Instruments

[IceMan]

I couldn't really find a spot to post this so if the moderator wants to move it to its proper place, please do.
I am in need of some mental jogging or maybe just a plain boot to the head. My problem is that my temp gauge is reading 20/30 degrees to high but with the infrared thermometer says it is running at 170. First, the things I have done. Pulled the sender out and removed the teflon tape and thread sealing compound and reinstalled. Still read wrong. Replaced the sending unit. No change. Removed the old/new sending unit and gauge both Steward Warners and replaced with Teleflex units. Still no change. Then checked all the wiring between the units, replaced wiring and connectors according to ABYC regs. No change. Removed any and all ground connections and cleaned them. Then ohmed them out, all 0.00 ohms. Still runs 20/30 degrees high while at the sending unit it is 170 with the IR. So..... I'm at the end of my ideas.
Can anyone think of what I haven't done, or done wrong or just haven't thought of? Any and all help is appreciated.
WD

[Astrid]

Where are you taking your IF readings from? Typically the temp gauge is measuring the coolant as it is about to exit the engine and circulate through the heat exchanger. You can take your IF reading just about anywhere, and you will get different readings from different points on the engine. You may also be getting variation due to the fact that metal is dissipating heat at a different rate than water coming out of the waterjackets.

[IceMan]

Astrid,
I thought about that too, so I use the IR on the sending units base itself, on the thermostat housing below the thermostat and the housing above it. They all read to within 5-8 degrees difference.
WD

[justlearnin]

Ok this may be a bit of a stretch but you are obviously a patient and methodical peson so I'll bite. Could the thermostat housing temp sample point (inside) be at a bit of a dead flow spot inside the housing. Or is it at a place where the water just doesn't flow all that well and the senders aren't cooling inside and the outside has air current to help cool or perhaps your ir termo is made in china and therefor a POS?