Wonky Temperature Gauge

[Tactical Bacon]

So, I did a search of the forum, found a few threads with a problem similiar to mine but slightly different, so I wanted to make sure I had the right answer to my question before moving forward. I noticed the other night when I was driving home that my temperature gauge was fluctuating. Nothing drastic or rapid, just want to keep my eye on it because I don't want the engine overcooling or overheating on me. What it was doing is the needle would stop right below the 210 mark on the gauge then slowly go down to right above the mark between 100 and 210 on the gauge, then go back up. It did this if I was above 45 mph or so. Below that speed, it would only go halfway to the lower mark then go back up and the needle moved more slowly. If I go below about 10 mph or just sit at idle, it still goes down to about halfway between the marks but it does it very slowly.

 

I'm fairly certain it isn't electrical due to the differences of gauge behavior at different speeds. I suspect a bad thermostat, a faulty coolant mixture or dirty cooling system (looks like dirty water in the overflow tank and radiator), or an inaccurate but responsive gauge.

[gogmorgo]

Something I learned the hard way this week: always know exactly what you're running for coolant. It might not mean much in your climate (don't know how cold it gets there) but an insufficient amount of antifreeze due to me not properly labelling my emergency stuff and assuming it was properly mixed lead to me stuck on the side of the highway in -30F windchill for several hours while I fixed three blown hoses and walking a couple miles to a gas station to get more anti-freeze. My heater and overflow hoses were frozen solid.

 

Thermostats are reasonably cheap (less than $15 up here got me both the thermostat and gasket) and are easy to change. It's pretty well standard procedure up here that "oh, your temperature is weird? Here's a new thermostat."

Also, I've experienced similarly fluctuating temperatures while low on coolant. The temperature would climb, the aux fan kicked on, and then the temp went back down. At higher speeds, there's more air flowing through the rad and thus more/faster cooling. I had a hole in my rad which leaked about a gallon an hour, and when the temp gauge started doing that, it was usually down about three pints. Because it was pushing pressure out of the hole in the rad and then sucking air in through the same hole, the level in the overflow bottle never changed.

[Tactical Bacon]

I think what I was running was rusty water. As far as temperature goes around here, it tends to stay above 0* F. Last night got to about 20*. Friday night when I got home from work I opened the drain on the radiator and added a gallon of yellow (yes, I know the universal is complete and total $#!& but this is just to hold me over until I get a system flush in 12 days) and about 3 quarts of water (tap, but like I said, professional flush in 12 days). I'll probably swap the thermostat before I take it up to the shop for a  flush so I know I have at least one good component.

 

As far as overall temperature, it's been staying below 210 on the gauge and the aux fan hasn't kicked on except for when I turn on the A/C/Defrost. No leaks in the coolinng system. Only leak I have is a slow one somewhere in the clutch hydraulics but that's a problem for another day.

[92tanMJ]

First off drain the hard water as it will kill your cooling system. Replace it with 50/50 or the whole stuff and use distilled water you can get at kroger or whatever for like a buck.

 

Secondly, if I had to guess, I would put on its the sensor at the rear of the block RIGHT next to the firewall.  Mine had the random jumping problem and that solved it. You could alway change the one in the front out as well...but again I would put money on it being the one in the back.

[Tactical Bacon]

Pretty sure that joker has been running nothing but hard water since before I got it. 10 days isn't really going to make much difference.

 

And it isn't random jumping. It's a consistent movement between 210 and the mark between 100 and 210 on the gauge that varies in how rapidly it moves and how far it moves between those two marks based on the speed of the vehicle.

[gogmorgo]

I'd worry about getting a decent mixture in there before anything else, except maybe the thermostat. Like I said, they're cheap and it only took me ten minutes to do mine, and that was mostly due to the cold. (see the above scenario)

 

If it regularly gets down below freezing, then it's highly unlikely the truck would have survived very long running water unless it was never parked outside. Rusty water tends to mask whatever colour the antifreeze mixture is, and my limited experience is that people usually don't bother thinking about their coolant unless it's all over the road.

My "chosen" antifreeze is the green Prestone extended life (in a yellow jug), but I really only go with it because there's always a huge display right inside the door of my favourite parts chain so it's convenient to grab. Oh, and I like the bright fluorescent green in my overflow bottle... 

