Thermostat or restrictor?

[Ned Stevens]

'83 Rabbit GTI that I run in ITB. Currently has a thermostat. Has always run a bit warm-and sometimes hot. What do you guys suggest? Thanks, Al

[shwah]

Properly shroud the radiator to make sure all the air coming in the front of the car passes through the core.

[JamesB]

What are your current water temps running mid race? End of race? I run an mk2 golf in IT prep using a stock 190F T stat with 3x3mm holes drilled into it which drops it to a 170Fish temp (cheaper then buying the lower temp models and you can get one from any store.)

What are your oil temps? Do you run an oil cooler? If so give me a run down on the setup.

[markw]

If you remove the thermostat, you will need to block the hose between the head and the waterpump. The stock thermostat closes the bypass as it opens for the main flow. The thermostat is on the suction side of the pump. Any type of restriction on the suction side of the pump will increase the chances of cavitation. Spinning the pump faster than designed will also cause cavitation. Using a radiator from an 85 golf that came with factory AC is a cheap upgrade. Another mistake I see people make is with the fitting on the back of the cylinder head and the resevoir tank. We run the coolant tme sender in the hose fitting. The resevoir should be plumbed into the middle fitting on the waterpump. This insures all coolant flow is out the head into the top of the radiator. Plumbed this way, it should be self bleeding. Ducting between the radiator and the front grill as the factory did does help. If you find the engine runs too cool, you could fabricate a restrictor to fit under the coolant flange on head. We have not found that we need one in the Southeast.

[tom_sprecher]

Properly shroud the radiator to make sure all the air coming in the front of the car passes through the core.

+1

I don't know about VW's but when I did this and changed the oil cooler location on my RX-7 it eliminated any cooling problems I had except now it may run too cool if there is such a thing on a rotary.

[Sandro]

Shrouding the radiator makes a huge differnce. I have the stock radiator (83GTI) shrouded on all 4 sides with a slightly lower thermostat and a 1/8" hole drilled in it for bleeding the air out. With the new motor before I put the oil cooler on I had temps at exactly 190 never went over even a mm on the gauge and the oil temps were pretty high I also don't run a fan so you get much better flow through the radiator.

[kakarot]

'83 Rabbit GTI that I run in ITB. Currently has a thermostat. Has always run a bit warm-and sometimes hot. What do you guys suggest? Thanks, Al

If you get rid of the thermostat you will run significantly cooler.
The best solution, I would believe is to buy lower temp thermostat. They are not that expensive and defiantly will keep the engine in optimal temp range. Instead of too cool when running at full power without the thermostat.

If I remember correctly, there is a 78C thermostat available. The stock is 92C, I think.

My math I did before is retarded and wrong, but gets the approximate thermostat temp. thermostat temp - (Your normal running speed temp - desired temp)= new thermostat

I remember reading a SAE paper on temp vs power. They suggested to run significantly hotter engine to make maximum power. I think the number was 105C or something. Converting a 90C engine into 105C would require recalculating the clearances.

Most likely I am wrong and forgot the details. Correct me if I am wrong.

[racer_tim]

I run a restrictor plate. Took a thermostat housing, and tore off the spring the perch. End of story. Who cars how long it takes to warm up the water. You need to warm up the oil, brakes, tires, and tranny along with the water, so just take it easy the first couple of laps.

One less thing to fail and/or worry about.


If you get rid of the thermostat you will run significantly cooler. Actually, you will overheat your motor if you remove the thermostat. You need to slow the water down, or it won't cool down enough when it goes through the radiator.

[chewy8000]

It's a little $$$$$$ at $275 but I switched to an AFCO alluminum racing radiator from Summit. It's actually called a "scirocco" style radiator on their website. It runs perfect temps and the dual electric fans are over kill. No shroud needed.

[Lael Cleland]

I run a tworn apart t-stat as a restrictor, and no fan 200F most of the time. less to go wrong. I have had a Whaller t-stats fail at the track. The golf W/ a/c rad works well@ 70-100bucks.........some day an all alluminum rad, after the LSD would be sweet!

