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2002 WS6 Fresh build: LS2 Short Block, AFR Mongoose LS3 heads, EPS NA LS3 cam, Stock LS3 intake/90mm, 1 3/4” Shorties/High flow y, SLP Dual Dual, T56, 3.73 gear.
Starting out, I understand this set up could be labeled as not quite optimal for most of you and I get that. More cubes, a better cam, and higher flowing intake/exhaust would be a major benefit versus leaving all of that extra power on the table. I needed a set of heads fast and bought them because they were available and would let me grow in the future.
I initially used an LT1 radiator, 160 stat, and 50/50 mix. A motion 4 port steam kit is also in place. The car hit 240+ in 112 traffic with AC on so I pulled off without AC and took side streets home.
After that I installed a set of Dewitt’s fans and went to a 75/25 with water wetter mix. This seemed to help however while working to duplicate the same scenario in 105 degree temps it will still hit 240s sitting in the driveway with AC on idling for 20 plus minutes after a drive with 210-215-225 cruise temps.
Next step was to purchase and install a Dewitt’s 1.25 core radiator. All said and done it is still doing pretty much the same thing however high temps are now 230s. Cruising at 210-215, 225 if I get on it. All temps are via live data and not the factory gauge (which is severely off).
All parts are new, all ductwork and the air dam are in place as intended. I have both vacuum filled and removed air via the steam kit manifold. It will now idle at 185 for 30 minutes plus with out AC running. Am I asking too much of this or could something else be going on? I’d like to keep it below 225 in all situations. Timing or Restrictive exhaust? Thoughts and ideas welcomed.
Last edited by gjohnsonws6; Jul 22, 2025 at 02:50 PM.
All those temps seem completely fine to me. Totally normal. Not seeing a problem here? What's wrong besides some kind of random "I’d like to"?
I started with gen 2 LT stuff years ago and never saw temps this high so I’m not used to it. I assumed after the cooling system upgrades it wouldn’t run this hot.
I've been on a similar quest to you. Fighting heat problems at idle, up to about 35. I 'think' I may have made some progress on mine. Did some logging the other day and the PO jackwad had the idle timing inexplicably cut back so far I'm surprised it ran. Loading up a factory timing table it improved a bunch. It's got some shorties and a baby cam in it but otherwise stock.
But also saw some big drops going to a dewitts rad.
FWY speeds would keep me low 210's w/ the a/c on. But under 35 it would climb up to 240's and start boiling over...
Dewitt rad dropped my moving temps to low 190s, and extended the times I could idle w/ the ac.
Thurs after I bumped the timing back up to stock, I was able to idle about 45min better than half of that w/ the a/c on and seemed to settle about 206. Not been able to drive it to proof off, but that was improvement.
It should NEVER do that. In fact, one of my cars is an 83; it has a stock single electric fan, controlled only by a stock temp switch; the fan DOESN'T EVEN COME ON until the temp reaches approx 234°F (or the AC is on, since the condenser needs the fan regardless of engine temp). All of this is STOCK for 1983.
Everybody likes to chant the sacred mantra "water boils at 212°F". That is ONLY true when THE REST OF the statement is included: "PURE water AT SEA LEVEL PRESSURE boils at 212°F".
The water in a cooling system should be neither pure, nor at sea level pressure. It should be somewhere between 30 and 50% antifreeze, which RAISES the boiling point, just like it LOWERS the freezing point; and it should be at around 15 psi of pressure. Under these circumstances the boiling point is closer to 265°F, maybe more.
Make sure your coolant mixture is correct, and your radiator or coolant bottle cap holds the proper pressure.
It should NEVER do that. In fact, one of my cars is an 83; it has a stock single electric fan, controlled only by a stock temp switch; the fan DOESN'T EVEN COME ON until the temp reaches approx 234°F (or the AC is on, since the condenser needs the fan regardless of engine temp). All of this is STOCK for 1983.
Everybody likes to chant the sacred mantra "water boils at 212°F". That is ONLY true when THE REST OF the statement is included: "PURE water AT SEA LEVEL PRESSURE boils at 212°F".
