Bottom rad hoses get old, soft, and collapse when the water velocity rises, cuting off flow and overheating the engine. Warm the engine and rev the throttle while watching that hose. Some hoses had a wire coil in them to prevent this. Dan
circulation,
Stands up in the lab and in reality. Water takes a certain amount of time to achieve thermal transfer. Just physics and thermodynamics. Fluid dynamics through the engine determines the coolant temperature, water speed and flow asymmetries play a critical role in keeping hot spots in the engine to a minimum. You want to see cavitation cut open a cylinder head and take a look at how the passages are cast.
They don't turn to steam because the flow is too high, though. That is the fallacy.
Sorry. I don't buy this explanation in its entirity.
What you have described above is a batch process, and that is not what is happening in these systems, IMHO.
If you lose surface area due to degassing (I doubt it is truly cavitation, but leave that open to possibility) then you will lose some transfer rate. On that, we agree.
Hooey. When the water is flowing slowly, it its temperature does decrease more in the radiator, but you're putting fewer gallons/minute of cool water into the engine. When it flows fast, the temperature may only drop a little bit, but you're pumping a much larger VOLUME of water through the engine, so the total amount of HEAT transferred to the radiator is the same. The engine is actually better off with the water flowing fast and undergoing less temperature drop in the radiator, because that leads to a more uniform temperature throughout the engine. Up to the point that the engine block can't support the fast flow and irregular flow pockets develop, that is.
Bullshit then, bullshit now.
This is not science. This is urban legend.
Well Ryan, could you possibly explain why, when I removed a 160* thermostat and replaced it with a 195* themostat, my car stopped overheating?? Doesn't make sense, does it...
SteveL
| coolant never heats up to normal temperature. | a stuck open or missing thermostat is bad in the long run because it | will sludge your oil by not allowing the engine to reach temperature where | moisture is evaporated from the crankcase. It will also take forever to get | hot air out of your heater.
True only in a cold climate. Here where lowest temperature @ dawn is
24°C, my Mitsubishi 4G15P engine has a carburetor & no auto-choke / thermostat : engine takes longer to heat up, less heat reaches battery terminals. In 28°C air, cylinder head can reach 40°C ( ideal temperature per
These accounts have been reported and I don't doubt them, in most cases. While the effect may well exist in some engines, the reasoning that water has to cool over time as a static batch process is flawed. Right observation but totally wrong interpretation.
The 160-degree stat was a dud.
Nope, after testing the 195* stat and installing it, I tested the
160* stat, it started to open at 150* and was fully open at 165*, and the car was overheating, as in 240*, after climbing the Snoqualmie Pass...The very next weekend, back over the pass, and never got above 195*...
SteveL
I still don't understand why this would be so. Yes, if the water is flowing faster, less heat will be transferred to and from any particular molecule of water. But that same molecule will circulate many more times through the system due to the higher flow rate, giving it more chances to pick up that smaller amount of heat.
Your 160 was stuck closed? :)
solution: i replaced the thermostat and the engine runs much cooler, and steady temp! so low and behold, the thermostat MUST have been bad!
thanks to everybody for their help and entertainment! hehe.
bob
Thanks for the update. It is nice to hear what worked or didn't!
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT'sbob wrote:
Sometimes my Volkswagen Golf 1300 cc from 1985 ran hot while the Liquified Petrol Gas evaporator froze, causing the car to stop. The cause was air in the cooling system, making it difficult for the cooling liquid to flow (no communicating storages?). When I refilled the system while running the engine and opening and flushing the heater, the problem was gone. Only for a while because in my case the real cause was a small leak. Maybe some of this occurred in your situation too?
shakiro
Absolute nonsense...
Professor
Absolute nonsense...
Professor
It's not so much about temperature as about heat removal. If the water flows slower, the radiator gets hotter, so the heat flow from water, through the radiator wall and to the air will increase. This means that _on average_ (average of engine in- and outlet water) the temperature of the engine will be lower. OTOH, the temperature gradient inside the engine (between in- and outlet) could become so high that somewhere inbetween the allowed temperature will be exceeded, leading to damage in the engine. OTOOH, if there is a transient from laminar flow to turbulent flow, the heat transfer coefficients, inside the engine between water and cilinder lining, and inside the radiator between water and radiator wall, could suddenly become a lot higher, leading to a better heat removal inside the engine as well as inside the radiator. Normally the transient from laminar to turbulent flow occurs at some flow increase.
shakiro - loves to complicate things
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.