Heater isn't that hot

[marioc89]

It's been around high 30's and low 40's around here and my heater has been working but it isn't getting that hot. I noticed the temp gauge has been sitting around the cold mark and hasn't been moving up to normal temp mark. While it sits around the cold mark, it'll get just warm. It'll occasionally rises slightly above the cold mark and that's when I noticed the heater would feel hotter. Is my thermostat sticking or is my temp gauge broken?

[Towncivilian]

When was the coolant last changed?

Check the radiator cap according to the TSB about radiator cap inspection that's found in the general info thread.

So the temp gauge never stabilizes around the middle?

[marioc89]

I meant to put that in my first post but the coolant is fine. I check it pretty often. I also fail to mention that I don't have a grill on there and no fan shroud because my sister got into a fender bender. But it never stabilizes in the middle while it's cold outside. But if it's warmer then it'll go to the middle.

[Towncivilian]

Maybe the radiator is being overcooled - the grille isn't particularly restrictive, and not having the fan shroud by itself wouldn't cause a very noticeable issue, but the combination of the two plus cold weather might indeed cause the problem.

You have an OBDII reader, right? What's the coolant temp at after 20 minutes of driving?

[marioc89]

I can't remember but when I read it again, I'll make note of it and post the temp. Where should it read?

[Towncivilian]

The thermostat is fully open at 170F but I noticed mine hangs around 176F - 190F. About 152F is where the gauge begins to read "normal". I don't know the upper limit of normal (i.e. when the gauge climbs over normal), I think someone posted it before but I don't remember it exactly.

[marioc89]

Ok. I'll post after I read it.

[CanuckQx4]

Sounds like your thermostat is stuck open (there designed to fail open), and that along with your winter temperatures, the coolant just isnt getting hot circulating through a very cold radiator

To see if the thermostat has failed, completely cool the car, start it up, let it idle for about 3 minutes, feel both the upper and lower radiator hoses, are they very close to the same temperaute (if so, thermostat is stuck open) or is the upper rad hose hot while the lower is cool? (if so, thermo is shut, as normal)

[marioc89]

Ok. I'll check.

[marioc89]

Maybe the radiator is being overcooled - the grille isn't particularly restrictive, and not having the fan shroud by itself wouldn't cause a very noticeable issue, but the combination of the two plus cold weather might indeed cause the problem
You have an OBDII reader, right? What's the coolant temp at after 20 minutes of driving?

Well, I got the temperature. It was in the forties that moening and it was hanging around 114-116°. That evening, it was around the 70's and the temo was around 146 or somewhere around that.

[Towncivilian]

Do you remember approximately how long you were driving when it stayed around 146?

[marioc89]

For about an hour.

[Towncivilian]

It sounds like the thermostat is stuck open, then. I'd suggest an OEM thermostat as a replacement, I've heard too many horror stories about aftermarket ones.

Have you inspected the radiator cap according to this TSB?

[marioc89]

But with it stuck open, shouldn't it still get hot? Because it has to open anyway once it reaches normal temperature.

[NismoPick]

My 97 QX4 thermostat never opens during the winter ( read through my thread: 97-qx4-heat-comes-goes-sunload-sensor-t572498.html ). My temp gauge gets up to the middle, and using an infrared thermometer, the upper rad hose / thermostat housing gets to ~160*F... I believe I have a 190* thermostat. During the winter, the engine / fan / heater core can apparently keep the engine at that temp without the radiator.

In most any car, if the thermostat is stuck open or removed completely, the cooling system will not work properly because the water is flowing too fast through the engine / radiator. In some cars this will cause overheating because the coolant doesn't have time to heat transfer through the radiator, but with the cool-running VG33E, it will just suck out any available heat and never allow the engine to get to operating temp. This will also kill your mpg's because the engine is always cold.

[marioc89]

Oooooooh ok. Now this is the info that I needed. This may explain why this truck drinks gas like it's no tomorrow. And it makes sense now on why it doesn't heat that much. Exactly what I needed nismo. And thanks to everyone also contributed to this thread.

[marioc89]

But one more question out of curiosity. Why does a cold engine effect the mpg's in a car? Does it run lean or rich? If that's the case, what is the engine trying to compensate for or not?

[Towncivilian]

It does run rich when things are cold. The O2 sensors and catalytic converters need to heat up for proper operation, engine oil needs to come up to temp (as it is significantly thicker than optimal when cold), etc...

Page EC-27 of the factory service manual describes this in further detail.

[marioc89]

....and it's reading like it should. The old thermostat was damaged around the back end on the round groove part. But what I noticed for a truck like that, I stunned to find out that they don't use gaskets on those thermostat housing s. It sucks and it's sloppy.