Another fan question
Thread Starter
Racer
Joined: Sep 2012
Posts: 252
Likes: 18
From: Austin TX
Another fan question
Hey everyone. Have a question about the rad fan on my 86. I've tried a search but can't find the answer to my question. I have the dual fan option and I just replaced the thermo with a 180deg. The temp stays right around 180. The fan comes on at that temp too. I thought it wasn't supposed to come on till like 211? It appears to have the stock chip installed. Could something else be causing the fan to come on that early?
Scott
Scott
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
The rear fan is controlled by the ECM. It uses the CTS (Coolant Temperature Sensor) on the front of the intake manifold under the throttle body to determine when to turn on the fan. According to the BUA firmware in my '86, it turns on the fan at 107.8°C = 226°F.
The ECM will also turn on the fan if the AC is turned on. It uses an input from a switch in the AC high pressure line for this.
The auxiliary fan in front of the AC condenser is controlled by a thermal switch in the driver's side head between spark plugs #1 and #3. It turns on the fan at 238°F.
The ECM will also turn on the fan if the AC is turned on. It uses an input from a switch in the AC high pressure line for this.
The auxiliary fan in front of the AC condenser is controlled by a thermal switch in the driver's side head between spark plugs #1 and #3. It turns on the fan at 238°F.
Thread Starter
Racer
Joined: Sep 2012
Posts: 252
Likes: 18
From: Austin TX
Then maybe it does have an aftermarket chip. I was expecting to see a name brand on it, like hypertech or something. Is the transmission shift points changed by the ecm also? The car shifts quick and hard, definitely not stock.
Safety Car
Joined: Jan 2004
Posts: 3,556
Likes: 13
No
Nothing to say a previous owner has not rewired the fans and installed a aftermarket lower temp fan switch
so the fan run at a different temp to stock setting independent of ECM control
Only way to find out would be to follow the fan wiring and see where it actually goes .......
Do both fans run at the same time / temp? A sure sign it is no longer stock
Way back in the good ole days , guys put custom tunes (with diff fan temps , etc ) on the stock memcals ( chip )
Nothing to say a previous owner has not rewired the fans and installed a aftermarket lower temp fan switch
so the fan run at a different temp to stock setting independent of ECM control
Only way to find out would be to follow the fan wiring and see where it actually goes .......
Do both fans run at the same time / temp? A sure sign it is no longer stock
Way back in the good ole days , guys put custom tunes (with diff fan temps , etc ) on the stock memcals ( chip )
Last edited by vetteoz; Oct 29, 2012 at 02:19 AM.
Thread Starter
Racer
Joined: Sep 2012
Posts: 252
Likes: 18
From: Austin TX
[QUOTE=vetteoz;1582195980]
Do both fans run at the same time / temp? A sure sign it is no longer stock
That im not sure of, I just went by the sound. I'll check it out though.
I believe it was used to Autocross because the rear camber on both wheels were -2.8deg. So the modified shifting makes sense and who knows what else was done to it.
Do both fans run at the same time / temp? A sure sign it is no longer stock
That im not sure of, I just went by the sound. I'll check it out though.
I believe it was used to Autocross because the rear camber on both wheels were -2.8deg. So the modified shifting makes sense and who knows what else was done to it.
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
Your shifting could be from a "shift kit" installed in the trans valve body, OR it may just be simple TV cable adjustment. Pulling too much tension on the TV cable will stretch out each gear and cause a harder upshift. More noticable driving in 3rd gear/auto.
Not good for anything IMO except wear on the drivetrain.
A "soft" or slack TV setting will get early upshift and early OD engagement, also not good when it causes the engine to load down when its not generating sufficient power to pull the taller gear. Rule of thumb to test the TV cable...OD upshift should take place at 55 mph if you start out in OD. Not less. The TCC also gets involved by locking up the converter to create a non-slip upshift when driven in 3rd gear. City driving in 4th bypasses the TCC lock-up and allows for the softer upshift. TCC also allows engine braking and a "positive" drive until it slows to 1100 rpm or when the brake is touched. TCC drops out the instant you tap the brake so it does not stall the engine at low rpm engagement.
On the fans and T-stat, remember the stat only controls the min coolant temp. That a 180 stat opens at 180 and allows the coolant to circulate to collect heat and drop it off in the radiator. IF the hot water flows thru the rad when there is little or no air flow, say at a stop light when you;re around 190...it will continue to rise even though the water is circulating. Its a 2 part process... the water must be circulating AND there must be air flow (from driving or the fan) to remove heat from the water as it travels thru the system. Maintaining a stable temp is more desirable than having a system that spikes from 160 to 200 as fans and stats open/close. Thats how you get weakened head gaskets IMO...by letting the temps spike and flirt with the different metals expansion rates. there is nothing to be concerned about until you see 240 on the gauge...then you get to worry.
This is a good place to mention cleaning under the radiator shroud. This is a normal maint item that MUST be done whenever higher than normal temps appear. The vette nose sucks up trash like a vac cleaner and directs it thru ducts to get trapped between the radiator and the condensor. There is NO WAY to see it or reach it or flush it with water...until you pull the top shroud off and reach in. Its not as bad as it sounds... and cleaning annually will keep the rad from getting its veins/fins filled with dirt and debris.
Watch the area on the front side of the condensor as well...thats the first stop for trash collection. If it gets past there, its trapped in the rad area where it WILL block most of the air flow and cause high temps.
Sounds like yours was set up to be stable with a similar stat and fan.. A level temp range. Get yourself a FSM and review the electrical section and the great color wiring diagrams to try and see what the PO did as far as electrical engineering.
