Rationale for coolant system temps
Rationale for coolant system temps
(OP)
What exactly is the rationale for a particular coolant system temperature range?
Granted, most IC engines are designed to run at 190-210 deg F. But why? I can certainly understand the problems if you tried to run an engine at 400 deg F, but why not 250 deg F? On the other hand, why not set the system to run at 160 deg F?
I'm very aware that diesel engine manufacturers are quite concerned about engine temps, to the point of derating engines when the temperature reaches 220 deg F and starting an automatic shutdown sequence for a little bit higher temps.
But what happens if you run the engine at 240 deg F? Is it abnormal wear? Or is the engine at risk for seizing up?
I would appreciate some insight into this!!!
Granted, most IC engines are designed to run at 190-210 deg F. But why? I can certainly understand the problems if you tried to run an engine at 400 deg F, but why not 250 deg F? On the other hand, why not set the system to run at 160 deg F?
I'm very aware that diesel engine manufacturers are quite concerned about engine temps, to the point of derating engines when the temperature reaches 220 deg F and starting an automatic shutdown sequence for a little bit higher temps.
But what happens if you run the engine at 240 deg F? Is it abnormal wear? Or is the engine at risk for seizing up?
I would appreciate some insight into this!!!





RE: Rationale for coolant system temps
On the other hand, an engine that's too cool steals power from the combustion cycle.
TTFN
RE: Rationale for coolant system temps
Blacksmith
RE: Rationale for coolant system temps
During WWII, some of the piston aircraft engine manufacturers investigated using very high coolant temperatures. The idea was to increase the coolant temperature and thus allow a reduction in heat exchanger size.
I also read recently that the F1 engine guys had tried doing the same thing for the same reason. The FIA now has a maximum cooling system pressure rule, apparently for safety reasons.
Regards,
Terry
RE: Rationale for coolant system temps
RE: Rationale for coolant system temps
It is dangerous enough to remove the cap at 15 psi with water. Higher pressures are even more dangerous, and create more problems with hose life cost, water pump seals etc.
Hot oil is much more dangerous, and more expensive and a less efficient heat transfer medium.
Very hot oil or glycol also tends to rot hoses.
All these problems could be overcome, but at what cost for what gain.
The only gains are reduced radiator size, leading to improved aerodynamics, and improved thermal efficiency.
Another downside is increased under hood/bonnet temps, which can impact on volumetric efficiency and underbonnet component material choice and therefore costs for electrical insulation, hoses, belts, bottles, covers, manifolds, rockerboxes, etc.
Conversly, too cool decreases thermal efficiency and requires exceptionally large radiators.
The temperature has to be decided at design stage, as it effects many other decisions as indicated above, and also determines many clearances in the engine components.
Another limiting factor is that the engine must operate satisfactorily dureing it's warm up, so clearances wide enough to avoid seizing at the maximum temperature, still need to be tight enough to avoid excessive noise and damage at cold start
Regards
pat
RE: Rationale for coolant system temps
But there have been IC Recip engines made to run at very high temps. Some years back Cummins was experimenting with an Adiabatic engine.
RE: Rationale for coolant system temps
RE: Rationale for coolant system temps
Regards
pat
RE: Rationale for coolant system temps
Regards
pat
RE: Rationale for coolant system temps
I was told this was a bad idea because of engine oil. Apparently, the oil temp is substantially affected by the coolant temp (in several ways) and if it doesn't get hot enough, any condensate in the crankcase doesn't leave the oil. Water CAN get into oil, especially detergent oil, and can corrode all sorts of things...
Final rule: 180 degree stats instead of 210. Better at avoiding coking, etc. as previously discussed, and some reduction of the effect of high EGTs on things like oil sprayed on the undersides of the pistons to cool them. The decreased 'thermal efficiency' of the engine wasn't a major factor because exhaust temp was already too high, and that was limiting engine cycle efficiency...
RME
RE: Rationale for coolant system temps
On my Mini Cooper vintage race engine I shoot for ~220f max coolant (water and Red Line "Water Wetter") and ~240f oil temp. So far, so good!
I tried using 100% PG on my old Model A Ford a few years back and it seemed to work, it never boiled off, but coolant temps tended to go as high as 300f and I don't have an oil pump, much less an oil cooler. A note by the mfgr of the PG coolant is that it is NOT reccommended for a pressure system in 100% concentrations. I switched back to the same coolant as the race engines in the Ford before I melted the bearings or something else equally stupid!
Rod
RE: Rationale for coolant system temps
The different temperature ratings of different cars are likely based on the location of the sensor. I am sure they are all designed that given an average coolant mixture and the OEM system pressure that the coolant would be unlikely to reach over say 230*F at the cylinder wall.
There are waterless coolants that do not boil/vaporize even in a pressureless system. These have been successfully run in engines to 300*F coolant temps at the sensor - with no knock (i.e. no hotspots) and improved efficiency, especially on diesels.
Realistically if a theorectical coolant being used could still absorb heat at a sufficient rate at the cylinder wall this theorectical coolant could run at temps as high as 350*F.
It is the limitation of heat absorption if the coolant vaporizes at the cylinder wall that results in engines running coolant temperature below what would truly be ideal for the operation of the engine.
Ed.
RE: Rationale for coolant system temps