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How to exhaust engine compartment heat?

9K views 33 replies 14 participants last post by  red65mustang 
#1 ·
I have a very tight engine compartment, and am looking for ways to exhaust some of the hot air at hwy speed. Car seems to be ok during city driving, but can begin to climb temp wise on the hwy. I figure it is an airflow problem.
I remember reading about “draft tubes” somewhere (not the PCV type) and was wondering if there is any information on them. I have Googled, but come up with engine crankcase breather type tubes.
These are more along the lines of 3” tubes that hang down below the engine compartment and sit in the airflow below the car. The air flowing over the tube cause negative pressure inside the tube, and that helps to suck the air out of the engine compartment. I'm wondering if there is an optimum reverse angle to cut them at to get the maximum effect ? It's kinda like the airfoil leading edge thing.

BTW. I'm running a Ford Taurus 2 spd fan and I have made my hood lovers fully functional, and am sitting on the fence on whether removing the cowl weather strip is helping or hindering. (helps in city traffic, hwy ???)




Thanks
Paul
 
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#2 ·
engine heat.......

HI,why not use the same thing that pontiac and camaros have used for years, its a piece of rubber(bumper material type) that hangs straight down just forward of the radiator. my elec fan went out 1oo miles from home,and i drove my 87 firebird home (on the freeway) without overheating. :) :D
 
#4 ·
boatbob2 said:
HI,why not use the same thing that pontiac and camaros have used for years, its a piece of rubber(bumper material type) that hangs straight down just forward of the radiator. my elec fan went out 1oo miles from home,and i drove my 87 firebird home (on the freeway) without overheating. :) :D
I would like to but my intercooler scoop sits there :-(

dawg
Want to keep the car sleeper looking. Cowl hood would be letting the cat out of the bag. ;-)
 
#6 ·
Since your hood hinges at the front, just lay the hood down without latching it so that the trailing edge sits up above the cowl. Make a highway run with it and see what happens. That will be an easy and no cost way to tell if expelling some of the underhood air in this manner will help.
 
#7 ·
techinspector1 said:
Since your hood hinges at the front, just lay the hood down without latching it so that the trailing edge sits up above the cowl. Make a highway run with it and see what happens. That will be an easy and no cost way to tell if expelling some of the underhood air in this manner will help.
I have tried that by accident, and the hood starts to lift up. I don't know if it is being pulled up by the low psi area neat the cowl, or if it is the exhaust air being forced out of the engine compartment. I don't know if I would want to drive like that unless I had some sort of safety latch.
 
#9 ·
quick72toy said:
I have a very tight engine compartment, and am looking for ways to exhaust some of the hot air at hwy speed. Car seems to be ok during city driving, but can begin to climb temp wise on the hwy. I figure it is an airflow problem.
I remember reading about ?draft tubes? somewhere (not the PCV type) and was wondering if there is any information on them. I have Googled, but come up with engine crankcase breather type tubes.
These are more along the lines of 3? tubes that hang down below the engine compartment and sit in the airflow below the car. The air flowing over the tube cause negative pressure inside the tube, and that helps to suck the air out of the engine compartment. I'm wondering if there is an optimum reverse angle to cut them at to get the maximum effect ? It's kinda like the airfoil leading edge thing.

BTW. I'm running a Ford Taurus 2 spd fan and I have made my hood lovers fully functional, and am sitting on the fence on whether removing the cowl weather strip is helping or hindering. (helps in city traffic, hwy ???)




Thanks
Paul
Every time I look at the picture of the engine compartment, I feel like I just ate a double cheeseburger and super sized fries. How did you get all that in there anyway?

For popping the hood partially open this is a cut and try thing. There is considerable air pressure at the base of the windshield which might actually stall anything from coming out of the gap. This will be a situation that changes with speed probably better function at low speeds than high.

Another trick is to place an air dam under the radiator frame, this will create a low pressure area behind it, which is essentially the engine compartment. This will pull harder on the incoming flow thru the radiator and will tend to create a low pressure area under the hood. This could actually pull some back flow from the high pressure area at the base of the windshield into a gap between the hood and cowl.

Totally crazy would be to plug all passenger compartment connections with the cowl vent. Then put some holes from it's plenum behind the firewall into the engine compartment. At low speed the engine room would vent out the cowl while at high speed the high pressure area would force air in. However, keep in mind that at 100 plus miles an hour the last thing you want is high pressure under the hood, unless you're at V2 and rotating to take off.

I have no idea where you're finding space for 3 inch down tubes, which would work but where are they going?
 
#10 ·
LOL Yeah, she's pretty tight in there. The funny thing is, I have more room to change my plugs than the factory Buick does.

Thanks for the ideas.
Can't do the air dam because the intercooler scoop sits there.
I guess i could pop the hood and put in some sort of safety latch, but I'd like to find another way to get the air out.
The 3" tubes would fit from below. They would go up between the block and frame rails and end just below the headers.
I'm just trying to figure out what angle I should cut the bottom end at.
 
#11 ·
Not sure about the pipe angle. Try using some clear tubing with 1 end in a container of water. Hold the other end at different angles while blowing air across the end with an air blower on air hose. See if it will draw/siphon the water up the tube. May work, may not. :confused: :thumbup:
 
#12 ·
I'm going to mention another possible cause for your overheating at speed.
*
About 25 years ago I put a Ford 302 in my '80 Datsun 200SX.
I had the same problem you've described, overheating at highway speed, but OK at city traffic speeds. I tried adding fender vents, from an early 80's Trans Am, tired taking the hood off, put a smaller radiator in series with the main radiator. (I had an electric fan blowing through the smaller radiator exiting the left front fenderwell.)
What finally cured the overheating was removing the front bumper. It all boiled down to not enough airflow at highway speeds, and the bumper was blocking enough air to cause it. I ended up removing a section of the front bumper and all was well.
Just a thought.
JA
 
#13 ·
quick72toy said:
LOL Yeah, she's pretty tight in there. The funny thing is, I have more room to change my plugs than the factory Buick does.

Thanks for the ideas.
Can't do the air dam because the intercooler scoop sits there.
I guess i could pop the hood and put in some sort of safety latch, but I'd like to find another way to get the air out.
The 3" tubes would fit from below. They would go up between the block and frame rails and end just below the headers.
I'm just trying to figure out what angle I should cut the bottom end at.
I would think that someting from about 30 to a 60 degree angle (long side faoward) would pull a pretty good vacuum with the surrounding air passing by them.

Bogie
 
#14 ·
It looks like I'm going to have to experiment a bit with the angle. Might look up some race car wing designs, and see what info I can find there about optimum angles, negative pressure, and hope I don't get too side tracked. LOL

JA
I hear you about the bumper, but The car would look really funny if I chopped it.
I am making a small scoop/shroud for the front of the rad to try and direct more air into it. I guess every bit helps.


Thanks all.
 
#15 ·
Higher temps on the highway are rarely from underhood heat. They are either from not enough airflow or not enough radiator. I know you're trying to vent underhood air, but rarely is that an issue. The entire bottom of the car is in a pretty low pressure state. Chances are its sucking air out as fast (if not faster) than it can get through the radiator.

Just my 2 pennies.
 
#16 ·
my first thought is:
"fair chance" that your motor does not like whatever your hwy cruise rpm's ign timing is set at and/or the Air/Fuel mix(!) at constant hwy rpms....

if not enough underhood air flow at hwy speed was the problem source it would show up big time in stop and go intown driving!!!....

at hwy cruise rpms the motor is basically "loafing" and only making roughly 60-80HP worth of heat to maintain the hwy speed versus minumum 150HP+ to accelerate from a stop sign....

my point is adding air flow should be your very very last resort....
"something" is generating way way more heat "at" hwy speed than normal.....
don't "engineer your way around the problem" especially since the coolant temp rise indicates the oil is getting hotter than it should "loafing" at hwy speed
 
#17 ·
Well I'm open to all input here, and am getting some pretty good theories.
Because of space issues, I am running a undersized rad for the engine. It has been custom re-cored, with a modern core design, fin count, and larger bottom tank, but I no doubt it is under capacity. The Ford Taurus 2 spd fan (will pull small animals to the front of the car when on high LOL ) makes a huge difference, and running RMI-25 (form of water wetter) and distilled H2O has dropped the temps.

I really think it is an airflow problem. either in, or out. I just thought because of how tight the engine compartment is that air is being trapped in there and somehow at hwy speed it's having a hard time escaping. Could be caused by my low sitting intercooler scoop acting as an air dam and interrupting the below car air flow? I though the draft tubes would counteract the effect of the scoop.

I'm really giving a lot of thought to the idea of not enough air being directed into the rad at speed.

Great point about the AFR and timing at cruise RPM. I am able to alter both. I have the ability to engage a lean cruise mode and set whatever AFR I desire. I may play with a richer mixture to see if it has an effect. I'll have to check what the chips no load timing is set at.

Just to be clear the car does not radically overheat, I just notice that the temp is a bit higher than normal and the fan stays on. If I am cruising at a lower rate of speed it temp is ok, but if I cruise at a higher rate of speed temps will climb a bit. (car is 2800 lbs, fairly aerodynamic, so the load from one mph to the other isn't significant)

I really appreciate all the input.
 
