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engine temp discrepancy

B

bobct

Advanced Contributor
I'm wondering if you guys can take a look at these numbers and tell me what you think. I had a temp issue last year when Diver Dave identified that one engine was running actually too cool. I fixed that by replacing the new thermostat which I apparently installed with a sledge hammer.

I ran last year w/o any issues but one engine "seemed" to be slightly hotter than the other. The readings I get with my IR gun don't really tie out with what I see on the gauges though:

Port Stb

160 (Temp gauge) 170 (Temp gauge)
162 (Temp sender) 150 (temp sender w/gun)

Gauges and matching temp senders are relatively new. So, the Stb engine seems to run about 10 degrees hotter at both idle and cruise but the temp sender reading seems to be too low. Port side seems to be just about perfect. I cleaned up both ends of the wiring so they're nice and shiny. The other readings I took were both sides manifolds and risers. The risers on the Stb engine are actually cooler but one manifold is about 12 degrees hotter at 190. All of this was done on the hard at idle but no reason to believe it will be any different than last year.

Bob
 
TEMP #334AD

100 412
145 230
190 137
235 85.9
280 56

Bob; here are the resistance vs. temperature values for a single station engine sender for Stewart Warner. You might graph these into Excel to see an actual curve. Dual station will be different, however.

I like to look at cruise temperatures before any work is done. Except, obviously, if there is a major issue or boiling, etc at idle.
Another thing you could do is to disconnect the wire at each engine temp. sender and clip on a 220 5% resistor, the other side of the resistor the to engine block. Do you get near 150 deg at each gauge?
 
Last edited:
I use a 110 ohm resistor, in place of the sender, and they should 1/2 scale on the 'american' calibrated gauges. 33 ohm should get you full scale though many 'approxiamte' this with a short.

the other thing to remember is the 'ground' side of the circuit...any marginal connection will only make things 'colder' on those gauges. (seems NOT to be the case here).

Like DD, I'd run things under load (cruising on plane) to make sure you understand the steady state of the system.

The last item is that these gauges are notoriously inaccurate...you may wanna swap the sender leads between both gauges to see is the anomoly stays with the gauge or the sender/wiring...not comprehensive but another source of data
 
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