in other words - it was a bypass to allow some water to flow but also for air to be able to escape. Back in the day the cooling systems weren't "closed" like they are today.

Not saying this isn't something you can do... just saying there was a reason behind it "back in the day". The LS motors have the "steam vents" that are recirculated into the flow.. and the system should be closed to atmosphere via the use of the overflow can. That can should have enough coolant in it to cover the input - and be able to expand and contract without exposing the input tube. When cold - the input tube should be covered with coolant so that it doesn't draw air in as the motor cools down.


The other thing I've seen -- is the use of a radiator design where the return (to the radiator) hose inlet is near the radiator cap. There's a lot of pressure on that cap when the system is in full flow mode!