Why control dual cooling fans seperately?

[JRouche]

JR I am experiencing the same issue as you: 1970 Camaro RS with a GM zz383 properly timed, carbed. Running a large Alumitech radiator and Lincoln Mark VIII fan, 180 Robert-Shaw stat, manual trans.

Driving around town at low speed the engine will be perfect around 185-190, but when I go for a long cruise on the freeway (especially in 5th gear) the engine will be down around 165-170 which is way too cool; you can definitely notice poor fuel atomization occurring. The engine wont tug as hard, especially in 5th gear.


I THINK part of my issue is having a cowl induction hood which is not sealed to the air intake causing extreme airflow through the radiator and out the cowl scoop at 75mph. Since the cowl scoop is above the engine (obviously), all heat rises out. If it was sealed I have a feeling that engine heat would remain trapped under the hood, resulting in more stable temps.

Also possibly running a higher concentration of antifreeze in the coolant (I'm at 30% AF and 70% H2O right now) will reduce its thermal efficiency and get the temps where they should be.

Any ideas and/or insight would be greatly appreciated.
Matt

Oh Cool Someone else with a cold engine.

You might be able to keep some of the heat in the engine compartment by reducing the air flow. Not a bad thought.

But Im thinking it will increase the under hood temps more than getting the block warm. You really want a warm block and the under hood temps cool (specially if you are pulling intake air from inside the engine compartment) .

An internal combustion engine is really inefficient. But, thats what we are working with.

For it to be efficient, meaning fuel use and max power it needs to be really warm, but be able to shed the heat also. Thats where the radiator comes into play. We want the combustion chamber to be pretty hot but not heat soaked.

Ideally it would be a very cold chamber on intake then be a really hot chamber on firing. The perfect engine isnt here yet. But EFI is the closest.

I dont think increasing the under hood temps is a fix.

A happy engine is one that produces ALOT of heat but that can still bleed it off so its not heat soaked. Cool on the outside and warm on the inside.

Ideally its an engine that is really hot running but the cooling system can keep it within a certain temp.

I like to see 185-190 for my EFI engine throughout the driving range.


I dont know. Im ready to install a cooler for an A/C unit next, I need more blockage. My stat is perfect for idling around town, it sets at 180 on the button. But with highway speeds the engine is a lil too cold at 165* JR

[Mr Nick]

JRouche and kryptik - are you guys running a T-Stat bypass from your intake directly to the water pump? If so, that could be enough coolant flow (even with the T-Stat closed) to cause your engines to run too cool at cruise speeds.

Possibly try blocking that temporarily, and running a T-Stat with bypass holes drilled into it (never want zero coolant flow) and see how that works.

[kryptik]

JRouche and kryptik - are you guys running a T-Stat bypass from your intake directly to the water pump? If so, that could be enough coolant flow (even with the T-Stat closed) to cause your engines to run too cool at cruise speeds.

Possibly try blocking that temporarily, and running a T-Stat with bypass holes drilled into it (never want zero coolant flow) and see how that works.

I am not using any dedicated bypass and have a thermostat with no holes. I was under the impression that the heater-core functioned as a bypass, correct me if I'm wrong.

[JRouche]

JRouche and kryptik - are you guys running a T-Stat bypass from your intake directly to the water pump? If so, that could be enough coolant flow (even with the T-Stat closed) to cause your engines to run too cool at cruise speeds.

Possibly try blocking that temporarily, and running a T-Stat with bypass holes drilled into it (never want zero coolant flow) and see how that works.

Im not really sure what you mean about bypass. Im not using any type of bypass. I have a simple coolant system, nuthing fancy. JR

[Mr Nick]

My bad... I was referring to the "J" hose as seen on the below Oldsmobile engine, which allows coolant to skip the T-Stat AND the radiator. This allows flow to prevent hot spots even when the T-Stat is closed. I had a major brain fart, and totally forgot that it bypasses the radiator too, duhhh... I was excited that I might have a solution for you guys, thinking the bypass skips the T-Stat but still flows thru the radiator. False.

Carry on

[H2Ogbodies]

By far the best method I've tried for a more efficient combustion chamber temp as well as increasing power is to allow the fuel to get heated but not over 212 degrees and maintain high pressure and combine that with a very cool air charge. This creates a more vaporous (which is what we all want, right?) mixture which burns much more completely with a lot less hydrocarbons. More of it has to do with thermodynamic efficiency and I have had a lot of success with alternative combustion methods-it has less to do with the overall temperature of the engine and more to do with the temperature of the combustion chamber itself as combustion occurs. I focus on the air charge quality/temperature and the engine temp takes care of itself, providing you don't have any mechanical problems. Are you running a high volume water pump? It could be you are moving coolant too fast thus not allowing enough time for heat transfer through the radiator via your cooling fan.....just a thought.

[nekkidhillbilly]

Thought I'd share some of my experiences with Flexalites, Spal, and now Derale. I ran Flexalites, boy those were terrible! I have a twin turbo setup car and everytime I drove up to the top of Eisenhower tunnel in Colorado (12000ft) I nearly had a heart attack watching my coolant temp push 240. I swapped those gems for some Spals and they worked pretty good. They actually held up to the beating and kept the temps under 210 but had problems when I stomped on it repeatedly. I have a buddy who made a reccommendation on a Derale setup. My first comment to him was Derale's are power suckers and the wiring is as elaborate as a traffic signal. I gave some 16925's a spin and came to find they're really darn quiet and move craptons of air those two little 12"rs moved 4300CFM combined. So far so good... no problems (x-fingers-x). In my opinion they make a really great high displacement radiator fan and they're quiet too! I just used one of their pre-configured relay setups ran a dedicated 30A and am quite happy .

Here's a link with some general info if you fellas are interested. http://www.derale.com/basic/default.aspx

J.

ive used flex a lite on my truck what junk went to derale cheaper and worked 100 times better

[HWYSTR]

You guys that are running too cool may need a second stat, where the coolant EXITS the radiator. The pump is sucking cooled coolant, even though the stat is closed. Might try restricting the exit of the radiator, though careful, go in small steps, may not provide required cooling when it does get hot.

.

[parsonsj]

Another suggestion: get a programmable fan controller with pwm support that will allow variable speed from your fans. Then your fans will run at just enough speed to maintain the temp you want. Add a trinary switch to your A/C and connect it to the override full speed on the controller, and it will go to max speed when the head pressure goes up, then drop when the head pressure drops.

DC Controls has such a controller. It worked perfectly for my Nova.

One other thing: you should use a thermostat at the temp you want the car at for cruising, since usually past 30 mph the car doesn't need any fan.

jp

[HWYSTR]

Another suggestion: get a programmable fan controller with pwm support that will allow variable speed from your fans. Then your fans will run at just enough speed to maintain the temp you want. Add a trinary switch to your A/C and connect it to the override full speed on the controller, and it will go to max speed when the head pressure goes up, then drop when the head pressure drops.

DC Controls has such a controller. It worked perfectly for my Nova.

One other thing: you should use a thermostat at the temp you want the car at for cruising, since usually past 30 mph the car doesn't need any fan.

jp

The issue that's been brought up is the fact that the engine is running TOO cool, on the highway, and at that time, the fans aren't even running. A controller won't help that. Go back through a few of the last posts...

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[parsonsj]

A controller won't help that. Go back through a few of the last posts...

Of course not. That's why the last sentence I wrote above was "One other thing: you should use a thermostat at the temp you want the car at for cruising, since usually past 30 mph the car doesn't need any fan. "

[HWYSTR]

I still don't follow the reasoning. The one poster mentions running a 165-170 on the highway, and is running a 180 stat. How will a controller help that?

.

[parsonsj]

I still don't follow the reasoning.

First of all, I'm responding to the OP's original question: why control the fans separately? My answer: there's another option besides binary control of each of the fans.

