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sugisan

280z Overheating at low speeds

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sugisan    0
Posted (edited)

Sorry for posting another overheating post. I did some tests and wanted to confirm my suspensions before buying new parts.

I got the Champion 3 row radiator with their electric fans, but I still have overheating issues at idle and low speeds on hot days (+90 deg F). I've tried putting in a 165F thermostat and water wetter, but no success.

The current electric fan has a flow rating of 890 CFM. I currently have two installed with a shroud. I read on another post that these fans don't have enough flow and should get fans that'll give me above 2500 CFM total. 

Before I buy those fans, I did some testing today. I got a cheap 20" fan and put it in front of my car to see if the extra flow will help. These are all at idle and it was about 70F outside. Since it wasn't hot outside, the car didn't overheat with the radiator fans turned on, so I initially turned off all fans to get the car hot.

1. Idle, No fans - Temp increased to 220 F

2. Turned on radiator fan - No change in temp

3. Turned on 20" fan - Temp decreased to 190 F

4. Turned off 20" fan - No change in Temp

5. Turned off radiator fan - Temp increase to 220 F

6. Turned on radiator fan - No change in temp

7. Turned on 20" fan - Temp decreased to 190 F

8. Turned off radiator fan (20" fan still on) - Temp slow increased

9. Turned on radiator fan - Temp went back down to 190 F

 

I should do this when it's hotter outside, but from these results, it seems like a higher flow fans will help and it's not about water pump not being able to flow enough water or something else. 

What do you guys think? Any inputs welcome! Thanks

Edited by sugisan

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McGruber21    0

I was looking at your profile and saw an old post about a leak you had, the image wouldn't load but a member mentioned " Are you sure that's oil?  It looks like coolant, mixed with stopleak.  That's where the big passage is from block to head.  I had a leak there.". Did you ever get this problem fixed? was it oil or coolant? Im just trying to rule any other possible variables out first. My 280z here in Tucson ,where it 110 degree days are normal, never passes 210 even at idle. Stock radiator, stock water pump, stock cooling fan and shroud, I replaced the water pump with an oem part and completely flushed out the cooling system last year. I filled it with coolant and took it to my buddies shop to insure it had no air bubbles in the system. 

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sugisan    0

The head gasket was replaced and hasn't leaked since so I believe it's fixed. It was coolant that was leaking. 

I will get someone to check for any air bubbles in the system. I did all the fixes so I'm not 100% confident about it. Thanks for pointing that out.

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McGruber21    0

You can purchase or get loaned a radiator bleeder kit from Autozone or O'reillys, Ive used one before with great success but I couldn't pass up my buddy's free offer. Make sure you get coolant everywhere in the system including the heater core if you still have one. Check the lines to see if there still is any stopleak type material, that stuff can and will stick everywhere. Was any of the coolant journals blocked or rusted when you replaced the head gasket? Have you replaced the water pump or taken it off to inspect it?

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Chickenman    4

Yes, your two puller fans are basically too small. Adding on the pusher fan didn't help that much because:

 

1: Pusher fans are not as efficient as puller fans. and they tend to block airflow more than Puller fans. 

 

2: You have the two puller fans still in place and their shrouds now blocking the airflow from the pusher fan. 

 

If you really want a good and cheap solution, go OEM. Take a trip to the junk yard and find a mid-90's Taurus fan. These are a single large fan with very efficient S-Blades. they flow about 3,000CFM  and cool 2,000 HP Big Block Chevies with ease. The S-Blades are far more efficient and quieter than straight blades. About $25. You'll need  a relay of course but that's no big deal. 

 

Some are dual speed with a high and a low speed circuit. Those will need two relays. The Taurus fans are also very thin for their size. They use a flat " Pancake " electric motor. 

 

Ford Taurus fan:

 

DSCN1925.jpg

 

Another really good fan is a mid 90's Volvo V70 fan. Very similar to the Taurus and comes with a two speed controller and Relay  pack:

 

https://www.youtube.com/watch?v=-954_wpRWsQ

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Chickenman    4

BTW, nothing wrong with the factory Thermo-Clutch fan. In fact, most mechanical fans ( on any car ) will pull more CFM than even the most expensive Electric fan. Look at the pitch and width of mechanical fan blades. That tells you something.

 

Yes, you do lose a couple of HP. over an electric fan. Important for manufactures trying to meet CAFE numbers. But not as important for street use. The 280Z air condition fan is 8 blades and with the factory shroud cools very, very well. 

 

My 1976 280Z has a three core copper Rad and the factory 8 blade fan and shroud. It has factory AC. I've been in 95 F weather, AC on and in stop and go traffic. Engine Temps never go above 190F ( 180F Stat ). Soon as I start rolling, temps drop to 180F. 

 

That's with a brand new Nissan Atsugi w/pump as well. Some cheap aftermarket w/pumps have inefficient stamped flat steel blades. The factory cast iron blade style flows a lot more water.

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Miles    32
Posted (edited)

First, thanks for  providing data with your question.

