racetech
Enthusiast
As a new Viper owner, I thought I'd try to share some information that I have on cooling systems. I haven't had the chance yet to "play" with my 2000 RT/10 yet, but I have some general tips based on a lot of data.
As far as "the" optimal engine operating engine temperature, there are variables--but it's remarkable how often a naturally-aspirated gasoline engine shows significant horsepower losses on the dyno (crankshaft HP) either above or well below 170°F mean coolant temperature. The problem as I see it is keeping it close to that temperature under varying operating conditions.
Under full-load, heat builds up rapidly in the cylinder heads and the coolant is not heated uniformly. Cylinder temperatures rise fast under power and the coolant gets particularly hot (often exceeding the presurized BP) as it flows over the combustion chambers and around the exhaust ports.
What you see on your temp gauge does not have direct correlation with what the cylinders "see" under WOT (wide open throttle). A temperature gradient is formed within the cylinder head water jackets. The gauge only reads a mean coolant temperature as it is some distance from the chambers and in a place where coolant from different regions of varying temperatures mix together.
Also, having personally tested a number of thermostats, the true opening temperature can vary by as much as 10°F from the number stamped on them! (depending on the manufacturer)
The true cylinder temperatures will be influenced by a number of factors including the fuel mixture (the richer, the cooler), spark timing (******** timing causes high exhaust temps and puts heat into the cylinder heads), the rate at which your engine produces heat (more hp = more heat), the amount of on-throttle time, and the ability of the radiator/fan/airflow to dissipate heat.
In a drag race, a Viper makes it through the quarter mile so quickly *smile* that there are only a couple of liquid transfers between the engine & radiator--only about 1 or 2 cycles. The radiator doesn't really get a lot of time to dump heat in this circumstance.
Endurance engine operation of a car is an entirely different matter. Road race or circle track cars really need a radiator that can at least keep up with the rate at which heat is produced. Street driving can be tough because the car may not be getting much "clean" air into the radiator and the air conditioning condensor adds a lot of extra heat. The ambient outside air temperature and humiditiy also affect heat dissipation rates.
Bottom line? A 180°F thermostat is not a bad idea, but don't expect to feel a substantial performance improvement. No thermostat can do a thing about the rate at which the car's cooling system can dissipate heat. I think I'll put one in myself. A 180°F mean coolant temp won't screw up the computer parameters (don't use the 165°F thermostat and NEVER eliminate the thermostat entirely). Watch the gauge--if it keeps rising as you're running your car, you may need "more" radiator and/or cooling fan. I start to get nervous when it exceeds 210°.
As far as running an electric radiator fan after the car is turned off, this is not done for the reasons most people think. It will not cool the engine significantly because there is no coolant flow once you shut off the engine (the water pump stops). Mostly, it helps control "afterboil" problems (coolant loss into the overflow reservoir at engine shut down).
Do not use a lower pressure radiator cap. Every pound of pressure exerted on coolant raises the boiling point 3°F. A low-pressure cap will allow steam pockets to develop where the coolant is in contact with hot spots. Never run straight antifreeze (ethylene glycol)--it can only carry about 60% of the heat of plain water and actually has a higher freezing point at concentrations either above or below 60/40 ethylene glycol/water. Hope this info is of use to someone!
As far as "the" optimal engine operating engine temperature, there are variables--but it's remarkable how often a naturally-aspirated gasoline engine shows significant horsepower losses on the dyno (crankshaft HP) either above or well below 170°F mean coolant temperature. The problem as I see it is keeping it close to that temperature under varying operating conditions.
Under full-load, heat builds up rapidly in the cylinder heads and the coolant is not heated uniformly. Cylinder temperatures rise fast under power and the coolant gets particularly hot (often exceeding the presurized BP) as it flows over the combustion chambers and around the exhaust ports.
What you see on your temp gauge does not have direct correlation with what the cylinders "see" under WOT (wide open throttle). A temperature gradient is formed within the cylinder head water jackets. The gauge only reads a mean coolant temperature as it is some distance from the chambers and in a place where coolant from different regions of varying temperatures mix together.
Also, having personally tested a number of thermostats, the true opening temperature can vary by as much as 10°F from the number stamped on them! (depending on the manufacturer)
The true cylinder temperatures will be influenced by a number of factors including the fuel mixture (the richer, the cooler), spark timing (******** timing causes high exhaust temps and puts heat into the cylinder heads), the rate at which your engine produces heat (more hp = more heat), the amount of on-throttle time, and the ability of the radiator/fan/airflow to dissipate heat.
In a drag race, a Viper makes it through the quarter mile so quickly *smile* that there are only a couple of liquid transfers between the engine & radiator--only about 1 or 2 cycles. The radiator doesn't really get a lot of time to dump heat in this circumstance.
Endurance engine operation of a car is an entirely different matter. Road race or circle track cars really need a radiator that can at least keep up with the rate at which heat is produced. Street driving can be tough because the car may not be getting much "clean" air into the radiator and the air conditioning condensor adds a lot of extra heat. The ambient outside air temperature and humiditiy also affect heat dissipation rates.
Bottom line? A 180°F thermostat is not a bad idea, but don't expect to feel a substantial performance improvement. No thermostat can do a thing about the rate at which the car's cooling system can dissipate heat. I think I'll put one in myself. A 180°F mean coolant temp won't screw up the computer parameters (don't use the 165°F thermostat and NEVER eliminate the thermostat entirely). Watch the gauge--if it keeps rising as you're running your car, you may need "more" radiator and/or cooling fan. I start to get nervous when it exceeds 210°.
As far as running an electric radiator fan after the car is turned off, this is not done for the reasons most people think. It will not cool the engine significantly because there is no coolant flow once you shut off the engine (the water pump stops). Mostly, it helps control "afterboil" problems (coolant loss into the overflow reservoir at engine shut down).
Do not use a lower pressure radiator cap. Every pound of pressure exerted on coolant raises the boiling point 3°F. A low-pressure cap will allow steam pockets to develop where the coolant is in contact with hot spots. Never run straight antifreeze (ethylene glycol)--it can only carry about 60% of the heat of plain water and actually has a higher freezing point at concentrations either above or below 60/40 ethylene glycol/water. Hope this info is of use to someone!