A quick but very important tip: the electrical on a corvette is all about the grounds...ground path is how everything is managed and operated, NOT power wires. Everything is HOT most all the time. Things get turned on/off by the ground. Thats usually how someone tricks the fan into running sooner or all the time or manually.
Having the fans on about the same time as the stat opens should try to keep a stable temp since both water and air are moving. A fan that comes on before the stat opens is not cooling the heated water since that hot water is trapped in the block...not in the radiator where the fan is working. Pointless. The stock stat is 190 IIRC and the stock main fan is 226 as Cliff stated. These cars depend on motion for most of the cooling. The a/c triggers the main fan to draw air in thru the air handling system so the extreme condensor heat can be pulled out, just as the radiator works. That air can and does get pulled into the radiator, so the a/c does not always help. It can hurt your op temps when the a/c heat adds to the radiator heat and causes the eng temps to rise. Even though the fan is running its adding condensor heat to the already heated radiator. More added heat, same amount of airflow....eng temp rises. Only a problem in the extreme climates...Az, dessert towns and the extreme summers.
The only downside to the fan being on too soon would be the longivity of the fan motor. It'll run pretty much all the time if you allow it to come on at 160-180..depending on the climate. That will also make it hard to warm up in the winter. Mine is set to provide max cooling in summer, so today when it was 35 degrees it refused to even get to the stat temp of 180....too much air flow when driving and too much heat exchange. Mines a safety stat that allows some water to always pass no matter the temp. In winter it needs a plain 190 back so I can create more heat. No need to see my breath freeze and hit the floor while driving...
The engine needs to be near 180-200 to run efficiently (based on the tune) and to heat the oil enough to lubricate properly and boil off moisture in the oil from condensation...hot/cold cycles. And if you want a heater...its got to be at least 160 to keep feet warm.
Not good for anything IMO except wear on the drivetrain.
A "soft" or slack TV setting will get early upshift and early OD engagement, also not good when it causes the engine to load down when its not generating sufficient power to pull the taller gear. Rule of thumb to test the TV cable...OD upshift should take place at 55 mph if you start out in OD. Not less. The TCC also gets involved by locking up the converter to create a non-slip upshift when driven in 3rd gear. City driving in 4th bypasses the TCC lock-up and allows for the softer upshift. TCC also allows engine braking and a "positive" drive until it slows to 1100 rpm or when the brake is touched. TCC drops out the instant you tap the brake so it does not stall the engine at low rpm engagement.
On the fans and T-stat, remember the stat only controls the min coolant temp. That a 180 stat opens at 180 and allows the coolant to circulate to collect heat and drop it off in the radiator. IF the hot water flows thru the rad when there is little or no air flow, say at a stop light when you;re around 190...it will continue to rise even though the water is circulating. Its a 2 part process... the water must be circulating AND there must be air flow (from driving or the fan) to remove heat from the water as it travels thru the system. Maintaining a stable temp is more desirable than having a system that spikes from 160 to 200 as fans and stats open/close. Thats how you get weakened head gaskets IMO...by letting the temps spike and flirt with the different metals expansion rates. there is nothing to be concerned about until you see 240 on the gauge...then you get to worry.
This is a good place to mention cleaning under the radiator shroud. This is a normal maint item that MUST be done whenever higher than normal temps appear. The vette nose sucks up trash like a vac cleaner and directs it thru ducts to get trapped between the radiator and the condensor. There is NO WAY to see it or reach it or flush it with water...until you pull the top shroud off and reach in. Its not as bad as it sounds... and cleaning annually will keep the rad from getting its veins/fins filled with dirt and debris.
Watch the area on the front side of the condensor as well...thats the first stop for trash collection. If it gets past there, its trapped in the rad area where it WILL block most of the air flow and cause high temps.
Sounds like yours was set up to be stable with a similar stat and fan.. A level temp range. Get yourself a FSM and review the electrical section and the great color wiring diagrams to try and see what the PO did as far as electrical engineering.
A quick but very important tip: the electrical on a corvette is all about the grounds...ground path is how everything is managed and operated, NOT power wires. Everything is HOT most all the time. Things get turned on/off by the ground. Thats usually how someone tricks the fan into running sooner or all the time or manually.
Having the fans on about the same time as the stat opens should try to keep a stable temp since both water and air are moving. A fan that comes on before the stat opens is not cooling the heated water since that hot water is trapped in the block...not in the radiator where the fan is working. Pointless. The stock stat is 190 IIRC and the stock main fan is 226 as Cliff stated. These cars depend on motion for most of the cooling. The a/c triggers the main fan to draw air in thru the air handling system so the extreme condensor heat can be pulled out, just as the radiator works. That air can and does get pulled into the radiator, so the a/c does not always help. It can hurt your op temps when the a/c heat adds to the radiator heat and causes the eng temps to rise. Even though the fan is running its adding condensor heat to the already heated radiator. More added heat, same amount of airflow....eng temp rises. Only a problem in the extreme climates...Az, dessert towns and the extreme summers.
The only downside to the fan being on too soon would be the longivity of the fan motor. It'll run pretty much all the time if you allow it to come on at 160-180..depending on the climate. That will also make it hard to warm up in the winter. Mine is set to provide max cooling in summer, so today when it was 35 degrees it refused to even get to the stat temp of 180....too much air flow when driving and too much heat exchange. Mines a safety stat that allows some water to always pass no matter the temp. In winter it needs a plain 190 back so I can create more heat. No need to see my breath freeze and hit the floor while driving...
The engine needs to be near 180-200 to run efficiently (based on the tune) and to heat the oil enough to lubricate properly and boil off moisture in the oil from condensation...hot/cold cycles. And if you want a heater...its got to be at least 160 to keep feet warm.
Last edited by leesvet; Oct 29, 2012 at 05:01 PM.
