Originally Posted by serialk11r
Intuitively this is right, the heat rejection rate doesn't go down that much after it's warm anyways since the flame temperature and exhaust temperature are much, much higher than coolant temperature.
But what about lubrication? My engine makes groaning sounds when it's cold that go away when the oil warms up...very disconcerting :/ Wasting a bit of gas at low load letting the engine warm up faster makes me feel better about my bearings. Maybe I just need a 5W-20 instead of a 10W-30.
My Ranger made horrific noises until I looked at it carefully and found the exhaust heat shield had cracks near the connecting clips. Found it by banging the exhaust system with my hand. Ripped off the heat shield and it sounds just about like a new vehicle.
Not sure what a "groaning noise" would actually sound like but mine was induced by certain periods of resonance that was much more prominent at certain RPM. This is a 15 year old factory exhaust. I think it is stainless steel and I can find no reason to replace it with the noise problem cured.
The exhaust manifold heat shield would be my best guess as the cause of your noise, but any guess is just that, a guess. Based on a lot of experience the guess becomes somewhat educated.
As far as cold oil pressure, that is not a concern, at least to me, after seeing my (long gone) 1937 Ford that produced 60 PSI of oil pressure cranking at 100 RPM on the original 6 volt system and starter motor. You have plenty of oil pressue in a cold engine at any RPM above 100 which you will never see in any modern engine, even cranking. After the first second of turning the key to the crank position, on initial start, you have plenty of oil pressure.