Issue With Coolant Temp. Sensor

fish1 · **Posted:** Mon Mar 11, 2013 3:01 pm

My coolant Temp. gauge started giving me bad readings about a month ago so today i pulled the sensor and this is what i found ! It only seems to be on the brass i pulled the upper rad hose at my inline tstat and it was clear any ideas ?

kjjet · **Posted:** Mon Mar 11, 2013 3:46 pm

Clearly somthing in the coolant system is attacking the brass. What mod did you do to install those brass fittings? May not be a good idea? Blocks or restrictions are bad. When was the last coolant change? I see you have a inline thremostat including a housing. That looks good.

papaindigo · **Posted:** Mon Mar 11, 2013 3:58 pm

It appears that you have installed a temp sending unit (after market? to a auxillary temp gauge?) to a brass/bronze "T" fitting in a coolant line. I'm not sure why as the stock tstat housing has a temp sending unit mounted in it and while the OEM gauge is not marked in degrees there is a GDE post showing the temps at different needle positions. That sending unit is easily replaced if it's a problem.

Setting the above aside you have what appears to be a classic example of galvanic corrosion with the corrosion attacking the brass/bronze. As to why I don't know; not my area of any expertise. Are you using a proper mixture of HOAT antifreeze? Is that antifreeze so old (over 5 years) that it's corrosion prevention properties are gone?

Off hand I'd flush the coolant system (you can purge all the old antifreeze by doing several cycles of drain and refill with clean demineralized water before a final fill with 50/50 HOAT and demineralized water) and I'd personally recommend removal of that fitting and sending uint; replacement of the cut hose the unit is installed on; and just use the stock tstat mounted temp sensor and gauge. I'm pretty sure the stock gauge is what lets the ECU know when to cut certain systems to prevent engine overheating; if so that sensor is critical.

fish1 · **Posted:** Mon Mar 11, 2013 4:37 pm

I did a flush and fill about 4 months ago with Zerex G05! It appears to only be on the brass, im going to do away with that fitting.Should i do a complete flush and fill again?
I had a mechanical temp gauge before and changed to a electrical gauge it appears this is when it started to do this because when i pulled the sender for the mechanical gauge a few months ago everything was clear.

dgeist · **Posted:** Mon Mar 11, 2013 4:39 pm

<edited original post so images would appear>

You may be circulating small bits of aluminum (or maybe iron..) and the pH of the G05 is favorable enough to have a reaction where they hit the brass. Here's the milspec reference on what metals tend to react to each other when in direct contact in an electrolytic solution.

http://www.wbdg.org/ccb/FEDMIL/std889b.pdf

It would be better use an Aluminum or stainless fitting where possible, based on the similarity of metals, and it would be good to drain and refill anyway at this point and ensure you get the 50/50 right and that you flush everything out. I like the pre-mix for that reason even though it's more expensive. The fact that the brass doesn't have an electrical ground bond to the block may have accelerated the reaction, too. A high-temp plastic fitting may actually be your best bet in this case.

Dan

Issue With Coolant Temp. Sensor

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