LS swap overheating at idle
09-04-2019, 10:45 PM
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LS swap overheating at idle Hey everyone, I recently did an LS swap into my non GM car and I'm experiencing overheating at idle. It's a gen 3 5.3 with fbody front accessory drive, intake, fuel rails etc. running on a FITech standalone and has a pretty mild trick flow 5.3 cam.
If I'm driving it lowers and maintains a decent temp (197-210), which tells me it's not getting enough airflow through the rad. So I pulled off the crappy fans I had on there and put 2 high cfm fans on there and it made no difference. I then threw a large fan on the outside of the rad to help pull air through but that also hasn't done a thing. It's an aftermarket thicker, taller rad than the factory 5.3 uses.
The water pump is pumping and the tstat is opening at 180 degrees. I could see the coolant shooting past the neck, I burped the system 3 or 4 times until I couldn't see any more air coming out of the fill neck. The lower rad hose was warm and the top was very hot. It's a 15lb rad cap, my steam port crossover tube is routed back into the rad. I have my rad fans on a toggle and I've been keeping them on all the time.
The temp does not settle. It will literally keep rising, I imagine until it does serious damage to the engine but I don't let it get that high.
I just rebuilt the engine. Please give me some ideas.
If I'm driving it lowers and maintains a decent temp (197-210), which tells me it's not getting enough airflow through the rad. So I pulled off the crappy fans I had on there and put 2 high cfm fans on there and it made no difference. I then threw a large fan on the outside of the rad to help pull air through but that also hasn't done a thing. It's an aftermarket thicker, taller rad than the factory 5.3 uses.
The water pump is pumping and the tstat is opening at 180 degrees. I could see the coolant shooting past the neck, I burped the system 3 or 4 times until I couldn't see any more air coming out of the fill neck. The lower rad hose was warm and the top was very hot. It's a 15lb rad cap, my steam port crossover tube is routed back into the rad. I have my rad fans on a toggle and I've been keeping them on all the time.
The temp does not settle. It will literally keep rising, I imagine until it does serious damage to the engine but I don't let it get that high.
I just rebuilt the engine. Please give me some ideas.
Last edited by Garage; 09-04-2019 at 10:54 PM.
09-05-2019, 09:56 AM
#2
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Are you using a thermostat designed for an LS engine, or a conventional SBC thermostat? Because of the way the LS water pump housing is designed, it doesn't seem to work very well at directing water flow if you don't have a thermostat with that little spring loaded divider plate.
I had an SBC thermostat in my Mustang swap for a while, and it'd run pretty hot at lower revs and idle, because it seemed like it'd still recirculate a LOT of coolant through the pump even when the thermostat was open. It simply wasn't pulling in fresh coolant from the radiator.
Also, depending on how your heater core works and/or what you've done with your heater lines, that may also be causing you some problems. If you have a heater plumbed in, I think the LS expects that the heater must be "full flow" even when it's shut off. If you do not have a heater, then it is preferred to loop the two ports together, rather than plug them.
I had an SBC thermostat in my Mustang swap for a while, and it'd run pretty hot at lower revs and idle, because it seemed like it'd still recirculate a LOT of coolant through the pump even when the thermostat was open. It simply wasn't pulling in fresh coolant from the radiator.
Also, depending on how your heater core works and/or what you've done with your heater lines, that may also be causing you some problems. If you have a heater plumbed in, I think the LS expects that the heater must be "full flow" even when it's shut off. If you do not have a heater, then it is preferred to loop the two ports together, rather than plug them.
Last edited by lemming104; 09-05-2019 at 10:39 AM.
09-05-2019, 04:58 PM
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I do have my heater lines plumbed to my factory ports and I am using the factory 5.3 tstat with the fbody waterpump. Would the fact that I'm not using an LS sealed coolant reservoir hurt my temps?
09-05-2019, 06:40 PM
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09-06-2019, 01:51 AM
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The fact that you're not "overflowing" into a sealed tank won't directly/immediately affect how well your engine cools. IDEALLY, you'd want to overflow into a sealed tank so that the coolant can be pulled back into the radiator as the engine cools, but (unless my understanding is off - which is always possible!) it just means that you might need to refill your radiator more frequently since the overflowed coolant would remain in the "puke tank" as the engine cools.
The first thing I'd do is to get rid of the pusher fan - all that's doing is adding to your electrical load, & putting a tiny bit more weight in the front of the vehicle. I remember reading somewhere (a while back) that having fans on both sides of the radiator isn't a good idea. It's been a few years, but I seem to recall that somehow they actually worked against each other to some extent, maybe air turbulence or something. It was the kind of tidbit that I would have kept for future reference - the only problem is, the OneNote file where I kept all of that stuff got corrupted, & I lost a crap-ton of good info (including a BUNCH of useful tidbits from this forum)...
