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Discussion Starter · #1 ·
It's been going on for better than a year now. Almost daily I get the CEL P0128 coolant temp below thermostat. I top off the reservoir every other day. It only takes maybe a cup or two and its full again. Started this awhile back but it was happening every 3-4 months. It's gotten worse but I can't find a puddle anywhere. Just put the second water pump on couple months ago. Sittin at 310k. Pinhole leak somewhere I'm guessing. When I change the oil I don't believe I see any water in there. Any thoughts guys?


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I am going through the same thing. I changed the coolant, replaced the thermostats, replaced the coolant temp sensor and just replaced the thermostats again yesterday. I hope it's fixed now.
 

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And all of this work was done in the last 4 days.
 

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See if the local part store has a coolant pressure tester for rent. That may help find the leak.
 

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Do you know what your coolant temp is at the sensor? If you log with EFI it will give you an exact temp instead of the gauge.
 

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Discussion Starter · #6 ·
I go off my edge for the engine temp. It doesn't seem to be running hotter than normal. Gonna pressure test soon but am skeptical that I find a pinhole leak somewhere. I haven't done the thermostats ever. I've got one in back and one in front right. Just wanted to bounce this off of the board one time and see what y'all have to offer.


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Start with the tstats. I bought one that had the same issue....fixed the problem. I am betting nearly 100% that is the problem you are having. You still could have a problem if you are having to put coolant in fairly often....but it prob won't throw the P0128 code.
Make sure when you change the stats to put the right one in the back and make sure the holes are facing the right way.....don't want to put it in funky and then have to open it all up again just to adjust it.
 

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You could have bad thermostats - it's an easy fix.

But, you're losing coolant - and, it's going somewhere.
A cup or two every other day is about a quart or so every week.
A gallon or so every month.
Over the last year, that's a lot.

My heater quick-connect ($4.91) cracked last week and the coolant absorbed into the black firewall insulation - hard to diagnose as it probably evaporated every day.
Maybe that's it.
 

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There are two of them for the heater - on the passenger side firewall.
Pretty close to the a/c lines.
 
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