[gscherer78ta]

I would like your collective thoughts on why this might happen.

Pontiac 400, .030" over with a Lunati 262 voodoo cam and E heads with RPM manifold and Doug's ceramic coated headers. Th350 with 3.23 gears and 18" 275 35 Rival S tires - all meaning that I am running 3100rpm on the hwy. The cooling system is all 4th gen Firebird- Al 2 row radiator, dual electric fans that come on at 195°. The water pump is a Flow Kool high volume pump and I set the divider plate clearance to .025", that was 3 years ago. The cooling system is new this year but, the mechanical fan didn't seem to do much better.

This only happens when it's above 90 ambient temp, or is very humid. I can slow down to reduce the rpm and the fans recover the temp quickly.

[72LuxuryLeMansLa.]

Originally Posted by gscherer78ta

I would like your collective thoughts on why this might happen.

Pontiac 400, .030" over with a Lunati 262 voodoo cam and E heads with RPM manifold and Doug's ceramic coated headers. Th350 with 3.23 gears and 18" 275 35 Rival S tires - all meaning that I am running 3100rpm on the hwy. The cooling system is all 4th gen Firebird- Al 2 row radiator, dual electric fans that come on at 195°. The water pump is a Flow Kool high volume pump and I set the divider plate clearance to .025", that was 3 years ago. The cooling system is new this year but, the mechanical fan didn't seem to do much better.

This only happens when it's above 90 ambient temp, or is very humid. I can slow down to reduce the rpm and the fans recover the temp quickly.

Hot = ?°F

Fans have nothing to do with it at highway speeds except maybe blocking air flow. Do you have all of the factory parts that were designed to direct airflow through the radiator?

[gscherer78ta]

Hot =220+, at least that's my own limit to where I slow down to keep it from going any hotter.

The TA has the factory front spoiler, the core support seems to be original.

I also have a 2002 Firehawk with LS1 that I drive Daily in the same TX heat and it never heats up. No matter how hard it's pushed, with AC on, at idle sitting or running hard on track. Empirically, this leads me to believe the the radiator and fan has sufficient cooling capacity for 360 crank HP and I think that's close to where my 400 is.

I have thought the same thing about the fans running as I'm going down the hwy, before I tried to disable them in that scenario I thought I would solicit other thoughts on the cause. If I believe the radiator and fan have enough cooling then the engine is working harder than 300+ hp, or the water that's coming through the radiator isn't going fast enough to transfer the heat.
If I believe that the engine is only working around 20-40hp while going down the road than either I am not getting enough air to the radiator, or again the water isn't going through the system fast enough.

Other thoughts?

[Ccass]

When you say 220 are you sure? Are you measuring with a mechanical gauge? My TA currently reads 250 when I drive it but it is actually running at 200.

If you are running hot down the highway, I imagine your fans are not turning off? You should have a manual switch to turn them off as the fans are not helping at all at those speeds. They are probably hurting.

You said 2 row but there are big 2 row radiators and small 2 row radiators. What do you have? Increased temps at highway speed almost always mean you have a volume problem. ie; the radiator is too small. (this assumes you don't have any more serious mechanical engine issues.

[Bobalong]

[QUOTE=Ccass;5764624]When you say 220 are you sure? Are you measuring with a mechanical gauge? My TA currently reads 250 when I drive it but it is actually running at 200.

Interesting. How did you measure the temp ?
From what location on the engine?
Mine has hit 230 according to the gauge, never spews.

[Squidward]

I wonder the same about why modern engineered V8's like the LS can run skinny little 2 core radiators and a pair of electric fans all day, every day, and never overheat. My brother runs a 550hp blown LS motor in his sand car, beats on it in the dunes, all with a tilt mounted aluminum radiator running electrics.

I have to imagine there is a lot to do with FI, electronic tuning, and modern engineering design. Maybe the pump flows so much better.

All I know is that not all of the modern platform tricks translate over to our stuff. I have to imagine that it is all about flow through the block, and water pump capability.

[judgeman6970]

Usually, running hot on the hwy is pretty basic. Your engine is making too much heat or your cooling system is insufficient. A big Pontiac V8, running 3100 rpms, depending on timing & mixture, can make some heat. Also, your cooling system could be coming up short. Shrouds, capacity, flow, etc... Gotta start with simple stuff & go from there. Also, imo, tstat & fans should be 180 degress max. g/l!!

[leeklm]

Are you running a vacuum advance on your distributor? If no, you likely should be. The vacuum advance should be adding another 10-15 degrees of advance (somewhere in mid 40s) at cruise rpms. This alone can make a BIG difference in some combos.

Sent from my XT1585 using Tapatalk

[chrisp]

Go up a few #s. in jetting , that will fix it .

[steve25]

Above 30 mph going down the road fans should not be needed on either side of the radiator if your getting the needled water flow thru the Rad and good air flow.

[surfsama]

Originally Posted by gscherer78ta

water that's coming through the radiator isn't going fast enough to transfer the heat.?

I would say the opposite. The engineers design the system to allow heat energy time to transfer at a given rate.

Do you have a thermostat and did you confirm it's operating properly?

[gscherer78ta]

Thanks all! I've been away this last week and am getting caught up.

T-stat always works and start to open at 180 when I pull it and put it in a tub of water and measure the temp with a thermometer.

I think the gage reads accurately because I also compare that to the reading with my infra-red reader, at the t-stat housing and at the rad. (what should the drop be through the radiator?) and they correlate in my garage so I suspect they correlate on the road. So, I believe the engine is getting up to 220 with both the new 4th gen Firebird radiator and the old 4 core radiator I used to have.

