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Old 11-23-2015, 09:46 AM
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water temp fluctuates

Driving my 2012 5.7L in 22F ambient temp on hwy I realized it was cycling the water temp from 199-222 very rapidly, like within a mile. It keeped going up and down, is this normal, or am I heading for disaster? Any thoughts? Newer water pump, and fluids are full and fine.. It does the same thing at idle too as the fan turns on and off, I've noticed.. I've never seen it do it on the hwy though.. Thanks.

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Old 11-24-2015, 11:10 PM
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Re: water temp fluctuates

Bumping myself...

I am stumped about this, but I am wondering if the newer skid plates I added (and I have covered the oil drain plug hole in the plastic front plate to prevent salt spray into the engine bay) are effecting the air flow even on the hwy at 80mph?? It doesn't do it nearly as fast when not moving.
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Old 11-25-2015, 06:37 AM
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Re: water temp fluctuates

How about a stuck thermostat or your water pump failing ? Have you checked your coolant level? Does it have sludge in it?

Not like you modified the car in ways in which was never intended (i.e. skid plates blocking the air flow underneath). Granted that those vehicles equipped with skid plates from the factory typically come with larger radiators. Fluctuations rather than consistently higher coolant temps, at constant speeds, would indicate a mechanical failure somewhere. There's enough air flow to move air past the radiator at 80 mph and enough places for the hot air to escape even with the skid plates.
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Old 11-25-2015, 11:11 PM
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Re: water temp fluctuates

makes sense.

Everything is in good "order". Coolant level and look is fine. What I really need is 2 or 3 hemi owners to cruise on the hwy and watch the coolant temp and see if it oscillates from 197-222F or so, especially at about 30F ambient, like constantly, and at least once a minute. I suspect in order of my own opinion of likeliness:

normal function - or within normal function.

Failing or malfunctioning fan - turning on at 220 as expected, then maybe overcooling and shutting off completely?? Not sure how these work, really..

failing t stat (although on all the sites I've searched people with similar problems with other types of cars had no effect from new t stats!)

Failing water pump - as these fail a lot but mine is nearly new, and isn;t leaking or making noise. Could be faulty replacement as I think it is happening since replacement, but not sure how a water pump could cause this.

air bubble - I've "burped" it without effect, and it's been doing it for over 500 miles.. Seems unlikely.

Oil temp never varies and is always fine at about 190F while this happens.

I'm not planning hwy travel for a while, so I am going to watch it in city driving for a while as it seems fine there...

Thanks..
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Old 11-29-2015, 10:37 PM
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Re: water temp fluctuates

Punchline: T stat..

Replaced T stat and now temp is steady at 206-212. Clearly fixed...

Things learned in this deal:

I think the water pump change at 40K miles was the start of this. Done by my dealer, probably replacing or putting it in the new pump had some cause of this. Although the t stat I removed was in correctly.

The one I removed did have the spring end come apart easily, but not sure this is normal or not. I tested it in boiling water and oven and it seemed to work, but cycled open and closed quickly, just as the symptoms above.. Compared to the new one I also tested, it seemed more "finnicky".

New one was a Murray Plus from O'Rielley's. It is all metal but the OEM has a rubber gasket at the t stat opening part. The new one opened slowly at 203 and not fully in boiling water, needed oven to get it fully open (230F). Initially I thought it was defective...

Replacement was a snap, catching most of the lost antifreeze in a ziplock. Added full strength Zerex G-05 to increase the concentration in my system in my northern state..

Found a SAE article about Zerex G-05 being the same as OEM stuff (at 50% less cost...) Orange Prestone or Dexcool is not the same, apparently, despite many posts otherwise.

Bought a Lisle (sp) spillproof funnel for "burping" the coolant system. Excellent product at 40$. Fits any car and got a lot of air out with no fuss. Highly recommended.

Hope this helps the next sap...
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Old 11-30-2015, 03:24 AM
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Re: water temp fluctuates

For folks who happen to stumble across this later:

The OEM coolant changed for MY 2013, and G-05 (HOAT) is NOT the same as (and not compatible with) the coolant (OAT) in almost all 2013+ FCA vehicles.

See http://wk2jeeps.com/tsb/tsb_wk2_0700412a.pdf
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