 

 

Save yourself a lot of money, and wasted hours researching this,  and go back to stock fan.

Edited by Miles

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sugisan    0

Unfortunately, I got rid of all my stock cooling components after I got the new radiator and electric fan.  :banghead:

My current radiator is thicker so a stock fan no longer fits. I'll look into the Taurus fan and see if that will fit. 

I also recently replaced my water pump with the curved blades type from Paraut. 

Thank you all for the input.

 

Here's the link to the Engine Masters Cooling fan shootout. The results are pretty eye opening.

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Chickenman    4
Posted (edited)

You lose more than a couple horsepower even with a clutch fan....Motor Trend just did dyno testing, google Engine Masters. Would provide a link if I knew how ! With a shroud loses are greater

 

Yeah, I knew it was 10 to 15 HP . It's more than a couple. Problem with the engine Masters test is they don't test the CFM capacity of the fans. Thta is extremely important.as well>

 

They completely ignore the differences at cruise RPM, 3,500 RPM and below. That's where most street cars spend their time. If you look at the charts, the Cruise RPM variance on the first fan was very slight from 3,500 RPM and below.  Dyno doesn't even start til 3,000 RPM. 

 

2: They did the same generalization as I did in saying that Electric fans only put a one or two HP load on the alternator. A good OEM fan such as a Taurus probably pulls a lot more load than that. They should have tested electric fan power draws and CFM values as well to make their test truly accurate.

 

3: They made no mention of the fact that so called flex fans are absolutely useless at High RPM's. They flatten and draw less HP. But they also effectively become a flat 18" Pizza pan placed behind the radiator. Very effective at blocking air flow through the Radiator but not very good for cooling.  Drag Racers love them because thye only run for  10 to 12 seconds flat out.  Any one who Road Races or Hillclimbs knows what a POS Flex fans are  are because they block airflow. Run a Flex fan down the Freeway on a hot day and their poor performance becomes apparent very rapidly. Particularly if you have AC or a marginal cooling system.

 

They do make Killer Ninja Stars though. Look out!! It's Odd Job!!. 

 

4: Personally, on my Race cars  ( Road Racing ) . I never run a fan. No need  to with proper ducting and airflow planning. But on my street cars I will run the stock fan setup 90% of the time. The 280Z  7 and 8 blade fans work very well and are hard to beat for cooling efficiency.

 

Rotational mass and Inertia also comes into play when running a Ramp up RPM  style Dyno run. Thta was not mentioned in the video. It takes HP to accelerate rotational mass. The Thermal clutch fan they tested was an old heavy steel fan blade design. Profile was fairly inefficient as well. Compare that to the much lighter Japanese and European thermal fans with Plastic compound curve blades. Much lighter and much more efficient. Less rotational mass to accelerate = less HP draw shown on a Ramp-Up RPM Dyno run.  I'd like to see some tests on those as well. I'm willing to bet that the HP drop should be less that the heavy domestic fan tested.

 

And if they did a steady RPM test instead of an acceleration test, the HP loss of the heavy steel thermal clutch fan should have dropped as well. juts some food for thought...

Edited by Chickenman

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Chickenman    4

The Taurus or Volvo fan will do the trick. interestingly I am thinking of switching to a Taurus Fan from my stock 280Z 8 blade fan. But not for the reasons you may think. The problem is my car runs at a perfect 180 F most of the time. The 3 core copper Rad is very efficient and the Thermal clutch fan seldom engages. 

 

That becomes a problem with the factory AC system. The Factory AC system has an evaporator that is undersized . As a result you need good airflow through the condenser . But on my car, the cooling system is so danged good that it seldom switches on the Thermal fan at stop lights. When you stop moving you get no airflow from the condenser and the AC goes luke warm. Start driving ( over 30 MPH )  and it gets  freezy cold again . But stop and go downtown traffic becomes a sweat box in short order.  

 

One of the reasons that OEM's use dual  Electric fans is to reduce engine temps when the AC comes on. But the secondary function is to pull air through the condenser when the car is not moving or crawling in stop and go traffic. I'm thinking of switching to a Taurus electric fan, just so I can get some airflow through the condenser in Stop and Go traffic. 

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sugisan    0

Chickenman, I agree with you on the Motortrend Video. It would be nice to see the hp draw based on air flow and electric vs mechanical. 

 

I'm pretty sure the taurus fan will work for my overheating issue, but I'm curious to see if adding a pusher fan to my current setup will work.

It's definitely not the most efficient or cost effective solution for the reasons mentioned above. But it would be the easiest solution because I won't have to remove the radiator. It will be mounted in front of thee condenser so it'll help with the AC as well.

I'll report back after some more hot weather testing before making my decision.

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NewZed    56

You have a thicker radiator, an AC condenser, and a shroud of some kind, with electric fans.  Anything else up there?  Cold air intakes, intercoolers (not clear what engine you're running), horns, alarm systems, spoilers..etc?   Maybe you just have too much area blocked and a too long path for the air to flow.

 

A simple test of coolant flow versus air flow might be to increase your idle speed and see if it overheats faster or slower.  Since you don't have a mechanical fan all you'll be changing is coolant flow rate.

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sugisan    0
Posted (edited)

I have a cold air intake which does cover the top portion of the radiator. 

Wouldn't increasing the idle also increase the number of explosions so it'll give off more heat? 

In the original test I did, putting the 20" box fan in front of the car actually cooled the car so I'm thinking it's air flow issue and not water flow. I will try it though, thanks. 

Edited by sugisan

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Miles    32
Posted (edited)

Have you looked at Flex - A - Lite fans?

 

I am currently using a 3000 cfm fan and Arizona Z Car radiator  to cool a SBC 350.  Runs cool in traffic here in central Cal on 100 + deg days.  The 3000 cfm is what made the difference.

 

 

https://www.flex-a-lite.com/electric-fans.html?cfm_range=10

 

 

 

http://forums.hybridz.org/topic/122990-arizona-z-cars-radiator/

Edited by Miles

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sugisan    0

I have, my friend recommended those to me. Unfortunately, the car only has 2.5" of clearance between the radiator and belts so those will not fit. 

These were on a different post and two of them may do the job as puller. https://www.summitracing.com/parts/spu-ix-30101522/overview/

 

It's been surprisingly cool the past couple days so I haven't been able to do more testing.

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sugisan    0
Posted (edited)

I did some more testing in warmer weather (90ish deg).

With just the radiator fans, the temps stabilized at 210 deg F. (In hotter weather, the temps have gone past 210 F)

With the 20" box fan in front of the car, the temp slightly decreased to 205 deg F.

With the hood opened, the temp went down to 195 deg F.

So it seems adding a pusher fan may not help as much in hot weather. There was a lot of hot air coming from under the car with the box fan on. My thought is that the decrease in temp came from the box fan helping remove hot air from the engine bay, not really from cooling the radiator. I think Chickenman is spot on about the pusher fans.

I also read that the pusher fan should be mounted on the radiator for best performance. Since my car has the ac condenser in front of the radiator, I would not be able to do this and won't be as effective.

Also played around with increased idle, but didn't seem to do much.

 

For now, I decided to replace my current radiator fans with Spal ones https://www.summitracing.com/parts/SPU-IX-30101522

Youtube comparison videos of Spal fans had me sold. 

Thank you everyone for the help and I will report back once the fans are installed in couple weeks. 

Edited by sugisan

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Slowpoke    1

Very curious to see how this goes. I have dual ebay fan setup that i converted to after an IC install. I am becoming more skeptical of these ebay fans... Looking forward to your report on the spal setup.

 

Any way you could report on the amperage draw on your current fans vs the spal?

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NewZed    56

 

With the hood opened, the temp went down to 195 deg F.

 

So it seems adding a pusher fan may not help as much in hot weather. There was a lot of hot air coming from under the car with the box fan on. My thought is that the decrease in temp came from the box fan helping remove hot air from the engine bay, not really from cooling the radiator.

 

Don't forget that if the air in the engine bay is just recirculating through the radiator it won't do much cooling.  A lowered car with a front air dam might not allow the hot air to leave.  Your observation about what happens with the hood open is a clue.  Maybe focus on getting the air out from under the car, or through the hood, or access panels.  You might be just spinning your fan blades otherwise.

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Chickenman    4
Posted (edited)

One other thing to check, although this helps more at HWY speeds. Do you have the engine splash shield installed? These often get removed and never replaced. They have an important secondary function and that is to create a low pressure area at the rear of the motor to pull air out of the engine bay.

 

Regarding hood propped open and Temperature drops. That was a common tweak when racing Z cars. Road Racers discovered a long time ago that Z cars built up too much air pressure in the engine bays and that restricted air flow through the Rad. We used to space the hood up by 1/2" to 1" at the rear with rubber grommets ( Sway bar link bushings ) on the  Hood pins. That trick will work at both high and low speeds. 

 

77 and later 280Z's also added functional hood scoops in an effort to reduce engine bay temps. That was to reduce Vapor lock in the fuel rails, but it also bled of high pressure air and allowed more air flow through the radiator. 

 

Pontiac GTP hood vents look nice. Here are some on my Autocross Camaro. These were very effective at reducing under hood pressure and venting heat. 

 

post-44147-0-53132800-1498244874_thumb.jpg

 

post-44147-0-63215500-1498244889_thumb.jpg

 

 

 

 

Edited by Chickenman

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Chickenman    4
Posted (edited)

More cooling tweaks. Camaro has an open area between nose of car and rad support.  Air could bypass Rad.  Sides of Rad where already " Boxed in from factory and bottom edge has a scoop to direct air upwards from under car. But they left the top wide open. Dumb. 

 

Sealing this area with an aluminium top plate forces all the air to pass through the Rad.

 

The Carb Air Box was sealed to the hood with a functional cowl vent, and yes it worked very well. 

 

post-44147-0-58903100-1498244621_thumb.jpg

Edited by Chickenman

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