1.6 runs hotter with new 71° thermostat

[jhax]

I recently replaced my 87° thermostat with a 71° after it finally broke on me. I have noticed that my car's temp fluctuates much more and gets much warmer much quicker than it did with my old thermostat. I figured by buying a lower temp thermo that it would make the car run cooler. I used g11 coolant roughly 60/40 mixed thinking it would help but it hasn't. My fan kicks on when its supposed to. What could be the issue?

Justin

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[bajacalal]

Is it even running too hot?

With a broken thermostat it was possibly stuck open and never fully warned up. Antifreeze actually has worse cooling properties than water, adding more antifreeze will raise the running temperature (though usually only slightly), I wouldn't recommend more than 50/50 for warm climates.

[theman53]

I run the same t stat and mine runs about 180f all the time at the head. FWIW unless you are pouring the fuel and have super high EGT there is no need for the cooler stat and you will get worse mileage than if you ran the 180 or 195 t stat. That said I think Baja is on track with the partially stuck open. Also, until you get a real gauge it is kind of relative. Especially if you flushed the system out and have better contact with the coolant sensor. 

[jhax]

Compared to what it was before its running too hot. Driving up hills that little gauge shoots up there. Not blinking led status but just below the line. I knew our tstats stuck open usually but I don't know if that's the case with my old one, it wasn't letting coolant bypass allowing it to heat up and make my rad hose split (the little one in front of the block). Although I could be wrong. Maybe the hose split and screwed up the tstat. I'll balance out that ratio and see where it gets me.

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[theman53]

How long has it been installed and did you boil it to see if it was DOA or not before installing?

[jhax]

I put it in 2 weeks ago. New from car quest. Unfortunately I did not test it. However I believe I found the problem. When my car originally overheated it caused my expansion tank to split at the seam on top. I can't put coolant in it above the minimum fill line just above half way. It leaks if I do. I'll make a trip to the yard and get another one.

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[vanbcguy]

For my Mk3 a new coolant reservoir was about $15. Just something to think about before spending a bunch of time in a yard grabbing something grubby.

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[theman53]

https://www.autohausaz.com/search/product.aspx?sid=pxkcijvdsokngoifayexniik&makeid=800026@VW&modelid=1282845@JETTADELUXE&year=1986&cid=16@CoolingSystem&gid=10457@ExpansionTank/CoolantReservoir

[jhax]

Right o, thanks. On a side note. I assume 4 door jetta headliners fit 4 door golf roofs.

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[TimpanogosSlim]

Right o, thanks. On a side note. I assume 4 door jetta headliners fit 4 door golf roofs.

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iirc for mk3 the 4-door roof is the same for golf and jetta. i think for mk4 as well. dunno about the others.

[jhax]

Got it all figured out. Definitely the leak in the coolant tank. Thanks all.

Justin