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karman1970

Overcooling an engine?

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I’m currently researching potential radiator upgrades for our car.  I ditched the thermostat a long time ago.  No cooling problems on the stock motor, but we are expecting to be making more power in the near future.  Is overcooling really a possibility and what are the long term side effects (assuming oil is hot)?  I’ve heard the drag race crowd say “cold water and hot oil” is the way to go.  Even saw a video the other day testing that theory on a dyno and it seemed to hold true.  Is that just a drag racing thing or does the same apply for endurance racing?  I’ve read dozens of other articles that warn of all the terrible dangers of having an engine too cool.

 

Thanks

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13 minutes ago, karman1970 said:

I’m currently researching potential radiator upgrades for our car.  I ditched the thermostat a long time ago.  No cooling problems on the stock motor, but we are expecting to be making more power in the near future.  Is overcooling really a possibility and what are the long term side effects (assuming oil is hot)?  I’ve heard the drag race crowd say “cold water and hot oil” is the way to go.  Even saw a video the other day testing that theory on a dyno and it seemed to hold true.  Is that just a drag racing thing or does the same apply for endurance racing?  I’ve read dozens of other articles that warn of all the terrible dangers of having an engine too cool.

  

Thanks

 

You running a Honda? Run the stock T-Stat if you are. 

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Honda.  I pitched the T-stat several years ago and it’s been running fine so far.  Less than 200F at COTA all weekend.  Why should I put one BACK in it?

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5 hours ago, Team Infiniti said:

Would love a situation where overcooling were even possible here in the SE

Oh, it's possible in the SE. When I was on JAS we had pulled the T-stats out chasing an issue at one point. Stock radiator and cooling system. We ran 140 degrees at RA. Granted it was below 40 degrees ambient temp. LOL

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I know of a certain e30 that ran crazy rich and made less hp at anything lower than 160 degrees.  We had to tape the front opening up.

 

P.s. overcooling is good because you can then tape up the horribly draggy hole in the front of the car!

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13 hours ago, wvumtnbkr said:

I know of a certain e30 that ran crazy rich and made less hp at anything lower than 160 degrees.  We had to tape the front opening up.

 

P.s. overcooling is good because you can then tape up the horribly draggy hole in the front of the car!

 

Could re-tuning it have solved the rich problem and made more power?  With the stock ECU it's probably still in "warm-up" mode below a certain temp, wouldn't you think?

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^I was in the car - middle of the night at Nelsons.  Combo of the course, temps, humidity, walls of fog and # of yellow flag laps, I had a very hard time keeping the coolant temps above 145~155 degrees.  Different tuning may help but there is still a baseline temp that needs to be there for warm-up.  Car felt sluggish - fat tune type sluggish.  Sure seemed that the car livened up after the tape job at driver change.   I have the data files somewhere, but never looked at them to compare where the lap time difference was coming from.

 

So in short - depending on ECU, potential reduced power and increased fuel consumption if you are running too cold for what the ECU wants.  Thermostat can/will help keep engine temps where the ECU is happy.

Edited by NigelStu
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Didn't Smokey find max power around 200* water temps? I know current NASCAR's run around 230-250* water temp (obviously not apples/apples with a ChampCar).  

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Engines are designed to run at a certain temperature. They design piston-cylinder clearances around thermal expansion at that temperature. The ECU also have fueling and ignition tables that reference coolant temperature. If you have a stand-alone, you are probably alright but it’s usually recommend to design for the target oem temperature. 

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Put a tstat in that beast. Most of the tstats i have seen offer more than enough coolant exchange rate when open. Most cars will cool no better with the tstat open vs removed.

 

Cooling the water lower will make the fuel less likely to be fully atomized, screw with your ecu (potentially fault mode it), often screws with your timing map and will reduce your power output. You want the intake cold but the cylinders hot....if you have a plastic intake this tips the scales back to higher water temp. Lots of drag motors and circle track motors have lots of heat soak into the aluminum manifold which drives them to cooler water...but i assume your motor will not have that level of intake heat soak from the engine (because it is off to the side)

 

Don't forget that if the cylinder is hot it can actually make some power with zero combustion, as the cold intake air warms from the cylinder walls and expands in the chamber just like a combustion event. Small effect, but in the right direction power wise....

Edited by Black Magic
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@wvumtnbkr and @NigelStu are both right. You can over cool and engine if you have a different ECU other than factory. My ECU is setup with a map for warm up until  it hits a certain range then it has another temp range for regular map. I think we know where our ranges are and use tape to fix issues during a race. We had a tstat fail at a race so now I don't use one. 

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2 hours ago, Black Magic said:

Put a tstat in that beast. Most of the tstats i have seen offer more than enough coolant exchange rate when open. Most cars will cool no better with the tstat open vs removed.

 

Cooling the water lower will make the fuel less likely to be fully atomized, screw with your ecu (potentially fault mode it), often screws with your timing map and will reduce your power output. You want the intake cold but the cylinders hot....if you have a plastic intake this tips the scales back to higher water temp. Lots of drag motors and circle track motors have lots of heat soak into the aluminum manifold which drives them to cooler water...but i assume your motor will not have that level of intake heat soak from the engine (because it is off to the side)

 

Don't forget that if the cylinder is hot it can actually make some power with zero combustion, as the cold intake air warms from the cylinder walls and expands in the chamber just like a combustion event. Small effect, but in the right direction power wise....