#18 ·
you likely posted the key words in your last post: "undersized radiator"

speaking in the most general terms just for the idea because I don't know how far out of balance your system is:
you will have to increase air cfm thru the to small radiator by a factor of about 4 to equal what just 10% more coolant gpm thru that radiator will do....
the good news is just about any radiator is not operating at it's max possible btu transfer rate based on the normal pump gpm and available air cfm thru the radiator at hwy speed....

simple to test to tell if more gpm thru the radiator/less bypass helps keep the temp stable:
warm the motor up till the thermostat is open then clamp off the pump bypass hose and heater hose so 100% of the pump output goes thru the radiator.....go for a test drive

"fair to good chance" the temp will be stable (small chance the fans will even turn off)

if the test shows good results the simplest fix is change to a high flow thermostat with bypass holes (Stewart) for motor warmup so more gpms are directed to the radiator at normal operating temp

plan "B" is change the pump pulley diameter for a bit more overdrive ratio for more gpm thru the radiator at hwy speed

plan "C" is add a oil cooler.....they do help alot

but...... I would definitely experiment/test the A/F ratio and timing first...
just a 2* timing change can make a 10* coolant temp change....
it is possible the problem is a bit of all of the above (timing/fuel/coolant gpm)
 
#19 ·
Just a bit more background on the setup...
I am running an overdrive pump pulley, flowcooler pump and high flow stat. The Taurus fan pulls around 4500 cfm on high (85A starting draw, 33a continuous)

Just curious... What is the down side to running with the bypass plugged fulltime? (car isn't driven in the winter, so warm up time doesn't come into play)

I used to run an oil cooler, but have run out of locations to mount it. (aux tranny coolers) I do run a dual remote filter setup, so I have upped the capacity slightly, and they sit above an air vent, so there is some cooling effect.

I do have the option of playing with the AFR's and timing, but know a few other Grand national owners who run the same timing and AFR's as I do, and have no heat problems. I don't think there is anything radically out of line at cruise speed, ( timing and AFR wise) but some tweaking may help a bit.
 
#20 · (Edited)
because you have a good pump and overdrive pulley and high flow stat, lack of gpm thru the rad when just cruising is not likely the source of the problem at all....

YUP! you do have a air flow problem!
move the 2 tranny coolers!
(atleast mount them on standoffs forward of the radiator face surface to allow more air to get behind them and thru the rad)....(air will always flow based on the path of least resistance)
as the speed increases the increasing air mass pressure on the cooler faces is mis-directing more and more air from going thru the rad....
it's not over heating in town because the fans can suck hard enough to pull a vacuum thru almost all of the radiator surface

again, just for the idea and from my experience about coolers:
(for the majority of street driven applications), oil coolers and tranny coolers are darn effective/efficent just as long as they do have signifigant ambient air temp cfm flow over them....
(ex: police cars/some big block muscle cars have the oil cooler oem mounted on the upper radiator support to catch air from the hood lip to rad support gap)

do also mount your oil cooler! (as your car is operating now you have "0" cooling reserve capability built in)

possibly behind a hole/gap in the lower apron or on stand offs in front of your intercooler?
"if" you can find room and have a few bucks mount a oil or tranny cooler with it's own cooling fan and thermostat to have the best....max cooling at a stop light and on the road
(kind of a pia and scary as hell to me but coolers "do" get mounted in the wheel wells with stone guards for rocks thrown by the tires)
street rod coolers look like a length of pipe with the fins in the car travel direction so they can be tucked up along the car bottem....

just one of many good reasons to keep atleast one bypass route open is pump bearing life....
at rpms, driving with the thermostat closed, the bypass helps reduce the pump actual operating pressure for less side load on the bearing

one more thing to check:
the dead air space at the top of your custom mount radiator needs to be hopefully atleast 2" above the highest water jacket point on the motor so the system can/will constantly purge any air
CRS=I can't recall if Gand Nationals did have a seperate purge tank system due to rad mount position???

move/change the tranny coolers...the combination of not enough rad tubes and fins area and "lost" air flow thru the rad is killing you (without exellent shrouding your fans are just re-circulating alot of hot engine compartment air)
 
#21 ·
Just another thought (I've been struggling with this issue since I got mine on the road a couple weeks ago) I found the lower radiator hose was collapsing at cruise speed and restricting the coolant flow. Around town it was fine, because the RPMs were lower. I had neglected to put the internal spring in the hose. (so that's what those are for!! :confused: )
 
#22 ·
Re: tranny coolers...
I used to have an tranny intank cooler in the rad, but pulled it out of the rad to lessen some of the overall cooling load, and to increase tank capacity. To supplement the cooling loss, I added a second B&M cooler. (I used to run an large aux cooler that sat under the frame on the passenger side, and ran a fan with it. Look closely below the pass door

It wasn't quite up to snuff during stop and go driving, so I added a second unit in front of it. That helped a lot, but having room restrictions I could only use one fan. Last year I decided to move the smaller of the coolers in front of the rad to sit directly airflow path. Tranny temps are very stable now. If I'm sitting in heavy traffic, I can throw the rad fan on high. works like a charm)

Because of how tight things are I have no room behind the rad for a cooler. Fan - intercooler with shroud - crank mounted intercooler fan. No room between the bumper/grille/rad to mount another cooler. Unable to use a standoff because of the bumper. The only other option is to mount another B&M cooler on the driver side. I'm just worried about the extra load I would put on the oil pump having it so far away. I'm not too keen on having a wheel well mounted cooler.

Rad is mounted above the highest engine water jacket point, so I'm ok there.

"without excellent shrouding your fans are just re-circulating a lot of hot engine
compartment air"
Fan is shrouded well, but I still think if I can cause negative pressure (or at last a balance) in the engine compartment during Hwy cruising it will help to get more air through the rad.
I'll take some pics today so you can get a better idea of what I'm dealing with.


Thought about the lower hose, Had to make custom setup to fit. It is made up of pieces of 2" copper pipe and short lengths of rubber hoses. (no collapse possible)
 
#23 ·
Might need louvered hood to let air out. But it is visible.
I did some louver tests and found that depending on the speed the air might be coming out of the louvers, or going in. Going in at highway speeds is good, it means that there is sufficient vacuum under the car to suck heat out of the engine compartment, although it might lessen the airflow through the radiator. Louvers also reduce heat soak.

Definitely air dams and good core support seals.
Be sure the TOP of the core support seals to the hood.

What type of coolant are you running?
50/50 glycol water mix cools much less than straight water. Consider a test with 20/80 or even 10/90.

Consider Evans Coolant. It works.

It is possible that the water core of the engine has a lot of rust in it. Rust is an insulator.

A radical consideration would be run the heater hose to a remote radiator in the rear of the car. But watch your pump rpm. If you have a heater, try running the heater full blast when the engine gets hot and see if additional radiator area might help.
 
#24 ·
quick72toy said:
LOL Yeah, she's pretty tight in there. The funny thing is, I have more room to change my plugs than the factory Buick does.

Thanks for the ideas.
Can't do the air dam because the intercooler scoop sits there.
I guess i could pop the hood and put in some sort of safety latch, but I'd like to find another way to get the air out.
The 3" tubes would fit from below. They would go up between the block and frame rails and end just below the headers.
I'm just trying to figure out what angle I should cut the bottom end at.
Aerodynamically you want the back cut 30% to the relative airflow, IF the pipes are sufficiently long.
BUT, the question is, what IS the relative airflow direction among all that chaotic air under the car?
Air doesn't necessarily go the direction it looks like it would go. (just like in head ports)
 
#25 ·
POST 17

quick72toy said:
, I am running a undersized rad for the engine.

but I no doubt it is under capacity. The Ford Taurus 2 spd fan (will pull small animals to the front of the car when on high LOL ) makes a huge difference,
and running RMI-25 (form of water wetter) and distilled H2O has dropped the temps.


Just to be clear the car does not radically overheat, I just notice that the temp is a bit higher than normal and the fan stays on.

but if I cruise at a higher rate of speed temps will climb a bit.
.
I apologize. I caught your coolant description this time.

What is "a bit higher than normal"? Running a constant 220 on the highway would not be a problem. If it continues to climb, and never levels off, then you have a problem.

Consider the Evans coolant. It won't boil until 360* and runs only 3 psi radiator cap. http://www.evanscooling.com/main21.htm
 
#26 ·
I have smallish factoryhood louveres, and I imagine they are helping some. I am now working on sealing up the rad, and making sure all the air I can get is directed towards it.
Thanks for the info on the backcut. I'm not sure how the airflow is undernearh the car, i guess it wiil be trial and error with the tubes.
To be honest I guess I really don't have a big problem temp wise. She may hit 185 on a hot day, but the GN setup runs best with a 160 deg stat. I know, I know, before you all start jumping all over me :) This is standard practice for almost all performance GN's. It is one of the first mods that is done. Lower the temp, and you can run higher boost and timing.
I'm also concerned about intercooler heat soak saturation, so if I can drop the underhood temps it is bound to help.
 
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