Anyway, drop the pusher fan - no OEM setup uses fans on both sides of the radiator, so we should be able to agree that it's not necessary, right??
I'm not an expert, but I'm thinking that it sounds like one of two things - one, either there's an air pocket in the engine somewhere (yes, I know you bled it quite a bit, but air pockets in LS engines are anything but uncommon). The fact that you're using a carburetor-style intake on a Gen-3 engine makes me wonder if maybe you plugged/blocked off the rear steam lines?? If so, you might want to open them back up again & try refilling the block, just in case.
(Ideally with the vehicle's nose pointed up as steeply as you're able to.)The other possibility that comes to mind is that your radiator is sub-optimal. I know that you said it's "bigger/better/etc", but can you maybe provide more specifics?? Single-pass/dual-pass?? Aluminum/Copper/Rusty hammered steel from 1870s railroad tracks??
Is it custom-built for the application, or a junkyard part that happens to fit?? As you probably already know, a GOOD radiator will promote a certain amount of turbulence within the coolant so that it's forced against the outside of the radiator tubes, which enables the greatest amount of heat transfer from the coolant to the air. If the radiator design is older, that may not be as efficient.A few other questions came to mind as I was typing the above...
What KIND of vehicle is it?? A Bonneville streamliner (yes, I'm exaggerating here) isn't going to have enough frontal area for a radiator of any decent size, & something like a Miata or VW Rabbit won't be hugely better...(Of course, if it's a Blue Bird school bus, we'll assume that you have sufficient frontal area...)
Have you confirmed that the ignition timing is correct? What about the air-fuel ratio at idle??
Do you have an A/C condenser in front of the radiator?? If so, what's the spacing?? If it's not pretty close (ideally, no more than 1/2" IIRC), that could cause the airflow between the two to "stagnate" & not flow through the radiator.
Do you know for certain that one of your radiator hoses isn't collapsing? I would imagine you'd probably notice that, but thought of the possibility, & thought I'd throw it out there just in case...
What are you using for coolant?? Green goop? Orange stuff?? Plain H2O? Water wetter, or no??
Having written all that (whew!), it still seems most likely to me to be an air pocket - but please do keep us informed of what you find. Not just for my curiosity (which is now piqued), but for future readers who might have the same problem as well.
Good luck, I hope that this is helpful!!
09-06-2019, 06:46 AM
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Sounded to me like the "normal" (puller) fans behind the radiator didn't seem to be sufficient, so he added a "pusher" in front - please correct me if I've misunderstood.
The fact that you're not "overflowing" into a sealed tank won't directly/immediately affect how well your engine cools. IDEALLY, you'd want to overflow into a sealed tank so that the coolant can be pulled back into the radiator as the engine cools, but (unless my understanding is off - which is always possible!) it just means that you might need to refill your radiator more frequently since the overflowed coolant would remain in the "puke tank" as the engine cools.
The first thing I'd do is to get rid of the pusher fan - all that's doing is adding to your electrical load, & putting a tiny bit more weight in the front of the vehicle. I remember reading somewhere (a while back) that having fans on both sides of the radiator isn't a good idea. It's been a few years, but I seem to recall that somehow they actually worked against each other to some extent, maybe air turbulence or something. It was the kind of tidbit that I would have kept for future reference - the only problem is, the OneNote file where I kept all of that stuff got corrupted, & I lost a crap-ton of good info (including a BUNCH of useful tidbits from this forum)...
Anyway, drop the pusher fan - no OEM setup uses fans on both sides of the radiator, so we should be able to agree that it's not necessary, right??
I'm not an expert, but I'm thinking that it sounds like one of two things - one, either there's an air pocket in the engine somewhere (yes, I know you bled it quite a bit, but air pockets in LS engines are anything but uncommon). The fact that you're using a carburetor-style intake on a Gen-3 engine makes me wonder if maybe you plugged/blocked off the rear steam lines?? If so, you might want to open them back up again & try refilling the block, just in case. (Ideally with the vehicle's nose pointed up as steeply as you're able to.)
The other possibility that comes to mind is that your radiator is sub-optimal. I know that you said it's "bigger/better/etc", but can you maybe provide more specifics?? Single-pass/dual-pass?? Aluminum/Copper/Rusty hammered steel from 1870s railroad tracks?? Is it custom-built for the application, or a junkyard part that happens to fit?? As you probably already know, a GOOD radiator will promote a certain amount of turbulence within the coolant so that it's forced against the outside of the radiator tubes, which enables the greatest amount of heat transfer from the coolant to the air. If the radiator design is older, that may not be as efficient.