The water in a cooling system should be neither pure, nor at sea level pressure. It should be somewhere between 30 and 50% antifreeze, which RAISES the boiling point, just like it LOWERS the freezing point; and it should be at around 15 psi of pressure. Under these circumstances the boiling point is closer to 265°F, maybe more.
Make sure your coolant mixture is correct, and your radiator or coolant bottle cap holds the proper pressure.
Yep, by boiling over it was boiling in the overflow under atmosphere at 1200ft. But many parts have been changed since then. This was detailed on another forum, but thought it was interesting this guy is having some very similar problems to what I was having. In the same location/conditions I'm at. Wanted to see what he came up with.
Mine I think (I've not fully tested) was due in large part to the tune that the PO jackwad had in place. Never seen a bad tune have such a huge effect on idle temps.
I've been on a similar quest to you. Fighting heat problems at idle, up to about 35. I 'think' I may have made some progress on mine. Did some logging the other day and the PO jackwad had the idle timing inexplicably cut back so far I'm surprised it ran. Loading up a factory timing table it improved a bunch. It's got some shorties and a baby cam in it but otherwise stock.
But also saw some big drops going to a dewitts rad.
FWY speeds would keep me low 210's w/ the a/c on. But under 35 it would climb up to 240's and start boiling over...
Dewitt rad dropped my moving temps to low 190s, and extended the times I could idle w/ the ac.
Thurs after I bumped the timing back up to stock, I was able to idle about 45min better than half of that w/ the a/c on and seemed to settle about 206. Not been able to drive it to proof off, but that was improvement.
That is the exact information I was looking for. Another thing I forgot to mention is my compression has been lowered due to the bigger AFR head chamber. I believe my tuner has idle timing set at 19 degrees currently. Where are you located?
I took mine out for a test last night (0-20mph) - ambient was only 100. But it's definitely improved. Took it around the 'hood for about 30 mins and it held temps with/without a/c so long as I was moving at all. However, after pulling back in the driveway the temp slowly climbed w/ the a/c on.
It went from about 212 to 221 in 5-10min and as soon as it crested 220 it seemed to 'pick up steam' (pun intended). temps would rise faster, it's always done that at around 220 deg. Gonna have another look through the tune to see if there's something that stands out at that temp.
As far as my tune. I downloaded a copy of the stock 98 (which mine is) and has a more aggressive timing from what I've read from the factory.
the PO dropped the idle speed from 800 to 700
the PO dropped the idle timing from 22 down to 5.. yes 5.. it was very blatant. I have a feeling the PO was trying to get the exhaust note a bit more choppy, which it did... I may bump it a couple more deg as vacuum is a bit low - but the brakes still work.
(the PO tune)
(the stock from hpt repository)
I have the OG LS1 - stock heads, baby cam (comp 54-424-11) as I found out when I did the clutch/back cover a couple of weeks ago, and some shorty headers. As a comparison.
As far as where I'm located - over by Westgate.- Heros Park
I took mine out for a test last night (0-20mph) - ambient was only 100. But it's definitely improved. Took it around the 'hood for about 30 mins and it held temps with/without a/c so long as I was moving at all. However, after pulling back in the driveway the temp slowly climbed w/ the a/c on.
It went from about 212 to 221 in 5-10min and as soon as it crested 220 it seemed to 'pick up steam' (pun intended). temps would rise faster, it's always done that at around 220 deg. Gonna have another look through the tune to see if there's something that stands out at that temp.
As far as my tune. I downloaded a copy of the stock 98 (which mine is) and has a more aggressive timing from what I've read from the factory.
the PO dropped the idle speed from 800 to 700
the PO dropped the idle timing from 22 down to 5.. yes 5.. it was very blatant. I have a feeling the PO was trying to get the exhaust note a bit more choppy, which it did... I may bump it a couple more deg as vacuum is a bit low - but the brakes still work.
(the PO tune)
(the stock from hpt repository)
I have the OG LS1 - stock heads, baby cam (comp 54-424-11) as I found out when I did the clutch/back cover a couple of weeks ago, and some shorty headers. As a comparison.
