Engine Asp Pullies Do Cause Overheating Issues

[FastDriver]

Not that I'm breaking any new ground here, but I thought I'd bring it up for posterity. Here are my recent attempts to make underdrive pullies work on my '91 Fox 5.0. I used a centech infrared thermometer aimed at the thermostat housing as my gauge. The IR thermometer is a cheap $30-ish model that reads 203* (off by 9*) when aimed at boiling water. So, it reads a bit low. All future references will be given in gauge readings.

Relevant car setup as purchased: Ron Davis radiator w/o blockage and clean 50/50 coolant, GT40X/GT40/E-303 cam @ 14* base timing. Stock fan & shroud. 180* t-stat. Idle RPM appears to be in the 800-900 range. If you want more info about the car, ask or check out my "new hatchback" thread.

The ASP pullies product description on LRS:
- 2.5" alternator pulley (stock is 2.1" for a 16% difference).
- 15% Water pump under drive (stock is 4.6". This one measured 16.5" circumference so ~5.25" diameter)
- 25% Crank under drive (stock is 5.8" so probably sized 4.375")

Combined, the crank and water pump pullies, as described above, reduce fan and water pump speeds to 63% of stock. If the car is idling at 900 RPM, the adjusted RPM to reach the same fan and water pump speeds would be ~1400 RPM.

I bought the car this way 6 days ago, and drove it for 9 hours without issue. The car averaged 22mpg, despite the 4.10 gears. Temps stayed just above the 2nd white line on the guage while driving, but crept up the gauge in traffic and when idling. I never stopped long enough for it to overheat. I let the car idle on the first day home to see how warm it would get. As a stress test, I put the A/C, which still works wonderfully, on full blast (max) and let it idle in the driveway. The car went right up to 240*, which is my absolute limit with aluminum heads, before I shut it off.

I attempted to fix the problem and retested after each adjustment. First I replaced the fan, which was cracked anyways. With it, I replaced the fan-clutch. No change. Then, I swapped in a 195* T-stat. No change. Finally, today I swapped the water pump with a basic autozone unit.

Today, tests were conducted in 56* ambient temps on a humid overcast day in Xenia, OH. While idling with the A/C off, the car came up to 220*. It's unclear whether this represents an improvement, as the weather today is noticeably cooler than it was several days ago when I initially tested it. Manually raising rpm to 1500RPM -- 1400 RPM was problematic because the computer fought to adjust -- brought temps down to 199* within 5 minutes. With A/C on blast again, the Tstat housing went up to 238*. Concerned, I brought RPM up to 3000, which dropped temps back to 203* within 3 minutes and dropped A/C vent temps down by ~10* immediately.

Despite the fact that I appreciate the looks, extra power and fuel economy, I just can't bring myself to leave these pullies on. A friend of mine already gave me the stock pullies for the alt/WP/crank, and I'm going to put them back on. If/when I upgrade to a 3G alternator & E-fan, I'll give the pullies another chance. Like I said at the beginning, I'm sure I'm not impressing any experienced mustang guys, but it's a bit more scientific a test than I've seen before. I'll follow up with an edit when I swap the pullies over.

- Stock size reference (not sure if correct): Mustang Factory Style Steel Pulley Kit Black (79-93)
- March's pulley kit (for similar sizing information that I couldn't find on ASP pullies): March's Power & Amp Series, with a 4.375-inch crank pulley, a 5.5-inch water pump pulley

Read more: Performance Mustang Underdrive Pulley Test - 5.0 Mustang & Super Fords Magazine
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[liljoe07]

I can see that being more of a problem when the fan clutch is still in use. Doesn't seem to be much of an issue with electric fan setups. I've had under drives for a very long time, but it's always had an electric fan also. Pretty rock solid at 180° even in hot weather.

 

[FastDriver]

Do you have a 2G alternator, and did you catch my comment:

If/when I upgrade to a 3G alternator & E-fan, I'll give the pullies another chance.

 

[liljoe07]

Do you have a 2G alternator, and did you catch my comment:

I had the 2g and electric fans for about 6 years. I've had the 3g for about 2 years.

 

[jrichker]

@FastDriver
Your post is very interesting, thank you for posting it. The real numbers are very useful, it confirms what most of us have thought.

 

[FastDriver]

Well, it might be a bit premature, but I think swapping the water pump pulley back to stock solved my issue. Today it's 54* outside, and after simply swapping my ASP water pump UD pulley back to the stocker, the car has sat in the driveway for the last 20 minutes or so with A/C on full blast and has not gone above 200* as measured at the t-stat housing. 197* with the A/C off.

I suspect I might see issues again in hot weather, but I'd be pretty happy if I could get away with just the water pump pulley. That lets me retain the crank and alternator UD pullies. This means that the water pump is still 25% under-driven due to the Crank UD pulley. If I lost a horsepower or two, big deal.

Yay!

