Temperature questions

[Falcon67]

My track engines I keep around 180.  If I'm going to run around on the street, 195~200.  Especially with an aluminum radiator.  Lots of benefits running hot - cleaner oil, less wear, better temp control and such. 

[My427stang]

Oil temps burn off water, not coolant temps, and of course that's obvious and not saying anyone doesn't know that already, but it makes it very difficult to compare one setup to another.

Ross, my experience has been that until the engine has been running for 15 minutes or so, the oil temp lags the water temp by a fair amount, maybe 20 degrees.  On my car with the clear valve covers, the condensation that may be present disappears about the time the coolant temperature hits 170, with the engine idling in the driveway.  The oil temperature is still lower than the coolant temperature, as read on the gauges, at that point.

My theory is that the hottest part of the engine is the combustion chamber, and the coolant is in direct contact with the opposite side of the chamber, so it picks up a lot of heat.  On the other side of the water jacket is the valvetrain area, so my guess is that the oil in that area is heated to about the same temperature as the coolant, despite what the oil temperature gauge (in the pan) may say.  Further, again despite what the coolant temperature gauge may say, the coolant in this area can be hotter than what is recorded on the gauge.  Seems like that heat could be radiated into the oil through the casting, and in a steady state condition that may be one reason why the oil temperature will go higher than the coolant temperature.

If you think about the circulation path of the coolant through the engine, coolant that goes all the way through the block to the back, up into the head, and then back forward to the intake will have the opportunity to pick up more heat than coolant that comes up through the block deck near the front of the engine, then into the head and the intake.  I'll be that if you could put a good temperature sensor at the rear of the cylinder head water jacket, it would read higher than one placed at the front of the head.

All this is just an explanation that makes sense to me, in light of the fact that the condensation all disappears while the engine is operating below water's boiling point (as read on the gauges).  Next time I start the car and idle it in the driveway, I'll have to try to observe where the condensation disappears first in the valve covers.  I'm betting it's going to be at the rear of the engine, because I think it's hotter back there.

Jay, No way to know I'd say, but I think it's likely due to where you are sensing the oil temp more than chamber heating through the water, metal and oil.  Common pan sensors are going to be a lot cooler than the oil until it saturates, and that's likely for a while.  In fact, I think on my way home today I will pull up the gauge display on my truck and watch when the water and oil temps converge and post here.  Dice warm day today so I'll time it.  Of course thats a Cummins not an FE, but gives me some fun as a brand new 52 year old retiree!    Regardless, as long as you are off-gassing, good to go, would like to see your results too.

[RustyCrankshaft]

Not a direct comparison, but I raced 6BT Cummins for a number of years and they tend to get #6 pretty toasty. So much so that I would knock the rear freeze plug and run a bypass to pull coolant out of the back of the block/head and send it back to the rad directly. I measured pressure and temps there and it was not uncommon to see 75 psi and 30-50* more temp at the back (these are averages from a 5.9 after a run and a shift RPM of around 6200).

Oil temp vs Coolant temp depends on even more factors. On my OBS 7.3 PowerStroke shop truck, the oil temp takes about 20 minutes longer to come up to temp and runs about 10* cooler than coolant temp unless its been pulling for a while. My Ranger with a 4.0SOHC and a temp sensor in the pan, the coolant temp and oil temp run within a few degrees of each other, but if you're just driving around it takes a while for the temps to meet, about 8-10 minutes.

Then you have the opposite, the Cat in my FLC, the oil temp NEVER warms up unless I hook something to it. I've driven it empty 140 miles in 75* ambient and never got the engine oil temp or trans temp over 100*. I think it's probably obvious in this case that it has a very large oil cooler and was meant to run WOT for hours/days at at time. Just for comparison that each engine and each build you have to take into consideration some of the specifics.

[Hipopinto]

Thanks guys

As I said I tend to worry way too much

I will restrict the oil to those rockers in short order

Dave

[cammerfe]

Put a pan of water on the stove at the lowest possible setting. The water will STILL disappear. It just takes longer than it will at full boil.

KS

[BigBlueIron]

Last summer in effort to see what things where doing I added an oil temp gauge on one of the supply lines to one of the 2 turbos on my current 390.  Fighting some flash boil overs with spirited "test passes". Oil temps would rocket to 250* in under 30 seconds. I didn't push it much past that, but I had several times before so undoubtedly the temps got much much higher. It would take 5 miles or better before oil temps settled back down closer to coolant temps.
With that I added a large oil cooler, -10 lines and 180* thermostat controlled sandwich adapter from Setrab, at the recommendation of some one here on the forum I would also recommend the brand, nice quality. That completely stabilized the oil temps and helped just a bit with the coolant temps when running it hard. I have sense removed the gauge laying my faith on the oil cooler.

Experience is the same as others with my 7.3, oil temps stay fairly low until your working it then they will be at or above coolant temp. Of course they have a factory water to oil cooler to help.