Grill Block vs. clutch fan

[JeffD]

I installed an upper grill block on my truck. Prior to the grill block the water temperature was running in the high 170's according to the scangage. With the grill block, the water temperature is running in the low 180's even when the weather outside is in the 90's. I don't think I've hit the full open temperature of the thermostat yet. The first inclination is that I can block off more of the radiator, I don't know the temperature that the fan clutch kicks in, but I wonder if blocking the grill is a zero sum game: you get better aero, but lose on the fan. I know the answer is an electric fan, but for now.... I can turn the fan with the engine not running, but I'm thinking that it's turning all the time due to viscous forces anyhow.

The second question I'm sure will get me some raspberry's, but I do use the AC . If I block off the cooling to the radiator (or get an electric fan set to water temperature) I'm afraid I'll loose efficiency in the AC. The AC already has a noticeable impact on mileage.

Final question: this is the first time I've started a thread. I know there are numerous threads on grill blocks. Should I have looked one up and revived it instead of starting a new thread?

Any opinions (other than turn off the AC)?

[RedDevil]

I suspect your A/C radiator is behind the lower grill opening, so that might get better cooling instead of worse.
Blocking the upper grill means less air in total flows into the engine bay, so the under hood pressure is lower which helps the air flow through the lower grille.

You may want to monitor your air intake temperature though. If it draws air from behind the UGB, it will take air that is hotter than without UGB. That may benefit FE, but can also be detrimental if it causes pinging or if your engine also has an EGR.

I've got a cheap in/out digital thermometer sensor dangling in the intake opening of my Insight. It usually reads a few degrees above front bumper temp, but raises quickly in town. As it just got hot over here I've now removed most of my LGB.

[mcrews]

DO NOT TURN OFF THE A/C!!!

Really.
We all have levels we'll stoop to for better mileage.
I have ALWAYS left the digital a/c on in the Q45. And still achieved 30mpg on the road.

I will never delete a/c or ps.
But I do make a desission to drive slower.

[dwarfnebula]

That thing should be running hotter than that. The thermostat is most likely not closing, it should be up at least 190 without the grille block. I suppose the blocked grille could cause the fan to run more, I would guess that the extra drag may or may not be worth more than the aero gains depending on load and climate.

It's possible that blocking off airflow through the A/C condenser could raise high side pressures and therefor make the compressor harder to turn. If it gets to that point the A/C performance will suffer and it will not blow very cold.

[JeffD]

Thanks guys. The AC radiator is mounted pretty low and I'm still getting cold air, so I'm good so far. I just looked in my Haynes manual and it says the thermostat opens at 170 and is fully open at 194. I guess I'm technically ok until I hit the 190's and don't get cold air, but I still wonder about losing because of the fan. I can't seem to find what temperature the fan clutch is supposed to activate. The intake air is routed from the driver side fender (seems odd to me) but I'll keep an eye on the IA with the scangauge.

Maybe I'll run a tank without the grill block and see what happens. It seemed to help when the weather was cooler. Hard to compare with AC and changing weather conditions.

[redpoint5]

I don't think many here will think less of you for running AC. I'm a heat wimp, and set mine at 76. Much better than showing up at my destination soaking wet.

I had the same question about AC efficiency, so I'm glad you asked. There likely isn't a one-size fits all answer, but RedDevil's logic is sound. You're probably fine since your AC radiator is mounted low.

Not sure at what temp your fan clutch locks up, but on my car the E-fan kicks in at 212 degrees. I bet yours wouldn't fully engage until you were well into the 200s. My truck supposedly has a mechanical clutch, but it blows enormous amounts of air all the time. Perhaps it's those viscus forces you mention.

Originally Posted by dwarfnebula

It's possible that blocking off airflow through the A/C condenser could raise high side pressures and therefor make the compressor harder to turn.

The AC is a closed system and not subject to external pressure differences. Are you saying the high side pressure would rise due to a rise in condenser temperature?

[blowncopcar]

I too have a question regarding this but my fan is electric... My lower grille is blocked top and 65% on the bottom but I still run the a/c.... Is the aero gains not worth the extra power that the fan and also the condenser are taking? When I switch my a/c on I lose at least half my horsepower and no, I'm not kidding. Should I open the bottom grille more for better fe?

[user removed]

My Ranger has the grille totally blocked, but it also has openings below the bumper and a fairly large gap between the hood and grille without any insulation between the two.

Fan clutches usually run between 1500 and 2500 RPM depending on the temp of the air coming through the radiator. I seldom use the AC in the truck and have seen no rise in gauge readings.

You can actually hear the fan clutch when it is fully engaged, the fan noise will be significantly higher. In a lot of vehicles you will hear the fan running at higher speedds when you first start the car, then it starts to let the fan clutch "slip" more and fan noise is reduced.

The higher the coolant temperature (within reasonable limits) the better your mileage will be as long as you are not seeing a significant rise in coolant temperature. As long as you have a 50/50 mix of coolant the temps can get to 220 without any problem. In fact Mercedes bulletins stated that 256 degrees was not an issue with their diesels back in the 1980s but I would not like to see that temp level under any conditions, that was their maximum allowable. Not sure if it would apply to other cars.

When the fan clutch is worn out then you get problems. I used to show people their bad fan clutches by stopping the fan and spinning it backwards WHILE THE ENGINE WAS RUNNING! This was on the old Datsun-Nissan Z cars and there is NO WAY I WOULD RECOMMEND ANYONE TRYING THAT!

regards
Mech

[redpoint5]

Originally Posted by blowncopcar

I too have a question regarding this but my fan is electric... My lower grille is blocked top and 65% on the bottom but I still run the a/c.... Is the aero gains not worth the extra power that the fan and also the condenser are taking? When I switch my a/c on I lose at least half my horsepower and no, I'm not kidding. Should I open the bottom grille more for better fe?

I'm sure the correct answer varies from person to person. My car runs the cooling fan whenever the AC is in use, so I doubt heavy blocking affects performance much. If you see your engine coolant temps running much hotter than they are without the block, then too much blocking is being used. My car used to run 185 temps, and now run 190. Seems to be the perfect amount of blocking.

[dwarfnebula]

Originally Posted by redpoint5

The AC is a closed system and not subject to external pressure differences. Are you saying the high side pressure would rise due to a rise in condenser temperature?

Yup, high condenser temps cause high system pressures system-wide. Actually low side pressure and evaporator temp track each other linearly, with the old R-12 stuff it was straight over psi to degrees Fahrenheit, so 34psi would make for a 34 degree evaporator, 40 to 40 etc... Poor airflow, like a inoperative cooling fan or somesuch is a common cause of high system pressure and poor cooling.

As I said before if there's insufficient airflow through the condenser the A/C won't blow cold so you'll know it if it's a problem. The condenser has to shed all that heat it picked up in the evaporator somehow, the refrigerant can only carry so much heat.

And redpoint, your fan should not blow enormous amounts of air all the time. It's normal for it to blow a lot of air around for a little while after you turn it on, even cold, but it should loosen up until the motor gets good and hot. Get a new clutch on that baby, its worth some FE and the peace and quiet.

JeffD, I've been swinging wrenches for 10 years and I've never seen a temp rating for a fan clutch. If it runs all the time it's locked up, if it doesn't get stiff and move air when the engine's good and hot it's stuck loose. They're usually inexpensive enough that more scientific diagnostics are not cost effective.