As far as where I'm located - over by Westgate.- Heros Park
We are definitely on the same page then. I am located in Litchfield Park. Thank you for sharing, a lot of people just don’t understand our situation. I am bound and determined to having everything work correctly with my mods and climate. I have another local friend that swears by his electric water pump…
What cap are you running on the Dewitt’s? I have an 18 psi lever lock. In one of the other recent threads it was mentioned a stock cap should be used instead. I also took mine out last night because it was so nice, I just left the windows down with no AC and enjoyed my drive without fear of overheating and watching the data. Bet it didn’t run over 185 the whole time.
Last edited by gjohnsonws6; Jul 22, 2025 at 03:43 PM.
We're in a pretty extreme climate for sure. Still bugs me that there's problems w/ a relatively minor changes. These cars were tested here in phx - mesa actually at the gm proving grounds. Used to see gm cars driving around the fwy here w/ the manufacturer plates, and rarely but occasionally w/ the body cladding crap on them.
Anyhow, too much waterpump isn't great either. If it doesn't get the dwell time in the radiator, it wont have time to loose the heat as it passes through.
As for the cap, it's literally a factory replacement. non-lever, stock psi. I've not had a boil over for a long time - since I started this saga.
I'd done some testing with the factory fans, as I feel they don't seem to produce what my other cars did. I've got some aftermarket ones in the garage that I'm noodling over putting in, that blow substantially more. Even though I've replaced the motors w/ gm branded ones. I've run them off of a separate 12v power supply and measured the rpm on them at various voltages and it does make a difference. A few hundred rpm between say 12.5 and 14.1v. So there's possibly a component of the cars electrical at play there. I'm pulling about 13.6v at the batt after warmed up and everything drawing on it. which ends up about 13.3 at the fan connector.
If you were at 185 the entire time, that's not bad at all. Your problem is pretty much just w/ the a/c on correct? Have you checked the pressures on your a/c?
We're in a pretty extreme climate for sure. Still bugs me that there's problems w/ a relatively minor changes. These cars were tested here in phx - mesa actually at the gm proving grounds. Used to see gm cars driving around the fwy here w/ the manufacturer plates, and rarely but occasionally w/ the body cladding crap on them.
Anyhow, too much waterpump isn't great either. If it doesn't get the dwell time in the radiator, it wont have time to loose the heat as it passes through.
As for the cap, it's literally a factory replacement. non-lever, stock psi. I've not had a boil over for a long time - since I started this saga.
I'd done some testing with the factory fans, as I feel they don't seem to produce what my other cars did. I've got some aftermarket ones in the garage that I'm noodling over putting in, that blow substantially more. Even though I've replaced the motors w/ gm branded ones. I've run them off of a separate 12v power supply and measured the rpm on them at various voltages and it does make a difference. A few hundred rpm between say 12.5 and 14.1v. So there's possibly a component of the cars electrical at play there. I'm pulling about 13.6v at the batt after warmed up and everything drawing on it. which ends up about 13.3 at the fan connector.
If you were at 185 the entire time, that's not bad at all. Your problem is pretty much just w/ the a/c on correct? Have you checked the pressures on your a/c?
I have not checked draw however I was also at 13.6 volts with stock fans on high so I’d assume that would put me in the same range. My idle voltage with fans on low was at 14.8-9, I have a mechman 170 amp alternator with 2 ga. block grounds/starter, and 4 ga alternator/fuse block supply.
My next move will be to install heavy duty fan relays and get rid of the connectors to eliminate any future problems there. The Dewitt’s 12” Spal paddle fans move 3,280 CFM and I could never find a definitive answer as to what the stock fans actually flow.
I also have a new pair of brushless 12’s Spals but I am not going to touch them because they belong to my turbo car and it would require making a mounting riser as well but I have thought about it. If I did anything different I’d probably go with the Spal turbo blades which would would put out 3,740 cfm.
I will definitely check AC pressure and that is correct my problem only occurs with AC on (with the Dewitt’s not the LT1) so thank you for the tip. I did my recharge with a small vacuum pump since our shop unit was down.
If it doesn't get the dwell time in the radiator, it wont have time to loose the heat as it passes through.
Myth
Not sure why this just won't die. It's FREAKING BACKWARDS.
The Deal is, coolant (or any other material) has a property called specific heat https://www.engineeringtoolbox.com/h...ity-d_338.htmlhttps://www.engineeringtoolbox.com/s...ity-d_391.html, which is, the amount of heat energy it takes to raise the temp of a given mass of it, by a specific amount. Water has a very high value for this, which is convenient for us car people. Which means of course, that the higher the mass (and since water is incompressible, that's essentially the same thing as flow volume) flowing around, the more heat it can move. If the coolant moves slowly, the coolant coming back from the rad is relatively cool, and the coolant in the heads gets relatively hot, which kinda defeats the whole purpose. Or, the faster the coolant moves, the less temp difference there is from the hottest place (head castings) to the coolest (cold side of the rad), since it acquires heat energy from the castings while it's in those, and heats up accordingly (energy divided by mass), then expels the heat into the world at large via the rad; the temp throughout the system is more nearly the same. Instead of very hot heads and very cool return coolant, you have moderately warm heads and moderately cool coolant.
The thermostat limits the flow in any case. THIMK: if the coolant coming out of the heads is hotter than the T-stat set point (i.e. cooling isn't adequate at the moment) it opens, letting MORE coolant FLOW THROUGH, and thus COOLING MORE. IF the MYTH was true, then the engine would run cooler if the thermostat was partly closed, no??? Well, IT DOESN'T work that way, as we all know. Therefore the MYTH can't be true.
By that logic there's never any downside to increasing the pump. So you could have the biggest, super duper pump on a car and it will run the temp at just above ambient temps. Except that the thermostat is going to restrict that flow anyhow. And restricting an overly large pump is going to cause problems of it's own, to include cavitation (which diesel owners know well), and frictional heating (like torque converters - yes it's an extreme example but still true).
Bigger radiators remove more heat in part by having any piece of water spend more time releasing it's heat. Yes, it's less efficient the longer it's in there, but it's still releasing heat.
My point is there's a goldilocks approach to the needed amt of flow, and that going bigger on the pump isn't always better.
there's a goldilocks approach to the needed amt of flow
True, as far as it goes. If your flow is already "adequate", you could double it or mulitply it by 10 or whatever, and gain little or no further useful cooling.
going bigger on the pump isn't always better
Also true, as far as it goes. For many of the reasons you stated. Butt NOT because a bigger pump won't cool as well, and NOT because it doesn't spend enough time in the rad.
Bigger radiators remove more heat in part by having any piece of water spend more time releasing it's heat.
Partially true. They also remove more heat by exposing the coolant to more air flow. They also DO NOT make their improvement by simply slowing the coolant down. That is, a bigger radiator with the water spending the same amount of time passing through it, say one twice as big with twice as much flow through it such that each water molecule spends the same # of seconds in it, will be able move twice as much heat, ceteris paribus.
If it doesn't get the dwell time in the radiator, it wont have time to loose the heat as it passes through.
OTOH, this is ALWAYS false. This particular universe simply doesn't work that way. QED. Maybe the universe you live in is different; butt in this one, this MYTH is FALSE. ALWAYS.
I have thought about that and even have a brand new pair sitting however they are for my turbo car and I will also have to fabricate a riser for the shroud. That being said I’d like to avoid that. At this point everything is working fine until I turn on the AC.
So worth it...I got some from a Chevy volt at scrap yard cheap... went from running hot in stopped traffic to now they only run for a minute or so before they shut off
OP, just checking in to see if you made any progress.
I tentatively think I've got mine straight. Haven't been out at 115, but at 105 a couple of times and it's behaved on my 'gauntlet', the road that pretty much always makes it get hot.
The new fans move a bunch more air, but drug down my alternator, so found a local shop selling high output alternators and that's keeping up w/ the demand.
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2002 F Body Running Hot 