FYI for anyone else who goes through this, with an idler pulley in place of the smog pump, the belt size with all ASP UD pullies was 90.5". With the stock water pump pulley reinstalled, it took an 88.5" belt.

 

[FastDriver]

The saga continues... Today, with 81* ambient temps, the car got up to 225* with the A/C on blast, and 208* without A/C.

Honestly, I want this car to stay where it should stay in 110* weather with the A/C. In record heat or in hot traffic, the car should not overheat. I suspect I'll be able to get there in these ambient temps with the crank pulley, but I'm growing concerned because I don't know how it'll stand up to really hot weather. Hard to believe stock fan and fan-clutch, Ron Davis Radiator, and all new cooling system components aren't enough.

 

[FastDriver]

Disturbing development: The car came up to about 235* with the A/C, and I jumped in, reved it to 3k and the temps only came down 215*. Feeling at a loss for what the problem could be. Kinda hoping there is still an air pocket.

Edit: Hmmff... I dunno. Just took it on a 10-15 minute drive in 5th at 1500-2000 RPM and stayed right where it should've.

I'm swapping the pulley, and we'll see what happens. If that doesn't work, it occurred to me that I should swap the radiator cap, since it's old. I'm not swapping this radiator. That's the only thing left, but I just can't see how it would be the issue. The temps across the radiator while the car is running are pretty consistent.

 

[FastDriver]

After reinstalling the stock crank pulley, I can tell that the fan is moving a lot more air. I don't have time to really test it right, but initial results seem to indicate that the temps are still climbing at idle. Not a happy camper. I suppose it could be the radiator cap, but who knows? I guess I'll try out another radiator cap, but this one worked fine on my other mustang.

Maybe there's a head gasket problem. No white smoke and no fluid where it shouldn't be, but it doesn't make sense that it still seems to be overheating at idle. Now I've replaced:

- fan
- fan-clutch
- T-stat (back to 195* stock)
- water pump
- water pump pulley (back to stock from UD)
- crank pulley (back to stock from UD)

I lost my temp gauge and bought another one. Currently with 79* Ambient temps, the A/C cranking at full blast brings the t-stat housing to 230* F. Turning the A/C off and allowing the car to continue to idle brings the temps back down to t-stat temps. I could definitely tell a difference with how much air the stock crank pulley makes the fan draw, but it's apparently still not enough to bring the temps down with the A/C on.

I'll replace the radiator cap and let it be. It's not worth pursuing to me, anymore. I'm actually ok with 230* temps, but I'm guessing I won't be happy in hotter weather.

 

[jrichker]

All the radiator cap does is allow the cooling system to pressurize the coolant. This raises the coolant boiling point significantly. it does not change the operating temperature of the engine. That is a function of coolant circulation, airflow across the radiator and the ability of the radiator to transfer heat from the coolant to the air that is being forced through it. If you have mechanical problems like leaking head gaskets, dirty cooling system, inadequate coolant circulation, or insufficient airflow, that will cause the engine coolant temperature to be higher than normal.

The A/C has a significant effect on preheating the airflow across the radiator. Refrigerant in the condenser at 250 PSI typically has a temperature of approximately 150 ° F. A wild card scientific guess is that the A/C condenser in front of the radiator transfers about 30° F of this heat to the air flowing though it when the car is parked or moving slowly. It also significantly reduces the airflow volume. Ambient temperature is 80°F + 30°F from the A/C condenser = 110 ° F air temp flowing across the radiator. This represents a significant extra heat load for the radiator to deal with. As the temperature of the airflow across a radiator increases, it loses efficiency in transferring the heat from the engine coolant to the air flowing across it. Simply stated running the A/C makes the engine run hotter. Driving the car at highway speeds with the A/C running moves enough air across the condenser that it doesn't preheat the incoming air to the radiator so much. Less extra heat in the incoming airflow makes the coolant temperature lower.

 

[90sickfox]

I've seen condensors clogged up with dirt and debris.... If you shine a bright flashlight at the back of the radiator you should see the light shine through the fins. There could be areas blocked allowing the rad to heat soak. Just an idea. Timing and lean conditions can also have an influence on engine temps.

 

[FastDriver]

Thanks jrichker. All you said is good stuff. Temps at the condenser were at about 150* as you suspected. I want to say that they were 154* at the hottest point. I guess then, that the answer is that a foxbody with a stock setup cannot idle and run max A/C without experiencing higher temps. I saw it get as high as 245* today, and that's just not going to work. In 100* weather and 265*F+, the coolant is going to boil and temps will spike. I have always been of the impression that aluminum heads should stay below 240*.

I remember having issues with my last Foxbody and struggling to make my black magic fan work, but that was in 90*+ weather, and I didn't care about running the a/c. I would be interested to know if any of you have the same issue at idle with a/c. This to me represents the kind of worst case freeway traffic jam situation in hot weather. I think a car should be able to handle it, but it seems that the foxbody is not capable of it.

@90sickfox, the exterior of the condenser and the radiator are spotless. The coolant in the radiator is perfectly clean.