Please don't dogpile me for asking this question...

[ubtripn]

But I have been dealing with cooling issues and I realized that I needed to check the gauge so I laser measured one inch from the thermostat housing and then the hose connected to it and both were 20 degrees lower than what the gauge was reading. It a mechanical gauge with an ether filled line. I then noticed I have it between two headers and wondered two things:

1. Am I measuring the coolant or the oil by having the sending unit there and

2. Has anybody else ever seen a discrepancy this large?

I ask because I may have been spending a lot of time solving a problem that does not exist. Thanks for your expertise.

Also, cood the proximity to the headers be impacting the reading. Thanks again.

[A1971Blazer]

Are you boiling over? If not, you probably don't have an issue.....
a mechanical gauge might pick up heat from the headers?

[ubtripn]

No boiling over so I think my gauge may be off.

[A1971Blazer]

what temp is the gauge reading?
If you're getting over about 225º-235º your radiator will start to boil over.....less than that with a bad radiator cap...
sounds like your gauge may be faulty....

[67ChevyRedneck]

Pic of where it is. I think I have mine in the same spot and mine reads correctly, but I don't have headers. You can always crack it loose and see if oil or water comes out

Insulated heat tape isn't too expensive. Put a couple wraps around the line where the header is. I've never heard of a gauge with an ether filled line, so it is entirely possible the header heat is warming the ether in the line causing the false reading? Again, I've never even heard of this type of gauge.

Mechanical gauges are cheap, if the tape doesn't work, swap it and see what happens. The only thing that sucks is where it's at, you need to drain over 1/2 the coolant out, or try to swap it as fast as possible

[ubtripn]

Great advise! I haven't boiled over. I think it is almost exactly 20 degrees off. I now measured both at different temps and always had that difference. Its not boiling over so I think I will pull it and see whats up, thanks!

[Gromit]

Ideally the gauge and sending unit need to be matched but that is not always the case since OEM sending units are NLA for the most part and it sounds as if you are using an aftermarket temperature gauge.

You can check some of the archives here for threads where members have gathered data on the behavior of their sending unit by putting it in a pot of water on the stove with a thermometer and compared the resistance (or is it impedance?) to what the (OEM) temp gauge wants. I believe you can adjust the temp gauge with a resistor until it reads accurately but I haven't done it.

BTW, you don't have to worry on this site about getting trolled - people here try to help - don't mess with the site administrators though you really have to be bad to tick them off.

[Coley]

I always try to have, source or buy a few spares of certain things in case I have to do some troubleshooting.
This gauge would be a good example....easy to come by, see them all the time at swapmeets. Other 'handy' spares include a good alternator and regulator...just for some handy quick testing sometimes.
Sounds like you have it worked out!

All Good
Coley

[KRamsey07]

Mechanical gauges now are horrible... I work for Cat and when we set up hydraulic pumps we would install a gauge and set at the recommended pressure . During a quality gate we used a different set of mechanical gauges from the quality lab they would show 2-300 psi difference well passed an acceptable level . So we started watching pump and valve settings closely id even take pictures. Then they would fail at the quality gate . We got the gauges calibrated monthly and was kind of dumb founded . So in my infinite wisdom ( sarcasm) i decided to get new gauges and they would read 2-300 psi the other way ... tried another set 2-300 the other way and so on... After talking with the manufacturer of the gauges they would only guarantee the gauges in a controlled climate of 75 degrees which is not what we where doing and the filler liquid ( glycerin ) is very temperamental . To make a long story short we got a set of digital gauges and life was good . I guess the point im getting at is the gauges where not cheap and from a reputable manufacturer and would still read differently depending on the conditions they where in and i believe this applies to most mechanical gauges used .

[prodjay10]

I get the same temp difference with a laser thermometer pointed at the thermostat housing. I believe it to be because it's not measuring core temp. It's measuring surface temp. And it's possible the surface color/ texture throws off the reading.

[ubtripn]

Great information. I don't know why I accepted the reading as gospel and went straight to troubleshooting everything BUT alot of stuff got upgraded which cannot hurt so it was all good in the end. This board has proven invaluable to me, thank you all!