[Campbell]

I was constantly running too hot, especially in 90 degree July weather!! I ended up shrouding the radiator (most important), gutted a thermostat to make a restrictor, blocked the water pump bypass hose and the hose going in the side of the head so all coolant goes through the radiator before entering the radiator, put on an oil cooler (2nd most important!!) and eliminated the OE water cooled oil cooler and finally switched to water wetter. I also added a small electric fan for paddock cooling. It runs perfect now. good luck

[racer_tim]

I also "hot wired" the stock fan to a switch on the dash, so during safety car laps, I have to remember to hit the switch, and make sure to turn it off @ speed.

[JamesB]

tim, I have the same setup and added a bright orange LED light to remind me that its on.

[Greg Gauper]

Actually, you will overheat your motor if you remove the thermostat. You need to slow the water down, or it won't cool down enough when it goes through the radiator.
Lots of discussion regarding this over on the 'Open Wheel' site. The consensus is that slowing down the cooling flow to help cooling is a myth. The higher the flow rate, the more effective your cooling will be.

http://www.apexspeed.com/forums/showthread.php?t=29010

Some really good discussion by some very sharp people...particularly Mr. Weitzenhof (7-Time National Champ).

[Sandro]

this past weekend with my setup listed above stock rabbit radiator(new) slightly lower thermostat, no fan and completely shrouded radiator in 100+ weather the temp never even got above 200

[racer_tim]

The fact that IT cars spin revolutions more than "stock" and that in order to slow the water pump down to spin at a more efficient rotation, that's why the larger water pump pulley is the way to go.

The entire reason that a thermostat is on all street cars, is to allow the water to warm up faster, and then with the water temp reaches the t-stat temperature, it opens up and lets water flow through the radiator. We don't need this on a race car.

That's why a restrictor is a good idea. One less thing to fail, and still allows the car to warm up, but not at the same "speed" as with a thermostat.

[kakarot]

Thermostats are one of the things that is reliable. I seen thermostats fail, but those where beaten up and rusted cooling systems. I check all my thermostats, by dropping into a boiling water, and 1 in ~40 was defected.

The conception that at high RPM water is moving too fast was based on truth. Since the water as it goes down the fins of a rad can turn turbulent, losing it's efficiency of cooling. However that concept was true on seriously modified cars. Like NASCAR, they have overdrive system and large rads.

Good thing about production cars, is that its calculated into the development of the cooling system. So the too fast, actually does not happen on most production cars. However, most production cars have a pressure differential to increase the water pump efficiency. Just one of the things to look out for.

[tom_sprecher]

Lots of discussion regarding this over on the 'Open Wheel' site. The consensus is that slowing down the cooling flow to help cooling is a myth. The higher the flow rate, the more effective your cooling will be.

http://www.apexspeed.com/forums/showthread.php?t=29010

Some really good discussion by some very sharp people...particularly Mr. Weitzenhof (7-Time National Champ).

Apexspeed is a great source of general race engineering information and it's where I spent much time back when I was crew chief for a FC team.

[Greg Gauper]

Turbulent flow in the radiator actually increases the rate of heat transfer! Heat exchanger designers actually try to achieve turbulance in the coolant flow as it passes thru the tubes. Turbulance is a function of the tube design and shape.

The only reason to slow down the speed of the water pump is to reduce cavitation....period! It's a band-aid.

NASCAR guys run some very special water pumps with custom impeller designs that allow very high flow without cavitating. From the discussion on the open wheel site by some very savy racecar engineering types:

Quote:
Q = M x C x Delta T

Where Q = rate of heat transfer
M = mass flow rate
C = Constant (specific heat of water) 4.186 joule/gram °C
Delta T = difference between temp out/temp in.

So, increasing flow rate increases rate of heat transfer.