 

Thanks for all the feedback.  Been running the stock ECU until now, but I picked up a Hondata a few months ago.  I think you can pretty well make it do whatever you want.  Engine is going to get dyno'd and tuned at some point this summer.

 

My question came from watching an episode of Engine Masters and then seeing basically every other reference I could find saying over-cooling is bad and will cost you power and increase engine wear.  Granted, the video was on the dyno vs in a car on track, carb'd vs EFI, and seemed geared toward the quarter-mile crowd, not so much circle track or endurance.  But, the upshot of it was cooler engines have higher volumetric efficiency and make more power.  I stumbled across a thesis paper this weekend that said the same thing, though they were testing a normally aspirated diesel engine at constant load and speed.  It showed that VE and power increase (good) with lower coolant temp, as does BSFC (bad).  Additionally, the video tested intake manifold temp (iced vs heated) and it had virtually no impact on power production.  What DID impact the power was fuel temp.  Cold fuel and cold engine made the most power.  I was wondering whether it was worth it to run cooler than normal and chase a few more ponies, or is there a wear factor associated with a cooler engine that makes it not worth it (assuming oil temp is 200+)?

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1 hour ago, cowboys647 said:

 

Hot fuel, cold charge, hot engine is ideal for combustion. 

Ideal in what way?  Power, thermal efficiency?

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20 hours ago, karman1970 said:

Ideal in what way?  Power, thermal efficiency?

Both. The cool charge has a higher density so you can get as much air in the cylinder as possible, more air more power. The hot fuel warms that charge inside the cylinder causing an increase in pressure which causing an increase of power and efficiency. 

 

I “think” that the hot fuel will also combust quicker and the flame speed will be higher due to less heat needed to combust. I have no quantifiable data to prove this though. 

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1 hour ago, cowboys647 said:

Both. The cool charge has a higher density so you can get as much air in the cylinder as possible, more air more power. The hot fuel warms that charge inside the cylinder causing an increase in pressure which causing an increase of power and efficiency. 

 

I “think” that the hot fuel will also combust quicker and the flame speed will be higher due to less heat needed to combust. I have no quantifiable data to prove this though. 

 

Cold fuel is typically better, as it acts to cool the air and the intake tract in most of our engines (cause we are not direct injection)

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1 hour ago, cowboys647 said:

Both. The cool charge has a higher density so you can get as much air in the cylinder as possible, more air more power. The hot fuel warms that charge inside the cylinder causing an increase in pressure which causing an increase of power and efficiency. 

 

I “think” that the hot fuel will also combust quicker and the flame speed will be higher due to less heat needed to combust. I have no quantifiable data to prove this though. 

Hmmmm maybe I should reroute my exhaust to pre-heat the fuel in the fuel lines.....

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The temperature of the fuel can be a factor but in general it is a small part of what's happening.

 

When fuel is introduced into the incoming air, it's atomized but not fully vapourized. As it turns from liquid droplets to a gaseous form, that phase change absorbs energy. This same process (phase change) occurs in your air conditioning and is what is used to cool the air. Done correctly (ie, strategic placement of fuel injectors), this cooling effect can be used to increase the density of the incoming air/fuel mix and make more power.  

 

The closer the fuel is to its boiling point, the quicker it can go through the phase change, but one has to be careful with carbed engines not to boil the fuel in the lines or the float bowl. EFI can have the fuel temp much higher because of the high pressure lines. I haven't personally done any testing with fuel temps.

 

Direct injection uses very high pressures to both drive the fuel into the chamber against combustion pressure and to much more finely atomize the fuel, resulting in very rapid vapourization. The flame front is more determined by the leading edge interaction of the fuel spray with the surrounding oxygen than by the flame speed of a homogenous mixture, good because the pressure and temp rise in a standard engine would quickly exceed the auto-ignition point of the mix and cause detonation. By controlling the flame front with the fuel spray, 87 octane can safely be used in a 11.5:1 engine.

 

Note that a SIDI engine will have more oxygen in the intake charge because there's no fuel vapour displacing some of the air. That plus the increased compression ratio usually gives up to 10% more power just by itself over a conventional EFI engine. 

Edited by mender
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1 hour ago, cowboys647 said:

I “think” that the hot fuel will also combust quicker and the flame speed will be higher due to less heat needed to combust. I have no quantifiable data to prove this though. 

And I don't think you'll find any. :)

 

By the time combustion starts the bulk of the effect from vapourization will have occurred. From that point, the homogeneity of the mixture will play a bigger part in the combustion process. Typically a stoichiometric mixture will have the highest flame speed, while mixtures on either side will be slower so pockets of less-than-ideal air/fuel mix will slow down the flame front.

 

To make the most power, excess fuel is introduced to ensure that all the oxygen in the intake air is consumed. It also has a cooling effect from the vapourization of the excess fuel and can be a significant factor in controlling temp rise during combustion. 

 

Edited by mender
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We ran in some cool weather at iowa speedway years ago in my d16z6 civic without a thermostat. Ran so cold it went into warm-up mode, and started misfiring under load. Eventually the headgasket blew and we had good reason to believe the running cold/misfiring greatly contributed.

 

I run an OEM t-stat (whenever possible) and change it once a year. Restrictor would probably work too.

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