Engine speed and Temperature

Moderators: Amskeptic, Sluggo

Post Reply
User avatar
JLT
Old School!
Location: Sacramento CA
Status: Offline

Engine speed and Temperature

Post by JLT » Mon Sep 26, 2016 5:31 pm

I got a good demonstration yesterday about the relationship between engine speed and engine temperature yesterday.

I was tooling along a flat stretch if Interstate 5 in what was probably 95-100 degree heat. I have one of those VDO oil temp gauges where the sensor takes the place of the drain nut. (I don't know if the readings I get are the actual temperature of the oil, but I assume that they are proportional.) The readings are normally between 120 and 180.

When driving at 65 mph with my stock 1600 engine, I was getting readings of 205 or so. When I slowed down to 60, the temp dropped to about 180.

I'd always assumed that the faster the engine spun, the more air was going through the engine's cooling system. I guess that's still true, but there seems to be a point where that increase is outbalanced by the greater heat produced by the engine itself. So I guess I'm going to keep my cruising to about 60 (at least in hot weather), since that seems to be the sweet spot for the engine's cooling system.
-- JLT
Sacramento CA

Present bus: '71 Dormobile Westie "George"
(sometimes towing a '65 Allstate single-wheel trailer)
Former buses: '61 17-window Deluxe "Pink Bus"
'70 Frankenwestie "Blunder Bus"
'71 Frankenwestie "Thunder Bus"

User avatar
asiab3
IAC Addict!
Location: San Diego, CA
Contact:
Status: Offline

Re: Engine speed and Temperature

Post by asiab3 » Mon Sep 26, 2016 7:05 pm

I've noticed the exact trends you're seeing on T1 and T4 engines. Something I also notice is tons of people talking about "engine temp" or "oil temp" and not mentioning where they're measuring, and under what conditions.

From what I gather before I stopped checking, high speeds on a Type 1 do fantastic things for the cylinder head temperature, but those same high speeds did give me higher oil temperatures. But the numbers we measure are drastically different depending on where you measure. So I don't give a rat's ass about 210+ at 68mph on a hot summer day, because the oil coming off the piston skirts can be 50* hotter and the oil hitting the bearings can be 50* cooler.

So drive it and smell it and check the dipstick. The oil will let you know if it's burnt. The oil will let you know if it is disappearing.

Robbie
1969 bus, "Buddy."
119k miles with me.
296k miles on Earth.

User avatar
Bleyseng
IAC Addict!
Location: Seattle again
Contact:
Status: Offline

Re: Engine speed and Temperature

Post by Bleyseng » Mon Sep 26, 2016 8:51 pm

That's why you place the oil sensor in the sump to check the temp on the majority of the oil for a average. Yes, of course the oil will be cooler coming out of the cooler as it goes to the bearings, it's been cooled but you are looking at what the temp of the bulk of the oil is.
By the time you smell the oil being burnt. the engine has run too hot.
Geoff
77 Sage Green Westy- CS 2.0L-160,000 miles
70 Ghia vert, black, stock 1600SP,- 139,000 miles,
76 914 2.1L-Nepal Orange- 160,000+ miles
http://bleysengaway.blogspot.com/

Post Reply