Quote:
That slower flow gives better heat transfer IS an old wives tale. Faster flow always gives better heat transfer, and increased flow also keeps coolant temperature more uniform throughout the system, helping keep the head cool and improving heat transfer at the cool ends of the radiators and the exit of the engine (the front of the head). The old wives tale about slower flow originates from poorly designed flow paths and hot spots inside the engine that exacerbated localized boiling (cavitation), and slowing the flow (while also increasing coolant pressure in the engine) with a restrictor reduced overheating due to reducing that localized boiling. Thus, it was thought (by hands-on, non-engineering types) that slower flow was good. It was actually the increased pressure in the head caused by the exit restriction that was good, NOT the reduced flow (except for the minor effect of reduced cavitation in the head as a result of the slower flow).

Quote:
From the equation above, you CAN'T make the flow 'too fast', you always get better heat transfer with higher flow.

Eventually you would need a pump so big that the engine wouldn't be able to turn it, or the heat generated by the pump would be more than the engine produces, which would skew results somewhat, but I think we can leave those extremes out of this discussion.

Quote:
That is, of course, correct. The coolant flow can NEVER be too fast for heat transfer. The "fly in the ointment" is the engine internal cavitation/local-boiling problem, and as you said, the HP loss from the pump.

This matches my real world observation of heat exchanger designs for the hydraulic industry. More flow will always result in better heat transfer and more cooling.

[Greg Gauper]

More good info here regarding turbulent flow vs laminar flow:
http://www.overclockers.com/articles511/index02.asp

[shwah]

The only reason to slow down the speed of the water pump is to reduce cavitation....period! It's a band-aid.

The other reason is because you have a good enough heat exchanger, and good enough airflow management to not NEED as much flow - so you slow it down to reduce parasitic losses, and free .5hp to get to the wheels.

I run a much smaller crank pully, and somwhat larger water pump pully. My water temperatures stays right at 180 in almost all conditions. My oil cooler holds temps at 220 consistently. I don't know why folks shy away from proper air ducting here - it takes $25 of parts from Home Racing Depot and a day to make it right.

[Greg Gauper]

I agree Chris. I was trying to counter the arguement that reducing the water pump speed to reduce the coolant flow was beneficial. My statement was based on the assumption that one did not have enough cooling capacity. You are correct regarding the 'free' horsepower from reducing the flow assuming you have excess cooling capacity.

Taken a step farther, you also shouldn't run a radiator bigger than necessary due to the added weight up front. Run the smallest, lightest radiator that does the job. As you indicated, by paying attention to the shrouding and air management, you can improve the cooling effeciency further.

That's one of the reasons why I posted a link to the open wheel site BTW. Excess weight and drag are so important to those guys, and they go to great extremes to get the cooling system as efficient/light/streamlined as possible.

One final comment...last month I had my Prod car on the dyno at King Motorsports to prepare for the June Sprints. It was quite an eye opener to discover how critical proper coolant temps were to making the best horsepower. It turned out I was running the car too cool by 10-15 degrees. Every engine is different, but there is an optimum temperature at which you will make the most power. Don't assume cooler is better!

BTW Chris, how did you do on Sunday? I stopped by to chat on Saturday during my off sessions from flagging, but you were never around.

[shwah]

Greg - you are dead on. I considered going with a smaller radiator in my car, but the prospect of a triple digit race weekend keeps me running the big one.

Sorry that I missed you at the track. I was talking to one of the other ITB guys that was solving a problem at the time. What corner were you working?

I ended up 2nd both days. Car was still down on power, but we made headway with it on Sunday, and expect to be back up to speed for the next event. It's a shame that the Miata smashed the right side of the car up so badly on lap one, but it appears that he earned a discussion with the BFS during the race for it...

[Greg Gauper]

I was at turn 2 in the morning for qualifying and turn 3 (Carousel) in the afternoon for the race. It looked kinda crowded out there :D

[shwah]

That is was, but in the end it was a fun race - well as fun as 2nd place can be.:eclipsee_steering: