Help Me Understand Engine Temps - IR Thermometer

mca · 07-19-2009, 03:54 PM

Last week I installed a numbered oil temp overlay (http://newvintageusa.com/911modules) so that I could better keep track of my engine temps.

Summer here in Charleston is pretty hot. The humidity makes it unbearable at times. Now that I have a numbered gauge I can see that I am running at 210. But after moving through some stop and go traffic I get a little higher - 215 or 220. Highway driving always stays at 210 (takes a while to get there). Before the summer hit I had a hard time getting up to 200.

Today I picked up an IR thermometer just to confirm the gauge readings. After all, my car is an 82 but the engine is a rebuilt 80. I believe they use the same temp sending unit - I "think" I cross checked the part #s when I pulled the 82 engine out of my car.

Anyhoooo. With my gauge showing roughly 215 I got the following readings using the IR gun:

Oil supply line = 197 degrees
Oil return line = 185 degrees
Oil filter = 215 degrees
Oil tank = 190 degrees
Sump = 195 degrees (although it was hard to get a good shot here)

The only thing that matched my gauge was the filter. Am I hitting the right spots?

I think my temps are good for this time of year. But I am considering adding a fan to my fender mounted cooler just to keep the temps down all summer long. I have the elephant finned lines and cooler (no fan).

ShakinJoe · 07-19-2009, 04:06 PM

You have to be careful with IR guns as they are all so very different. First, the little red laser dot IS NOT the spot you are measuring, but more the "general" area. let me explain. Consider an IR gun to be just like a flashlight that you point at a wall. You do not get a spot on the wall, but a big area of light. The IR works ion the same manner, but they use "spot-ratios" to tell how big the spot is. As an example, a 2:1 will read a 1 inch square area when the gun 2 inches away. the further away you are, the less accurate it gets.

In addition to this, you must be careful not to measure reflective items unless you change the emissivity factor of the instrument. The best thing to measure is a tire as it is dull and black.

Hope that helps.

TimT · 07:43 PM

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burgermeister · burgermeister's Garage

Quote:

Originally Posted by TimT

The Oil filter is the first stop the oil makes as it leaves engine..If you see 215 at the filter, and 215 at the gauge.. I'd venture that your gauge is reading accurately..

I thought the external thermostat, the front cooler, and then the oil filter, were the first stops, in that order.

TimT · 07:37 PM

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mca · 07-19-2009, 05:06 PM

Quote:

Originally Posted by ShakinJoe

Hope that helps.

Sure does. I was probably within 6 inches for each measurement - except the sump plate.

86 911 Targa · 07-19-2009, 05:09 PM

mca,

Please check my posts RE: Engine oil temps ect...

Good luck,

Gerry

mca · 07-19-2009, 05:10 PM

Quote:

Originally Posted by TimT

The Oil filter is the first stop the oil makes as it leaves engine..If you see 215 at the filter, and 215 at the gauge.. I'd venture that your gauge is reading accurately..

The temps on the surfaces of the oil lines are relative... They will be less than the temps of the oil as it leaves the engine.. (check oil filter)

oil temps at 215-220 are not bad... helps the condensates perc out of the oil...

Quit worrying, drive the car... Also a fan would never be a bad idea

Thanks. I am not worried. BUT I'd like to be able to keep the engine cool in the event that I get in some traffic. I hesitate to drive up to VA during the summer due to the construction on 95. I can't imagine sitting on the highway at a dead stop in 100 degree heat without a fan.

Would you say the my cooler is doing a decent job of lowering oil temps by 12 degrees?

JMH82SC · 07-19-2009, 05:26 PM

Quote:

Originally Posted by TimT

scavenge pump>filter..

thermostat opens and closed sending oil to the cooler...

Oil is filtered first....

This statement is misleading. Oil is not filtered first. The return line of my 82SC oil tank goes to the filter. If the external thermostat is closed oil is bypassed around the front cooler and filtered on the way back to tank. If the thermostat is open oil is diverted to front cooler and filtered once cooled on the way back to tank.

uwanna · 07-19-2009, 05:35 PM

MCA,
I did the same testing you did with an IR thermo. Got roughly the same results.
Run the car till guage reached 210, jumped out, and at idle got these readings:
frt cooler input 200, frt cooler output 185, oil tank 210, filter 210.
Its a mystery to me why the tank and filter read 210, but the incoming oil to the tank was 185deg. DUH! But thats the facts Jack.
By the way, the oil flow goes to the ext thermostat first, them to the cooler if it is open and return to the filter. Ego if the ext thermostat is closed, it goes directly to the filter. See below

Jascha · 07-19-2009, 05:41 PM

Here are the paths that the oil takes: (the filter is a great spot to check the 'first' external point in the oil circuit).

Note IR meters respond differently depending on the surface / color being interrogated...some allow for a correction factor to be entered.

mca · 07-19-2009, 05:55 PM

great diagram. thanks for posting.

uwanna ... i wonder the same thing ... why isn't the oil in the tank the same temp as the return line temp? Could it be radiant heat from the engine?

TimT · 07:37 PM

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Jascha · 06:11 PM

The important thing to remember is that IR Thermometers respond selectively to the measured surface.

For example, the 'emissivity' of aluminum (oxidized) is 0.2-0.4 compared to iron of 0.5-0.9 and steel (polished) is only 0.1

The simple and inexpensive meters don't allow you to set this factor so you might get contradictory readings depending on what you pointing at...

uwanna · 07-19-2009, 06:10 PM

TimT,
Don't know how many 911 lube systerms you've taken apart, but I have the skinned kuckles from many instances. The big metal scavange pipe from the side of the case runs directly to the ext thermostat, where the oil therein either takes a left turn to the front cooler if the thermo is open, or a right turn to the filter if the thermo is closed. Hate to burst your bubble but it's not "filter first". End of story!!

TimT · 07:38 PM

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uwanna · 07-19-2009, 06:27 PM

TimT,
I apolojize, didn't mean to impune your knowledge or integrity. I can see by the tags below your signature, you must have a great deal of knowlege of 911 stuff.
My only concern is, I can't conceive of a method in which the oil could go to the filter first them somehow get to the front oil cooler from a pool of oil in the tank which is no longer under pressure. If you can show me how, I have an open mind!

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by TimT

a bunch

TimT,

The pictures attached by Uwana and Jascha are good representative illustrations for SC's engine while your picture is very misleading. It does not even have an auxiliary thermostat. The engine oil is pumped by the scavenper pump directly to the auxiliary thermostat.

The auxiliary thermostat is normally open and delivers the circulating oil to the oil tank (oil filter). The auxiliary thermostat does not come into action until the circulating oil reaches 170°F-180°F. So for cold engine, the flow of oil from the scavenger pumps is aux. thermostat to oil filter (oil tank). But for warmed engine, it's auxiliary thermostat to auxiliary cooler back to aux. thermostat and finally to oil filer in the tank.

Tony

TimT · 07-19-2009, 07:42 PM

I'm thinking I am done with this forum

the picture I posted and the description are right out of the Porsche workshop manual.. I posted above that I was going to get all the iterations of the oil system scanned.... don't think so anymore

adios...

uwanna · 07-19-2009, 07:55 PM

[QUOTE=TimT;4786276]I'm thinking I am done with this forum

the picture I posted and the description are right out of the Porsche workshop manual..

Yeah, a manual for a 42 year old 911 before external oil coolers!