LS swap overheating at idle
Thread Starter
Teching In
Joined: Jan 2019
Posts: 14
Likes: 0
From: Caledonia, Ontario
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.
"....loads of air...." measured by feeling it with your hand really doesn't tell us anything about the fan's capabilities. I asked above -- thanks for answering about brand. Were specs provided -- CFM at a certain pressure drop and amperage load? That's the kind of data that folks can use to help you know if you've got a capable fan. I've never heard of that type of fan; of course, that doesn't mean anything. The aftermarket is chock full of what I'll call 'no-name' fans that are dirt cheap and buyers find out the hard way that they won't move nearly enough air to keep things cool. If yours is still cooling at speed and overheating at low speeds, I still suspect the fan isn't moving enough air.
What I do know is that folks that use OEM fans (e.g. - Taurus V6, Lincoln Mk Viii, SN95 Mustang, etc.) or those made by companies who manufacture for the OEM's (like SPAL for example) don't have low speed overheating problems that are caused by too little cfm from the fans.
What I do know is that folks that use OEM fans (e.g. - Taurus V6, Lincoln Mk Viii, SN95 Mustang, etc.) or those made by companies who manufacture for the OEM's (like SPAL for example) don't have low speed overheating problems that are caused by too little cfm from the fans.
TECH Regular
Joined: Dec 2011
Posts: 420
Likes: 115
I swore posted on this, but I don't see it.
How is your idle timing looking? That can cause overheating. My understanding is if the timing is wrong either way, it can contribute, but if it's too retarded, it burns in the chamber after the piston's moved down, and the engine absorbs more of the heat, than if it burned while expanding.
How is your idle timing looking? That can cause overheating. My understanding is if the timing is wrong either way, it can contribute, but if it's too retarded, it burns in the chamber after the piston's moved down, and the engine absorbs more of the heat, than if it burned while expanding.
I have an LS swapped 87 Monte SS and had the same overheating issues at idle. I have since fixed the issue with a combination of things that I think are essential in every swap after chasing this issue for a long time.
1) drill 3 small holes in the thermostat to allow warm water in behind the t-stat (used in case the t-stat doesn’t want to open due to air bubble or some other event)
2) f body fans with shroud.
3) loop the water pump inlet/outlet, do not cap them if you don’t have a heater core
4) fill the engine with coolant first through the top radiator hose until coolant starts coming out of the top radiator inlet then put the hose back on the radiator and finish filling the radiator. This gets most bubbles out.
The MCSS doesn’t have great airflow to the rad but this setup does not go above 203* at idle on a 90* day.
Derek
1) drill 3 small holes in the thermostat to allow warm water in behind the t-stat (used in case the t-stat doesn’t want to open due to air bubble or some other event)
2) f body fans with shroud.
3) loop the water pump inlet/outlet, do not cap them if you don’t have a heater core
4) fill the engine with coolant first through the top radiator hose until coolant starts coming out of the top radiator inlet then put the hose back on the radiator and finish filling the radiator. This gets most bubbles out.
The MCSS doesn’t have great airflow to the rad but this setup does not go above 203* at idle on a 90* day.
Derek
Staging Lane
Joined: Apr 2017
Posts: 87
Likes: 0
From: Tulsa, Oklahoma
Something simple you might try is to remove the thermostat completely and see if the problem goes away.
Not saying to drive it all over the place without the thermostat, just remove it and let the car sit and idle for a while to see if the problem goes away.
If it still gets too hot I would suspect the radiator capacity is insufficient or the air flow thru the radiator is insufficient.
If it idles for a while and the temperature is acceptable you have tied it into being thermostat related.
Not saying to drive it all over the place without the thermostat, just remove it and let the car sit and idle for a while to see if the problem goes away.
If it still gets too hot I would suspect the radiator capacity is insufficient or the air flow thru the radiator is insufficient.
If it idles for a while and the temperature is acceptable you have tied it into being thermostat related.
TECH Fanatic
Joined: Dec 2017
Posts: 1,467
Likes: 265
From: Bossier City, Louisiana
If raising the RPM brings the temperature down, that to me means that you are water pump constrained. See if the people at "FlowKooler" have a high volume pump for your application.
Rick
Rick
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Several things here with both to look into..
The Steam Port Line needs to go somewhere that the coolant can go back into the normal loop of flow, not to the overflow tank.
Make sure you have a decent size Radiator and Fans behind it that are properly shrouded to pull a good amount of air through the Radiator. Having a Fan stuck right on it doesn't do much, look how they are setup from the factory.
Never heard of a "constrained" water pump, I've used stock pumps for all the swaps I've done with no issues. Raising the RPM gets more flow from the Radiator most likely, that's where the cooler temp Coolant is and the heat transfer can happen more than just at idle.
Also as mentioned, bleed out the air completely. Sometimes these are a little tricky.
The Steam Port Line needs to go somewhere that the coolant can go back into the normal loop of flow, not to the overflow tank.
Make sure you have a decent size Radiator and Fans behind it that are properly shrouded to pull a good amount of air through the Radiator. Having a Fan stuck right on it doesn't do much, look how they are setup from the factory.
Never heard of a "constrained" water pump, I've used stock pumps for all the swaps I've done with no issues. Raising the RPM gets more flow from the Radiator most likely, that's where the cooler temp Coolant is and the heat transfer can happen more than just at idle.
Also as mentioned, bleed out the air completely. Sometimes these are a little tricky.
Last edited by the_merv; Jun 20, 2024 at 05:34 PM.
On The Tree
Joined: Jul 2013
Posts: 196
Likes: 55
Tagging onto the above comments. I’ve had good luck getting most of the air out of these motors by filling them through the upper radiator hose. I’ve heard of people burning fresh builds down due to air being trapped.
