Over the last 6 months or so my rig takes forever to warm up. I let it idle for 5 minutes then take off, it takes 5 miles or more to reach 190 on my scanner. I can feel warm coolant circulating within 2 minutes, indicating a possible stuck open thermostat(s). Its at the dealer now, and they just called and said its normal, all diesels take forever to warm up. Well this one used to hit 190 in less than 5 miles, no matter what the oat was. Has anyone seen an LLY thermo stick open?

Mine takes 3 or 4 miles to warm up. It makes no difference how long I let it idle for either, can be 1 minute or 15 mins it never reaches normal temp till I get on the freeway, which is about 4 miles from home. Just go easy on it till it gets warm. The only thing I could think of is... Did you notice the slow warm ups about the same time you removed your CAT ? The less back pressure will allow that hot air to escape faster, thereby reducing the engine temperature ever so slightly but it may cause a slower warm up. Maybe....

True Rob

In mild weather, the truck is overcooled at idle. You could speed it up by putting it in gear with the parking brake on, but that is not smart IMO.

It sounds normal. Did something change recently? Just curious. :)

Hey guys,


No changes were done lately. Today I monitered the ect on my scanner, felt a slight warming on upper hose when ect was at 114 degrees. It took 9 miles of driving to reach 180 ect. Traveled from Oceanside to Long Beach today, wife driving, scanner in my lap, average ect was 185 at 70 mph, oat was 58-65 degrees. I dunnao, maybe i'm crazy and its ok. I will pull the stat cover and just look at them.

One good thing, I saw the best mpg yet...23.4 going steady 65-70 mph with cruise on. I just installed 4 new Michelin LTX-MS 265-75-16's (stock size on a SRW 3500) and I think those helped the mpg.

Wouldn't trust that mileage figure unless I hand calculated it...

Wouldn't trust that mileage figure unless I hand calculated it...


Yeah, your right, the dic can be off. But in the past, the hand calc was darn close to the dic. It averages about 14-16 around town and about 19-21 hiway. Towing about 7-9.

Mine takes forever to warm up unless I've got a load strapped to her back. But I have a few OH mods that might affect it!

I have a 2005 lly I drive 9 miles to work and it does not reach operating temp in that time even with the winter front on. My dealer is a looser they say that it is normal so I pulled the housing and the front thermostat has two bleed holes about 3/16 inch each I think gm puts these here to facilate faster fill of the cooling system at time of assembly. They pass too much coolant and the engine cant warm up fast enough.

But there are 2 floating balls plugging those holes, correct????

Mine takes forever to warm up unless I've got a load strapped to her back. But I have a few OH mods that affect it!

All your "overheat mods" have nothing to do with warm up because you guys keep forgetting you have these gadgets called "thermostats" in your trucks, so that when you are warming up, there is no coolant flow and your "overheat mods" have nothing to work on. You could replace the radiator with a piece of hose and the truck would warm up the same.

Over the last 6 months or so my rig takes forever to warm up. I let it idle for 5 minutes then take off, it takes 5 miles or more to reach 190 on my scanner. I can feel warm coolant circulating within 2 minutes, indicating a possible stuck open thermostat(s). Its at the dealer now, and they just called and said its normal, all diesels take forever to warm up. Well this one used to hit 190 in less than 5 miles, no matter what the oat was. Has anyone seen an LLY thermo stick open?

First, accurately measure the time of warmup. Use a watch and the reading from your scanner, measure time from 100* to 180*.

Then take hose pinch pliers and completely pinch off the upper hose. Then measure the time again from 100* to 180* under the same conditions.

If there is a big difference between the two times then you have flow going on, as in if it is much slower to warm up with the hose pinched.

Easiest way I know of to check for a stat that isn't closing. :) I have pulled mine on my truck and found a piece of gasket material holding one open so it can happen.

Good luck!

.

The dash gauge makes it look worse than it is.

Reading the actual engine ECT from the ECU (somehow) will show about 180-185F. Normal = about 192-196.