Engine cools off while idling...?
 

It's been cold here, which may be a coincidence, but I thought I'd mention it. Hasn't been above freezing in days, or even out of the teens. It was zero last night.

Anyway, my truck was running for three hours straight this morning and never went over 170°. The crazy thing is that when I let it sit and idle, it cools off. If it idles for a half hour it goes from 170 to 140, or less, since that's where the gauge starts I don't know. It warms back up reasonably quick once I drive it a bit, but it usually runs warmer than 170 even when it's this cold out.

The upper radiator hose is hot, the lower one is cold. Radiator? Seems like it must be since that's what's in the middle, but I've never heard of a blocked radiator causing a vehicle to run colder. Just looking for some confirmation/other opinions before I spring for a new radiator.

Have you tried blocking off some of your grill or radiator with something to restrict air flow through it? Don't buy a radiator, sounds like its working fine, hot at the upper hose and cooler at the lower is whats supposed to happen, but if its 0 outside, imagine how cold that air is going through the radiator with the fan pulling. If your thermostat is stuck open it could cause this, but some cardboard on the radiator is free to try first.

My 94 did the same thing. They don't like the cold air.

This is my fifth winter with it, and while it certainly doesn't like the cold, it's never done this before. I suppose the thermostat is a cheap and easy place to start though.

ive got a brand new thermostat and a winterfront. and my truck will idle itself cold. my 1st gen did the same thing.

diesels like to be worked and they like heat so if your going to idle it for long periods of time you should look into a manual idle control to bring it up to 1000 rpm so your not washing the cylinder walls down and diluting the oil with diesel fuel.

I don't idle it much usually. That day was just colder than a witch's tit, and when I got to work it wasn't even warmed up yet even though it had been running over a half hour already. So, I left it running lest it start cooling down and lose what little heat I'd gained driving it in. As it turns out, it would have stayed warmer if I'd shut it off. I did end up sliding some cardboard in front of the radiator, blocking off most of the bottom. It hasn't made a huge difference, but enough that I know it did something. Still haven't tried the thermostat, but it's only a couple years old. Not that that matters, but I know it's not yet another original part waiting to fall off the skeleton when I whack it with a stick. All I can say so far is: thank heavens for heated seats.

I used to drive 35miles a day and at 50mph under 10F, it would never get over 170F. In fact, the thermostat never even opened. The heater core (since I had it on full blast) was taking all the excess heat it was making.

These things are some kind of crazy cold blooded.

Of course, that's probably why they can go a million miles, but I digress...

No it's just that they are so efficient at cooling themselves. But yes block off the rad completely is the main way to help them stay warm. Some other guys even remove the fan in winter to help maintain heat.