Secondly: it's obvious that the thermostat controls the engine temp. If a 180 t-stat results in a 165 temperature, I'd change t-stats. They aren't the most exact devices around. Try a 210.

Thirdly, why all the questions?

[HWYSTR]

Sorry if I offended or irritated, wasn't my intentions at all, I applogize. And I agree, stats don't always operate at the rated settings. Just trying to help, that's all...

.

[parsonsj]

Just trying to help, that's all...

Cool. Me too. It's what makes this site so great.

[BonzoHansen]

I love my DCC controller - using 4th gen fans, damn thing is great. I never hear my fans running and one of them has a growl at full voltage. It did when I put them in 4 years ago and I expected to have to change it. Not yet. If I did not have that I'd have run 3 relays and run them both at 6v at a lower temp and both at 12 volts if it got warmer or AC came on. That is how GM wired the later 4th gens. I’m no engineer, so I figure if GM decided they needed that extra ‘complication’ there must be a reason. Down side is you need 2 fan switches to do that w/o a controller. There is a thread at nastyZ about a dual temp BMW switch that is perfect for it.

I had the exact same issue in my Z with the temps. It would run 150* or less on the highway and perfect 185* at idle/local. Stat was hanging open, and it was a relatively new (~2 years) Robert Shaw type. new stat fixed the issue. Same issue with my DD olds just this fall. New stat problem solved. Just throwing that out there.

[JRouche]

First of all, I'm responding to the OP's original question: why control the fans separately? My answer: there's another option besides binary control of each of the fans.

Secondly: it's obvious that the thermostat controls the engine temp. If a 180 t-stat results in a 165 temperature, I'd change t-stats. They aren't the most exact devices around. Try a 210.

Thirdly, why all the questions?

Hey John. That might have been my post. And like I already wrote. The stat operates like it should with NO air flow through the radiator. Its a 180* stat and it will (along with the electric fan) keep the temps right at 180*, AT A STAND STILL.

When Im driving thats when the temps drop to 165-155*.

If I were to put a 210* stat in Id be idling at the stop lights at 210* (too hot) then cooling off to 165* again (too cold) when Im driving.

Its not the stat, its not the fan, it turns on at 195* on my driveway. I have great temps on the driveway. If I drive it I am WAY too cold, 155* if its warm outside.

Im baffled, the stat should STILL keep the coolant from seeing the radiator if the coolant temps are below the stat opening temps.

And yes, I do still think the stat is the problem. Havent got a chance to swap it out yet. Haven't been driving, working on other parts. The car is on stilts while I make a new exhaust so I can fit my new seats in. How backward is that!! Exhaust, seats? What do they have in common? Clearance. Crazy hobby cars... JR

[parsonsj]

And yes, I do still think the stat is the problem. Havent got a chance to swap it out yet. Haven't been driving, working on other parts. The car is on stilts while I make a new exhaust so I can fit my new seats in. How backward is that!! Exhaust, seats? What do they have in common? Clearance. Crazy hobby cars...

I made headers for II Much so I could locate my floor so I could hang my steering column so I could mount my seats. So I get that.

I think you need to swap the t-stat and then let us know what's going on. Where is the water temp sensor located?

jp

[CarlC]

If the thermostat is closed then the coolant that goes through the heater core re-circulates through the engine. That's why hot air starts coming out before the thermostat opens. The thermostat is the last thing the coolant passes by before exiting the engine side of the coolant pathway. An exception would be if the return from the heater core attaches directly to the return tank on the radiator. You can always wrap the heater hose with a rag and use a pair of vice grips to restrict flow for testing if the car does not have a heater hose shut off valve.

[parsonsj]

If the t-stat is actually closed, there is no way for the radiator to have any significant effect on the engine temp. As Carl says, maybe it's the heater core. I've not ever known a heater core to make 15* difference... but maybe.

Another thought: is the car equipped with an oil cooler? If so, does the oil cooler have a thermostat?

One other thought: it's probably better to have the car idle at 210 and cruise at 180, than to have it idle at 180 and cruise at 160.

jp