Thermostat stuck open?

I have recently noticed that when it's cold - but not REALLY cold outside (<20F) that my truck is slow to warm up fully to center on the gauge. That isn't that unusual but - if it's fully warm and I coast down a long hill it will move to 1/4 on the scale or lower and that is pretty strange for a modern vehicle to over cool unless the t-stat isn't closing as it should. I would expect that if it was below 0F but high teens? Seems odd and will probably screw up the ECU's ideas about fueling and cold start open loop behavior.

SO... really my question is - is this normal - do you guys who live in a real winter also see this behavior or shall I schedule a visit to my friendly neighborhood Toyota dealer?

 

It's probably just fine. Ever since Toyota went to Aluminum blocks, I've noticed the same thing. Aluminum conducts heat much quicker than iron so it bleeds off heat to cold outside air quicker as well.

If I'm running the heater it acts like a second radiator and I lose engine heat at stoplights.

My 04 4Runner does the same thing. I was so concerned about it in the 4Runner that I replaced the thermostat because I was convinced it was stuck open. It wasn't and nothing changed with the new thermostat.

 

Well, that's good to hear. It's not causing any other symptoms so I'll just keep an eye to see if it's consistent and keep on as is.

 

Had a 2003 GMC that the thermostat stuck open on. It caused that particular vehicle to throw a code. If it's not giving a code I would think it is normal.

 

When that happens, stop and pop the hood. Feel the upper radiator hose (don't stick your hands in the fan) . If its hot, you have a stuck thermostat. If its just warm or cool, its working fine.

 

When you say "coasting", down a long hill... do you mean in neutral or with clutch in? Or in gear with your foot off the gas? I'm asking for a reason, because if I'm not mistaken this engine can do the fuel cut off routine under certain conditions.

EDIT: Yes, my truck takes a long time to warm up as well.

Frank

 

It's normal. Mine does it on days when its -6 and I'm driving around if I have the heater cranked up it is constant 180, and when I coast it will move down to around 160 until I get back on the gas where it heats back up.

Your heater, as stated earlier, is a second radiator that is a part of the cooling system, if it is running it has air blowing over it and cooling the engine down.

 

The other thing you'll notice in winter is that the heater O/P increases dramatically if you're into the throttle for any length of time. For example, if I've set it at 22C and am putting around town, it's nice and warm (consistent). Now when I give her the beans to get up on the highway, holy hannah it gets hot! Just sayin it's more noticeable in the Taco than other vehicles I've owned.

Frank