Slappy3243

Yeah, I don't remember this happening previously so something is up. I think it is the thermostat. I will try to check the gauges in "Touring" mode on my ride home to see if I can get a digital read.

As far as the problem goes - is this something that can wait until my next oil change? My mileage is the same as it was before and there are no check engine lights. I would rather get this done during a routine oil change to save me some time.

NSC5

As long as it is hanging up open rather than closed it shouldn't be a problem as long as your next oil change occurs before the outside temperature really starts to fall. But keep an eye on the temperature because a thermostat that is sticking open likely has an increased chance of sticking in the closed position.

Slappy3243

Keeping in mind that I do live in Florida, I am not too worried about the temperatures getting too cold . I grew up in NY so the case would be quite different during a cold spell there and potentially not having effective heat in my car.

I really appreciate the help. I will update this thread with any updates when I have them. I think my oil life monitor is at 80% right now but I drive a lot.

Thanks.

hangman

Hi Slappy, here is the link to my thread.

https://www.corvetteforum.com/forums...d-driving.html

What I find is that the indicator is as mentioned, dependent on engine temp. I have monitored it and as soon as my engine temp hits 180, the yellow line goes away. As soon as it drops to like 168, the yellow line appears and the engine would then take a few seconds to warm up to 180 and the line would go away again and vice versa. This condition only happens and show up when the outside temp is cool, usually in the 60's or lower, and only when I am cruising or the rpm is not very high. Which makes sense to me since this would cool the engine back down to 168 and then it warms up again and vice versa. I live in Houston and this does not happen in the summer time since the temp usually is around 190 or 200 during normal driving in the summer. I did compare it to another C7 of a friend and his does the same so I figured it was normal and I also like my engine to run a little cooler around 180 anyways.
The odd thing is that this appears only when the instrument cluster is in the sport or track display. The yellow line does not reappear after the initial warm up in the touring display tach.
Note, my car has behaved this way from new and since the yellow line at 3500 rpm doesn't go away until after the first 500 miles, that's when I first noticed it.

Slappy3243

Thank you for that link and information. Yes, this started here with my car when the temps dropped recently, but I don't remember this happening other years. Also, my head's up display actually does match the tach when this happens. It's very subtle since the fluctuation is small, unlike when the car is first warming up from cold.

Slappy3243

I monitored the temps in touring mode last night. The engine temp stayed between 172 and 176 degrees while driving on the highway, well below the 190-200 degree range it should be at. This explains the tachometer lines. Oil got to about 180 degrees.

Thank you guys.

NSC5

Glad you found the digital display Slappy. Much of the menu system is anything but intuitive with the C7.

At some point the engine cooling temperature will be sustained at a point low enough to create an error as people installing 160 degree thermostats have found. When that happens your digital temperature readout will go to zero and the analog gauge will stay on the lower peg, the cooling fan will also continue to run when the car is shut off. The controller leaves the fan on because it assumes that the coolant temperature sensor may not be reading correctly. So don't panic if this happens because you can still drive it to the dealer but it will be time to get it replaced at that point.

Slappy3243

I appreciate all of your feedback. I'll update here if anything changes.

Flame Red

Funny, a lot of people run a 160 stat. I don't see them mentioning this, but some do report they do get some message (or code?) indicating that the car is not warming up.

I have run a 180 stat without this issue. I am now trying a 170 stat for the last couple of weeks and have not noted this behavior - yet. No tune.

DanZR1

Kinda off topic, but when the car is cold, and the red line is at 4500, will it shut off the fuel at 4500 RPM if you floor it? Always wondered about that, but don't really want to mat my throttle on a cold engine...

NSC5

The warning line is advisory only, the fuel cutoff is still at the normal redline RPM.

The tach warning line is a nice reminder but I like the oil temp to be up to 170 before I go to higher RPM and it will lag the coolant temperature quite a bit during warmup; at least with dry sump engines.

Roly16

KenHorse

If not he's been driving it that way for more than a year

JerryU

You need a replacement thermostat regardless what the OP did!

These engines are not designed to run that cold unless you are looking for more power and have a tune increasing timing etc.

AEK

So, I have exactly this problem, and have had it since I bought my 2014 Z51 LT1 used last year.

