Well here goes ! This week i put 64 miles on "Rhonda" with 7 oil temp. senders wired to a rotary switch to one gauge. This was done to reduce the cost of the test and to be able to scroll thru the different senders at will and log temps. at various places on my engine. I can tell you now that I am surprised at my findings and that some of my preconceived findings were totally wrong.
Let me set some parameters of my test. I have a 2110cc, dual Weber carb. engine that dyno. tested at 140hp. Built by me. I have a new 36hp doghouse fan shroud with a std. 5 row internal oil cooler, no thermostat, no flaps, no sled tins. I have 1 5/8" heater boxes, 1 5/8" A-1 exhaust system. My carb. jets are 120 mains, .49 idle, 220 A/C s and F-11 emulsion tubes. My Plugs read coco brown and my exhaust is dark grey. My "Fast" air fuel ratio meter reads 13.8 to 1 and I get 23 mpg (if i don't have my foot in it. which is hard to do yet)
My gauges in the car are Dakota Digital CHT and Oil Temp. Both are accurate to within 2 to 3 degrees.I tested them on my stove with a pot of boiling water and a battery to 212 degrees F. I tested (and numbered) all 7 oil temp. senders. They are all within + or -3 degrees of 212.
Any morning I can walk out and look at a thermometer hanging on my garage in the shade an get a reading of what the current temperature is around my neighborhood. i use this as a standard when I initially turn on my ignition switch and read what the two Dakota gauges say. The Dakota Gauges are consistently indicating 3 degrees lower (with error corrections to the boiling water data for each sensor). Using the rotary switch while the engine is cold I can scroll thru each sensor and make the corrections. What I have done on the data submitted here is just average out those temps to make it easier to follow and there isn't that much variation anyway. The data below is what I have consistently recorded and averaged on 5 road tests in unusually hot weather even for out here in So Cal.
Average ambient air temp: 93 F. Average cold engine temp at gauges before start-up: CHT 89 F. Oil temp. 90 F.
Cylinder head temps. at time of data logging
Oil temp sender locations Street CHT: 337 Freeway CHT: 333 5 min. Idle CHT: 330
Thin Line Sump 152 F. 157 F. 170 F.
Rear oil pressure relief valve 175 F. 182 F. 170 F.
Type 3 dip stick block-off plate 188 F. 189 F. 185 F.
External oil cooler in 180 F. 192 F. 174 F.
External oil cooler out 173 F. 187 F. 163 F.
Dog house oil cooler in 163 172 F. 150 F.
Dog house oil cooler out 162 F. 171 F. 151 F.
Notes about what the above data tell me:
1. The doghouse cooler isn't reducing the oil temp. that much at any speed. This was a big surprise for me.
2. The external oil cooler does a better job of cooling the oil
3. The oil temp gets reduced more up by traveling thru the hoses and crankcase from the external cooler to the doghouse cooler.
4. The Thin Line sump is the worst place to monitor oil temps. I believe that cool air flow over the surface of this sump gives faulty readings but does contribute to cooling the oil in the sump.
5. The rear pressure relief valve give accurate readings but because the oil has to slowly reach around the plunger to give the sensor a change in temp. it is always lagging in giving an accurate and timely reading. I noticed that sometimes it was lagging as much as 15 degrees.
6. The Type 3 dip stick block-off plate allows it's sender to have excellent access to the oil temp in the crank case. It gave more accurate and faster change readings than the External oil cooler inlet readings which had a chance to cool somewhat thru the oil filter before reaching the oil sender just in front of the External oil cooler.
7. The External oil cooler does a better job of cooling the oil than the stock oil cooler. (Mine is located in the left rear fenderwell) The temp sender on the inlet side would be my next choice of placement as it is receiving the oil directly from the pump and sump. It reacts to changes in oil temp rapidly.
8. When I think about how that gallon or so of oil circulates thru the engine in seconds and that the stock oil cooler is like a thick core radiator with only about 20% of the fans air directed to it, I can see why it doesn't have a chance to cool the oil very much. Plus some of the oil is bypassed by the front relief valve.
9. I did not choose to put a sender in the bung for the oil pressure sending unit. I think it is a poor place to do so because it would practically have no contact with any oil flow and at best would give you crankcase metal temperature only. I know that a lot of people put them there but i just think that there are better places on the engine to install one. As a mater of fact, there is a stock plug about 2 inches from the oil pressure port and on top of the crankcase that would be a much better alternative. But it could only be installed when you have the crankcase apart to prevent metal shavings from getting into the oil galley and to insure you don't insert it to far into the oil galley to impair oil flow.
That's if folks. The following are photos of just where I installed the senders on the engine.........Bruce
