Low (Cold) Water Temps while Driving
 

So I am having a weird issue that I couldn't find anywhere while searching the web and here.

It is relatively cold here in GA/AL right now at 40 degrees or so. I let the car warm up to 80 Celsius and start driving. I'm doing 55-75 mph driving back roads and highways and the water temps drop to 67-71 degrees Celsius while I'm driving. It warms up while I'm stopped never went over 84 C tonight. Air Intake Temps were around 16 Celsius too.

Shouldn't the thermostat keep coolant from flowing and allow the car to stay warm during operation?

I've never seen this before...

Actually, I have the same problem. For whatever reason, my V-mount setup almost causes the engine to overcool, especially on the highway (although the turbo still smokes due to oil stains...).

I've never seen my electric fans running, even after driving on the track. I'm not sure they even work.

What temp does your car get to when you just let it idle?

I don't know if my car even has a thermostat.

Could be that the thermostat is either stuck open of bypassing too much. The way to check would be to pull the thermostat and look to see if it is stuck. It should be closed when you pull it, then drop it in a pan of water with the thermometer and stick that one the stove and note what temperature it actually opens at. Of course this requires draining coolant and pulling the thermostat so you might want to rule other things out first. An infrared thermometer might be another way to check this although with less accuracy, read the temp of the parts before and after the thermostat.

Could also be the temperature sensor or circuit is bad causing the wrong ready. They decrease resistance as they get warmer so a high resistance fault(corrosion, loose wire contact, etc) would cause a lower temperature reading than what it really is. Again an infrared thermometer would help because you can see if the actual engine temperature with it matches your ECU reading from the sensor.

I don't think this is uncommon at all for v-mount set-ups and I have the same issues with water and oil temps being too low. I doubt you have an electrical issue. If your cursing at 67c at high speed you should see your rear iron temp reading, gauge cluster water temp, get very close to the bottom.

I have been breaking in a new motor so I have been really trying to keep temps where they need to be. Early morning temps where I am at are in the 40's and get up to mid 60's during the afternoon. To keep my temps higher I had to cover 30% of my radiator and 70% of 1 of my oil coolers with cardboard. This is all city stop and go driving with no freeway driving at all. If I was doing mainly high speed freeway driving I would have to cover more.

So I think it is most likely the thermostat, even though it is new. It was not a bad sensor reading. I would stop if it got into the 60s to warm back up. The water would be cool enough that when I cracked the AST then the cap, the coolant was hot but not scolding. The heater air would be cool until I warmed it back into the 85-87C range.

My car has a FMIC with some very good sheet metal ducting for the radiator.

During my drive yesterday I stopped at a Dollar General and borrowed some old cardboard to block off the IC ala redneck truckers up north. That did the trick as the water temps went up and stayed around 90-92C. On the way home I blocked off only half of it and my water temps were 81-84C.

I have 2 oil coolers so maybe I should get an oil temp gauge too....

sounds like the thermostat, OEM is an NTC brand

Add another vote for t-stat not working properly

I saw your old thread that had an oil temp sensor in the oil plug location, but the link was dead. Do you have that info still and how did that sensor hold up?

Mine does the same thing. Temps below 170 driving on the highway. If I come to a complete stop the thermostat opens at the temp prescribed in the FSM and closes as per manual too. I measure temps from the throttle body coolant line.

same here as the op. highway driving during this weather my water temps are stable at 79C and oil at ~165F. at idle the rad fans will kick on and my oil temps go to ~180F then the thermostat opens and it drops back down to ~170F. i thinks its just the overwhelming efficiency and cold air. my thermostat is brand new so i know it works and my car also has a front mount. im also using twin mocal 19 row oil coolers. my air temps also stay below 20C. i believe everything is working normal, its just the weather.

I think so to since my car functions normally at idle. I have dual 25 row oil coolers with a 180* thermostat too, but I don't have an oil temp gauge...need to get one of those now too!

Still there, and working fine after 14 years.

Here's a link to a similar sender:

https://www.summitracing.com/parts/v...FQIRaQod63wM5Q

You will have to check with them to see if the threads are correct for FD.

By the way, how long should it take for a stock FD's fans to turn on when idling?

It's kind of of hard to answer that question. There's a lot of variables that can affect that. On my power fc, my fans are set to come on at 85c. On cold days like we've had, it takes a while to get to that temp since if my car is idling for whatever reason I have the hood open. I also have a lot of cooling upgrades. I can time it for you next time I'm just sitting around.

Apparently a stock FD's fans don't kick on till around 95c, which just seems absurdly hot. So hot that I've never seen my fans move (even after a track session), and I'm not sure if they even work. I don't want to let it get any hotter than that on the off chance that they ARE broken.

Unfortunately the PFC controller doesn't have fan temp settings (you have to hook it up to a computer to do that), so I can't say for certain what mine is set for.

My car sat for several years so it's totally possible my thermostat is stuck; presumably stuck open, of course.

It takes several minutes to warm up to even 75 degrees on a cold day, but I don't like cranking it at all because it's so damn loud. Fixing my exhaust leak should help with that, though..

You could test if your thermostat is working fairly easily with a Lisle funnel just to be sure. Good to have regardless. Makes burping the coolant system super easy.

How would you know?

Well since your coolant system is already burped the only time you will see a good amount of bubbles/activity is when the thermostat opens. When it opens you can look at what your temp is to make sure everything is in order.

So if I open my filler neck (one of these jobs: http://www.auto-staff.net/tuning2/t-9-4_2L.jpg) when the engine is cold, no coolant should come out or be flowing?

If you have dual oil coolers, you need to block one of them for winter.
Otherwise you oil temps will be to low.

The link is not working for me. I have not seen a factory coolant system in quote awhile but for my set up I could connect the Lisle funnel to the fill neck. While the car is warming up, the coolant will expand and start to fill the Lisle funnel. By the time thermostat is ready to open there should be enough coolant in the funnel to see bubbles emerge from the thermostat opening. This should happen at the temperature your thermostat is supposed to open.

I had the same problem, pulled the thermostat out to find that some genius had drilled 5 holes in it . Put in a new thermostat and sits on 82 degrees all day. And do the fan switch mod u wont regret it!

http://www.auto-staff.net/tuning2/t-9_4.html

It has one of these filler net AST combos (with a plain threaded cap), but it also has a separate AST with the pressure cap.

A stuck or poorly functioning thermostat is really the only explanation. Even if you have the most uber awesome Vmount setup; it doesn't matter. The radiator ONLY comes into play when the thermostat is OPEN. Thus, when it's closed, pretty much all the coolant is just recirculating through the engine (not the rad) and it wouldn't matter if you had a radiator the size of Texas. If your t-stat is on the fritz it won't be able to control how much coolant gets to the radiator and could end up overcooling the car.

And can I just say....this is the first time I've seen the term "Overcooling" has been seen on this forum in probably a decade. What sorcery is this?!?!

Some folks drill a few small (2 or 3 3/16" diameter) bypass holes in the thermostat to make warm-up more linear and stabilize coolant temperature on cars that are used for track days or races. In cold weather that can make them run too cold, similar to a stuck-open thermostat.