The one non-stock feature of my car is a nice aluminum radiator (I forget if it's a DeWitt or the other brand).

In slow traffic, around town, at idle, driven hard, etc. the engine always sits at 210-220F, on the real water temperature gauge on the right.

When I bought the car, it was previously a track car, with Mobil 1 15W-50. I had an incident one 49-degree evening, where the engine went "too cold" and into the mode where all the fans went on (this is mentioned earlier in this thread), etc. I limped home, and ended up replacing the thermostat housing and thermostat (the old one looked OK) with the stock GM part, replaced the lost coolant, etc. Before and since then, on any day while cruising, the coolant temperature will ALWAYS drop enough to trigger the "yellow bars", if/when I am cruising in 6th or 7th gear. If I drop down to 4th (or sometime 5th), the yellow bar will go away after a short while. This is with outside temps in the 50-to-80-degree range, day or night, etc.

A few days ago and around 1500 miles into owning the car, I switched to Mobil 1 5W-30 (Dexos 2, yadda yadda yadda). The problem seems even worse now -- as an example, from a fully warmed-up engine in town (210-220F on water, mid-gauge on oil temps) on a 39-degree night, I drove home at highway speeds for around 35 miles and light throttle in the upper gears, and by the time I got home, the water temp was had fallen to around 160F, and the yellow bar had rotated CCW almost to the 12 o'clock position (just a little bit to the right of "4" on the tacho).

So, I'm kinda at a loss to understand this. I really can't believe that this aluminum radiator is so insanely efficient that it just sucks the heat of this engine in this manner. Furthermore, I thought C7s have 180-190F T-stats, and so 160 is on the low side (but may be incorrect, I need to use that other dash mode).

I really doubt my T-stat is stuck, since in all other situations except high-gear highway cruise, temps are stable at 210-220F. And I've seen the exact same behavior through two T-stats, both of which appear to be identical.

What am I missing?

Mobil 1

If the thermostat was sticking open it would throw a code.

Mobil 1

Nope.

JerryU

FWIW, it could be sticking. Easy enough to check and not guess. Did it when selecting the proper thermostat for the 502 cid engine in my '34 Ford. In fact found a thermostat that had a wider, quicker opening NOT just the correct temp. It is a "range" NOT an instant temperature where it operates. The thermostat could be starting to open early. Could try a higher quality thermostat than the GM part. I found a Robert Shaw thermostat had a narrower opening range. Check with Jegs or Summitt tech folks (google for 800 #) and get the correct one.

This is a procedure I just copied:
Thermostat Testing

Unlike many other parts, you can’t just look at a thermostat and know if it is good or not. Thermostat testing is easy and it is kind of cool to watch, at least it is if you are a gearhead or science nerd. All you need is glass jar, some tap water, a microwave (or stove/hot plate), thermometer (not from your medicine cabinet, a diagnostic thermometer or a cooking thermometer), and a thermostat.

Start by inspecting the thermostat. If the unit is open at room temperature, then it is bad, and you need a new one. Sometimes they get stuck open, this is usually due to the wax on the inside leaking and when it hardens, it pins the unit open. Once this happens, it is junk.

Fill a jar, pan, or bowl with tap water and heat it until it is at least twenty degrees above the open temperature of the thermostat. You can do this on a hot plate or stove with the thermostat in the water, but it is best if you heat the water by itself, and NEVER put the thermostat in the microwave.
Carefully lower the thermostat into the water. Use the thermometer to monitor the temperature of the water. Watch the unit slowly open. The water needs to be at least 20 degrees hotter than the unit’s rated temp. If the unit does not open at all or does not fully open, it is bad.
Continue to monitor the thermostat as the water cools. Once the water temp is exactly 20 degrees above the rated temp, the unit will begin to close as the temp falls. Note the temp when it starts to move and when it is fully closed. If it is closed with three degrees of the rated temp, the unit is good.

PS: I just used a shallow pot on the stove and watched the opening and closing range as the temp increased and then decreased.

Roly16

JerryU

Interesting observation BUT....expect the viscosity at 200 F operating temp is not much different from 5-30 or 0-40! It's at the extremes where the differences occur.