A few other questions came to mind as I was typing the above...
What KIND of vehicle is it?? A Bonneville streamliner (yes, I'm exaggerating here) isn't going to have enough frontal area for a radiator of any decent size, & something like a Miata or VW Rabbit won't be hugely better...(Of course, if it's a Blue Bird school bus, we'll assume that you have sufficient frontal area...)
Have you confirmed that the ignition timing is correct? What about the air-fuel ratio at idle??
Do you have an A/C condenser in front of the radiator?? If so, what's the spacing?? If it's not pretty close (ideally, no more than 1/2" IIRC), that could cause the airflow between the two to "stagnate" & not flow through the radiator.
Do you know for certain that one of your radiator hoses isn't collapsing? I would imagine you'd probably notice that, but thought of the possibility, & thought I'd throw it out there just in case...
What are you using for coolant?? Green goop? Orange stuff?? Plain H2O? Water wetter, or no??
Having written all that (whew!), it still seems most likely to me to be an air pocket - but please do keep us informed of what you find. Not just for my curiosity (which is now piqued), but for future readers who might have the same problem as well.
Good luck, I hope that this is helpful!!
The fact that you're not "overflowing" into a sealed tank won't directly/immediately affect how well your engine cools. IDEALLY, you'd want to overflow into a sealed tank so that the coolant can be pulled back into the radiator as the engine cools, but (unless my understanding is off - which is always possible!) it just means that you might need to refill your radiator more frequently since the overflowed coolant would remain in the "puke tank" as the engine cools.
The first thing I'd do is to get rid of the pusher fan - all that's doing is adding to your electrical load, & putting a tiny bit more weight in the front of the vehicle. I remember reading somewhere (a while back) that having fans on both sides of the radiator isn't a good idea. It's been a few years, but I seem to recall that somehow they actually worked against each other to some extent, maybe air turbulence or something. It was the kind of tidbit that I would have kept for future reference - the only problem is, the OneNote file where I kept all of that stuff got corrupted, & I lost a crap-ton of good info (including a BUNCH of useful tidbits from this forum)...
Anyway, drop the pusher fan - no OEM setup uses fans on both sides of the radiator, so we should be able to agree that it's not necessary, right??
I'm not an expert, but I'm thinking that it sounds like one of two things - one, either there's an air pocket in the engine somewhere (yes, I know you bled it quite a bit, but air pockets in LS engines are anything but uncommon). The fact that you're using a carburetor-style intake on a Gen-3 engine makes me wonder if maybe you plugged/blocked off the rear steam lines?? If so, you might want to open them back up again & try refilling the block, just in case.
(Ideally with the vehicle's nose pointed up as steeply as you're able to.)The other possibility that comes to mind is that your radiator is sub-optimal. I know that you said it's "bigger/better/etc", but can you maybe provide more specifics?? Single-pass/dual-pass?? Aluminum/Copper/Rusty hammered steel from 1870s railroad tracks??
Is it custom-built for the application, or a junkyard part that happens to fit?? As you probably already know, a GOOD radiator will promote a certain amount of turbulence within the coolant so that it's forced against the outside of the radiator tubes, which enables the greatest amount of heat transfer from the coolant to the air. If the radiator design is older, that may not be as efficient.A few other questions came to mind as I was typing the above...
What KIND of vehicle is it?? A Bonneville streamliner (yes, I'm exaggerating here) isn't going to have enough frontal area for a radiator of any decent size, & something like a Miata or VW Rabbit won't be hugely better...(Of course, if it's a Blue Bird school bus, we'll assume that you have sufficient frontal area...)
Have you confirmed that the ignition timing is correct? What about the air-fuel ratio at idle??
Do you have an A/C condenser in front of the radiator?? If so, what's the spacing?? If it's not pretty close (ideally, no more than 1/2" IIRC), that could cause the airflow between the two to "stagnate" & not flow through the radiator.
Do you know for certain that one of your radiator hoses isn't collapsing? I would imagine you'd probably notice that, but thought of the possibility, & thought I'd throw it out there just in case...
What are you using for coolant?? Green goop? Orange stuff?? Plain H2O? Water wetter, or no??
Having written all that (whew!), it still seems most likely to me to be an air pocket - but please do keep us informed of what you find. Not just for my curiosity (which is now piqued), but for future readers who might have the same problem as well.
Good luck, I hope that this is helpful!!
The car is a Scion FRS, it's got quite a big opening in the front. No ac condensor, I'm using green coolant 50/50 with water and I did check the rad hoses for collapsing and they seemed good. Timing looked okay and my idle AFR's are sitting at 14.3. I will definitely update here when I try things until its resolved for peoples reference! Thanks!
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09-06-2019, 07:47 AM
#8
How well sealed are your fans to the radiator? If they're not sealed/shrouded properly, they can move all kinds of air, and little of it across the core. If you're cooling at speed with no problems but not at low speed, you've got a problem with air movement. I've got an LS3 in a Volvo 240 -- twin 11" fully shrouded SPAL fans on a variable speed controller. No matter what ambient temps/speed/A-C on/off -- mine sits right at 197F head temps if the t'stat is controlling (under cruise), and about 202F if the fans are controlling (low road speeds). Sure sounds like you're simply not moving enough air with your fan set up.
Strongly suggest you get the fans on some sort of thermal control. At some point, you will forget to switch them on.
Strongly suggest you get the fans on some sort of thermal control. At some point, you will forget to switch them on.
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09-06-2019, 09:53 PM
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How well sealed are your fans to the radiator? If they're not sealed/shrouded properly, they can move all kinds of air, and little of it across the core. If you're cooling at speed with no problems but not at low speed, you've got a problem with air movement. I've got an LS3 in a Volvo 240 -- twin 11" fully shrouded SPAL fans on a variable speed controller. No matter what ambient temps/speed/A-C on/off -- mine sits right at 197F head temps if the t'stat is controlling (under cruise), and about 202F if the fans are controlling (low road speeds). Sure sounds like you're simply not moving enough air with your fan set up.
Strongly suggest you get the fans on some sort of thermal control. At some point, you will forget to switch them on.
Strongly suggest you get the fans on some sort of thermal control. At some point, you will forget to switch them on.
09-07-2019, 04:13 PM
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It's a Blackworks USA 16". I don't know the specs as there is little to no info on it. Worst case if it doesnt cool with the new shroud I will buy new more efficient fans instead. I just hate to spend money on stuff when I don't have to and it could be going somewhere more useful.
09-07-2019, 04:39 PM
#12
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A good fan shroud and a recheck of those rear steam lines mentioned above . . . good advice. Those steam lines are great for purging air pockets out of your cooling system.
Rick
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09-08-2019, 03:39 PM
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The engine came with both rear steam ports plugged with the oem plugs. Only the front had the steam port plumbed.
09-08-2019, 03:51 PM
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Also I was reading another post and a guy asked if the steam ports are supposed to have a steady flow of coolant. The answer was no, they are supposed to only vent air in the coolant jackets with minimal coolant flow. Well I originally had mine vented to the top of my overflow and it filled my overflow up within 2-3 min.
09-08-2019, 09:10 PM
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Also I was reading another post and a guy asked if the steam ports are supposed to have a steady flow of coolant. The answer was no, they are supposed to only vent air in the coolant jackets with minimal coolant flow. Well I originally had mine vented to the top of my overflow and it filled my overflow up within 2-3 min.
09-08-2019, 09:35 PM
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I thought that the Gen-III engines had all four steam ports tied together/in use, but that's just me relying on my memory, so that thought is probably worth what you paid for it...
OK, that's good to know - sure doesn't sound like you need to worry about any air pockets there anyway...
OK, that's good to know - sure doesn't sound like you need to worry about any air pockets there anyway...
09-09-2019, 10:38 AM
#17
Are you absolutely sure the system is burped and free of air? Do you have any photos showing where you are filling coolant and general routing of hoses, etc? Have you tried any IR temp on your radiator to be sure the whole thing is filled and flowing coolant?
Regarding the flow from your steam ports to your overflow, yes they will flow quickly when connected to the overflow, because the cooling system & radiator operate at higher pressure than the overflow. I don't think this is related to your issue.
Regarding the flow from your steam ports to your overflow, yes they will flow quickly when connected to the overflow, because the cooling system & radiator operate at higher pressure than the overflow. I don't think this is related to your issue.
09-09-2019, 03:24 PM
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Are you absolutely sure the system is burped and free of air? Do you have any photos showing where you are filling coolant and general routing of hoses, etc? Have you tried any IR temp on your radiator to be sure the whole thing is filled and flowing coolant?
Regarding the flow from your steam ports to your overflow, yes they will flow quickly when connected to the overflow, because the cooling system & radiator operate at higher pressure than the overflow. I don't think this is related to your issue.
Regarding the flow from your steam ports to your overflow, yes they will flow quickly when connected to the overflow, because the cooling system & radiator operate at higher pressure than the overflow. I don't think this is related to your issue.
09-09-2019, 03:36 PM
#20
Careful about holes/shroud unless they’re flapped. When your fan comes on it will pull air in through the holes and blow it right back to the compartment REDUCING air pulled across the rad. If you’re cooling at speed, but not with the fans on at low speed/stopped you’ve most likely got a fan problem.