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Y-TRY
11-21-2005, 07:47 PM
It seems like I've known the answer to this but please refresh me...

...Mark VIII fan, 4-core radiator....

My water temp actually rises the faster I go. Not engine rpm fast, but mph fast. Where I live is pretty hilly and if I put the car in neutral and coast down a hill at, say, 70mph- my engine temps actually go higher.

I can idle all day long in 100-degree weather stoplight traffic and not get over 180-190. But at idle, going downhill, the cooling efficiency actually gets worse.

Seems opposite. You'd think that 70mph winds forced through the radiator would help cool. My diagnosis is that the fan actually gets in the way above a certain air velocity through the radiator.

Ideas? Discussion?

rickk
11-21-2005, 08:14 PM
It seems like I've known the answer to this but please refresh me...

...Mark VIII fan, 4-core radiator....

My water temp actually rises the faster I go. Not engine rpm fast, but mph fast. Where I live is pretty hilly and if I put the car in neutral and coast down a hill at, say, 70mph- my engine temps actually go higher.

I can idle all day long in 100-degree weather stoplight traffic and not get over 180-190. But at idle, going downhill, the cooling efficiency actually gets worse.

Seems opposite. You'd think that 70mph winds forced through the radiator would help cool. My diagnosis is that the fan actually gets in the way above a certain air velocity through the radiator.

Ideas? Discussion?
y-try you have a hot spot . the top of your rad is lower than your water neck
rick kirkindall

paul67
11-22-2005, 10:20 AM
Have you got all the holes filled around the rad so the air can only go through the rad, I had this prob on my 57 chevy what would happen is the air hitting the rad at speed would take the least line of resitance ie go under over or around but not through, as the rad acted like an air dam, but at slow speeds the fan drew the air through , cured it by putting seal between bonnet and rad , the side plates back on and fitted a small spoiler under neath like on the 3rd gen camaro's and trans ams.
hope this is of help paul67

BonzoHansen
11-22-2005, 01:42 PM
There was a thread here (or maybe lateral-g) recently that discussed air reversion at high speed - air couldn’t get through. I notice the LT1 4th gen Camaros actually have opening in the fan shroud, with rubber flaps over them, supposedly for this reason.

Y-TRY
11-22-2005, 03:33 PM
This all makes sense. I actually have a gap along the top and bottom edges of the radiator, between it and the shroud, that I have been planning to put weatherstrip on. All of these are good observations. Thanks for the help.

BigBlockOlds
11-27-2005, 11:45 AM
Could also be that the air can't get out of the engine bay fast enough.

I run the dual fan setup from an LT1 F-body on my '87 Olds. In traffic, it does just fine but get it up to 65-70mph, the temps start to climb. Slow down to 50-60mph and they start to level off again.

When I had a 4" cowl hood on it that wasn't sealed underneath, I never had this problem. It wasn't until I went back to the stock steel hood that I started to get the high speed cooling problem.

engine
12-09-2005, 08:13 PM
I had a problem when running a stock type clutch fan. Below 50mph, temp would stay at 180*, but above 50 mph, temps would rise to 190*. I believe it had to do with fan RPM and air stack up behind the rad. Ever since switching to a Mark VIII, tepms get colder at high speed.

gmachinz
12-10-2005, 09:54 PM
On OEM cars with the Mark VIII's, the computer uses vehicle speed info to allow fan to freespin at higher speeds-with a DC Controller, the sensor measures the inrush air temp. at higher speeds and it gradually ramps down fan voltage so that it too, then basically "free-spins". -Jabin

ProTouring442
09-25-2006, 03:47 AM
Could also be that the air can't get out of the engine bay fast enough.

I run the dual fan setup from an LT1 F-body on my '87 Olds. In traffic, it does just fine but get it up to 65-70mph, the temps start to climb. Slow down to 50-60mph and they start to level off again.

When I had a 4" cowl hood on it that wasn't sealed underneath, I never had this problem. It wasn't until I went back to the stock steel hood that I started to get the high speed cooling problem.


Do you still have the factory air dam (big piece of black plastic attached to the core support) under your car? Those G-Bodies are really bottom breathers, and if that air dam is missing they will overheat at speed.

I don't know what kind of car this post was started about, but this piece of information may apply to it as well. Hope this helps!

Shiny Side Up!
Bill
'72 442 "Inamorata"

CliffS
09-26-2006, 12:03 PM
y-try you have a hot spot . the top of your rad is lower than your water neck
rick kirkindall

Rick,

Is this (hot spot) because air can not escape? Just wondering for a while trying to figure out my heating problem.

BigBlockOlds
09-26-2006, 03:53 PM
Do you still have the factory air dam (big piece of black plastic attached to the core support) under your car? Those G-Bodies are really bottom breathers, and if that air dam is missing they will overheat at speed.

I did have the stock plastic air dam in place. But I have since tore my car competely apart and never did get around to figuring out for sure what my problem was.

70GS455
09-28-2006, 10:49 AM
A coworker here at work (aero type) spent his early years working with OEMs in the wind tunnel to get the correct pressure drop across the radiator at speed so that there would sufficient airflow for cooling.

MonzaRacer
10-31-2006, 01:22 AM
Try this open the back of your hood(ie have it up about an in and see if this helps (if you can).
Your problem is you have no air flow through the engine compartment.
Most people get thier cars down low and then the airflow under the car is goneso you have no vacuum under the car ( not road hugging, sucking affect)to pull the air out from engine compartment.
Some road racers use 1/2 in slots in air dam up close to body to aid in cooling but keep the air dam in play for ground effects.
Some cars have too much air dam too. These deflect the air around the car but then you have a dead air space under hood.
I have actually seen people put aluminum blocks under thier hood hinges to raise them up to open it up so air can flow through the engine compartment.
OH YEAH dont run your fan at highway speed it doesnt help on properly setup cars! The only time a fan really comes into play is if the car over heating or going slow when air flow over the rad is negligible or A/C is on.
Ever wonder why some older electric fan setups have blast flaps on them ,,,,so they could open at speed.
you need air flow through your engine comaprtment either from top or under the car. But i bet your car at higher speeds will really hug the ground.
Good luck and if you have any questions let me know.
Lee Abel
AFTERMARKET PERFORMANCE