I do run vacuum advance, and it's set to 12° off manifold vacuum. The total is set to 34 so when running on the hwy at light loads and high vacuum I would be seeing 46°

[Goatracer1]

I cured all my high temp problems when I installed overdrive in my supercharged GTO. I have 3.89 to 1 gears and the temp now never goes over 180 degrees. Usually runs about 170.

[AdamIsAdam]

I have a long thread on my cooling woes. Short version is this:

1) My engine at 3,000 RPM generates a LOT more heat than at 2,500 and that exposes cooling (and tuning) shortfalls.

2) I messed with my tuning and that did affect things but at 3,000 RPM I was still seeing temps creep up (like you, only at 3,000 and when really hot out)

3) I REMOVED my Taurus electric fan and switched to an 18" 5 blade fan with Severe Duty clutch which I modified the spring to engage sooner. PROBLEM CURED.

Yes, my electric fan was doing more harm than good on the highway.

(I have an aftermarket aluminum radiator of unknown origin, a high flow 160* T-stat. I also run Evan's Waterless Coolant, which will not boil until 375 which gives me comfort knowing I won't boil over. It generates less PSI too (have to change radiator caps) so less likely to spit coolant or blow a hose.

Oh, and I'm not even running a fan shroud! OEM won't fit and I tried it first without any thing. Since that cured it, I left it that way. I run 165 around town, up to 180 if it's 90+ degrees out. On the highway, it'll climb up to 190 or so, but no more. Before, it was hitting 210 or more.

Hope that helps. For many more tips, see the thread I started on this subject.
http://forums.maxperformanceinc.com/...d.php?t=780484

[gscherer78ta]

Thanks for the replies and ideas!

Adam- I'll look into that thread, thank you for your response. I was just reading on your Dyno day and your ET predictions. I had a heavy duty fan clutch, 7 blade fan and shroud and it did better but, not great.

Question: why/where does all the heat from running 3000 rpm come from? Lightly loaded on the hwy I figure these cars need ~20-30HP to run them against the air drag, tires, etc... So, why does the engine work so hard to get down the road?

[chrisp]

Originally Posted by gscherer78ta

Thanks for the replies and ideas!

Adam- I'll look into that thread, thank you for your response. I was just reading on your Dyno day and your ET predictions. I had a heavy duty fan clutch, 7 blade fan and shroud and it did better but, not great.

Question: why/where does all the heat from running 3000 rpm come from? Lightly loaded on the hwy I figure these cars need ~20-30HP to run them against the air drag, tires, etc... So, why does the engine work so hard to get down the road?

Because you are running lean on fuel , go up a few jet sizes & post results .

[gscherer78ta]

Originally Posted by chrisp

Because you are running lean on fuel , go up a few jet sizes & post results .

I've been keeping an eye on this and there is no evidence of running lean. I'm at 900' running a Qjet with #73 jets and CK rods. I've been pulling plugs after every race to check and they all have a nice tan/brown tint to them.

[AdamIsAdam]

I'm watching this thread myself hoping to pick up some tips.

Isn't it possible to run lean at cruising speeds/RPM but not be lean at WOT? If running lean at 3,000 RPM cruise on the highway, you're saying that would cause it to run hotter? But don't modern cars lean out during highway cruising to improve MPG? Don't you want to run as lean as possible provided you can avoid detonation?

(And I'm asking, not telling.) I have read David Vizard's How to Super Tune and Modify Holley Carburetors which goes into great technical detail, much of which is well over my head, but I think he talks about this subject.

Hoping more knowledgeable folks than I will chime in!

[Formulabruce]

Couple notes ( Thoughts...)
Gm did a LOT of research on Cooling as Engines got more and more CR and HP. The ONLY thing a Stock system does NOT account for is the amount of alcohol in the gas now. Alcohol ads many more Octane, but its way less "dense" . Basically this means that your Pontiac WILL run Hotter and Work harder , and run at higher RPM to do the same job it used to.
With E heads, and a 170 T stat ( yes AC Delco makes em) and the original shroud, and HD Clutch on an original Fan it will keep it cool enough. The shroud when engineered allows for an EVEN Vacuum Across the whole radiator. GM tested this with Vacuum gauges placed all around the shroud. The clutch shuts the fan OFF and doesnt interfere with airflow.
Idle circuit ( APT on a Q-Jet) increase of fuel and good clean 3 core radiator with a sealed off wind flow area ( edges of shroud, etc will help. Pontiac issued a defector for Firebirds on the top of the core support too help keep them cool and make sure the fan was pulling through the radiator. I have one of these on my Bird and keeps it as cool as I want to regulate it ( stat)
All Thermostats are rated as "Static" ( in the box, and or just starting to open Temp ). Dynamic T stat ( in running car at temp) is usually 12-15 degrees higher than the T stat rating .
The depth of the shroud and the fan placement in the shroud is as important as the water pump divider plate. Tiny , skinny shrouds with electric fans that dont cover whole radiator are wasting the thermal efficiency of the radiator.. IE Cooling Failure
Last point .. a shocker to many .. The stock cooling set up with a clutch fan and shroud , nets MORE HP than any other set up... Yes there is proof...
Good luck keep that gas from boiling!!

[tom s]

I don't think you can compare anything with new modern computer controlled engines.They were designed to run hotter than our old cars and designed to run on alky-gas.My 455 never gets hot for some reason.Stock firebird 350 radiator and stock shroud with a flex fan.I have never,as in ever checked clearance on my water pumps.Been lucky since 1962.Tom