[Tactical Bacon]

If I had the time, I'd flush the coolant system myself, but I have no time because I go to college full time and work 30+ hours a week in addition to playing taxi driver for my sister. Hence I have to wait 9 more days for my next paycheck so I can take it to a shop to get a professional flush done (and buy the new thermostat). The gallon of the prestone universal (not universal at all) garbage is just to hold me over for the interim. I would have gone with conventional green if I had known for sure there's no orange/red/pink in the cooling system whatsoever.

 

I bought the truck in July where it stayed above 80* at night. I live in TN. It only started getting below freezing in the past week or so.

 

As far as why that yellow jug of prestone is garbage and nowhere near universal, here's the short of it:

Green is IAT (inorganic additive tech). Has silicates and phosphates. Ethylene glycol. Good for iron blocks and aluminum heads. Needs to be changed every 3 years/36k miles or so.

Orange (dexcool) is OAT (organic additive tech). No silicates, low phosphates. Long life stuff. Good for 5 years/100k miles and less toxic to the environment. Propylene glycol based (PG). Problem is exposure to air tends to get it sludgy and that will happen in any non-pressurized environment (including overflow bottles in open cooling systems) and that will get sucked into the cooling system and block passages or if you get an air bubble in the engine, sludge can form. Of course, keep your system topped up and change it at the proper intervals, and these problems tend to dissipate.

Red, pink, green, gold, blue, etc. (VW, Mercedes, Chrysler, Ford, etc.) tend to be HOAT (hybrid organic additive tech). Has low silicates and no phosphates. Also PG based. Doesn't sludge up, 5 year/100k interval, overall pretty good stuff but pricey.

The problem you get with the universal. It says that it's safe to mix with anything (bull$#!&) and meets OEM specs (mega bull$#!&) but it's really an overglorified OAT (not Dexcool or Dexcool approved). The universal has a bit of everything. It is PG based (if OE specs call for IAT it has to be EG), it has silicates (OAT has no silicates), and it has phosphates (HOAT dictates no phosphates). The reason OEM specs hold important is because some additives (like EH2, found in dexcool that helps combat corrosion but acts like a plasticizer and ruins gaskets in some engines) don't play nice with other engines and their bits and pieces. Gaskets, radiators, radiator solder, plastics, etc. And running it by itself can be risky, too, since it may not play nice with your bits and pieces.

 

Will you see any damage or problems manifest? Can't really say. But the universal junk is just there as a holdover to get you to a shop so you can get a proper fix done on your cooling system.

[Eagle]

It sounds to me like you have a lazy thermostat. The operating temperature doesn't stay constant -- the thermostat constantly cycles open and closed. The purpose of the thermostat is to keep the temperature UP, so if the cooling system is working, the temperature will get up to the setting for the t-stat, the t-stat will open, and the temperature will then drop to the point at which the t-stat closes again. Then the temperature goes back up until the t-stat opens. Rinse and repeat.

 

The normal range, IIRC, is only about 15 degrees or so and most people don't notice that amount of change on the temperature gauge. Your thermostat may be allowing the temperature to drop too far before it reopens.

[Tactical Bacon]

It sounds to me like you have a lazy thermostat. The operating temperature doesn't stay constant -- the thermostat constantly cycles open and closed. The purpose of the thermostat is to keep the temperature UP, so if the cooling system is working, the temperature will get up to the setting for the t-stat, the t-stat will open, and the temperature will then drop to the point at which the t-stat closes again. Then the temperature goes back up until the t-stat opens. Rinse and repeat.

 

The normal range, IIRC, is only about 15 degrees or so and most people don't notice that amount of change on the temperature gauge. Your thermostat may be allowing the temperature to drop too far before it reopens.

 

I appreciate the second opinion. I honestly wouldn't be surprised if it's the original thermostat in there, judging by the rest of the jeep haha.

[Eagle]

Just noticed I had that backwards. The thermostat is open while the temperature drops. It would be staying open too long before closing.

[Tactical Bacon]

Just noticed I had that backwards. The thermostat is open while the temperature drops. It would be staying open too long before closing.

 Yeah, I noticed that but I decided to see if you would catch it, too. :thumbsup: