Too cool?

white1500 · March 10, 2014

Back story: I swapped to a 34" radiator from a stock 28" last summer when I I had cooling issues. It did an awesome job all summer as expected in up to 120 degree weather.

Today: I went on a day trip and the engine temp went up to normal operating temp as usual. But on a 5 mile or so stretch that was all downhill with little to no throttle the temp gauge went down to a quarter of the gauge markings! I couldn't believe that I was down 20 degrees or so from normal, I was a little worried because I've never seen that before.

The ambient temp was in the 60's and with the larger rad is it possible that the engine was being over cooled? There's nothing wrong with that all but it was interesting to say the least. Has anyone seen that before?

After the downhill section the temp went back to normal for the rest of the day.

Bob D · March 10, 2014

.... with the larger rad is it possible that the engine was being over cooled?

I wouldn't think so if your t-stat is functioning properly

white1500 · March 10, 2014

A new thermostat was part of the cooling system overhaul from last July.

It included a new fan clutch, thermostat, 34" radiator, new hoses and obviously coolant. The water pump is a few years old.

I'm not worried at this point but it was very odd to see the gauge moving backward!

txab · March 10, 2014

I wouldn't think so if your t-stat is functioning properly

Agreed. If you have the proper temp t-stat and it's working properly then you should have no problems

kstruckcountry · March 10, 2014

I wouldn't really worry about it. On really long downhill sections I've had mine get down a ways. With 5 miles of 5% or so grade, it's going to happen.

white1500 · March 10, 2014

It was more like 6 or 7% grade. The engine must have been relieved to have a break after going up 4000 ft, but then it had to go back up to almost 5000ft after the huge decline.

And the 5.3 never skipped a beat or had trouble, I can't speak highly enough of my engine and gearing combo.

kstruckcountry · March 10, 2014

I have noticed that with a clutch fan vehicle it will be more noticeable. The 2004 Burb is cooler coming down passes than my e-fan 2006.

The 5.3 and 3.73's are great for climbing passes. I pull down to 3rd and punch tow haul on the way up so it will hold gear and pull, just leave it in for the ride down and the only time I need brakes are hairpins.

The motor is a lot happier spinning 3k constantly when climbing than gear hunting.

white1500 · March 11, 2014

For sure, 3k is a very meaty part of the rev range and it feels like a freight train.

And I honestly couldn't deal with anything less than the 3.73's, they just add so much to the overall package. She goes and goes when I ask her and I honestly can't complain!

kstruckcountry · March 11, 2014

Yeah and it's not like they cost you any fuel mileage either. Instead of shifting on the slightest hill it just pulls.

j-ten-ner · March 11, 2014

It was more like 6 or 7% grade. The engine must have been relieved to have a break after going up 4000 ft, but then it had to go back up to almost 5000ft after the huge decline.

And the 5.3 never skipped a beat or had trouble, I can't speak highly enough of my engine and gearing combo.

When you're coasting downhill and the engine hits a certain rpm it'll shut off the fuel supply.

You can actually feel it.

No fuel>no combustion>engine cools down. No matter how good your 'stat is.

Happened to me many times when I come back from Mount Seymour.

so long

j-ten-ner

white1500 · March 11, 2014

That's interesting, I can't imagine my old school engine being capable of that. lol

But it does explain the fact that it was just cooling down as if it was parked and shut off, especially with a gigantic volume of cold air being taken in at that speed every second.

j-ten-ner · March 11, 2014

That's interesting, I can't imagine my old school engine being capable of that. lol

But it does explain the fact that it was just cooling down as if it was parked and shut off, especially with a gigantic volume of cold air being taken in at that speed every second.

Oops.

Didn't realize we're talking about a 2000 model.

Sorry.

so long

j-ten-ner

oldmann · March 15, 2014

It was more like 6 or 7% grade. The engine must have been relieved to have a break after going up 4000 ft, but then it had to go back up to almost 5000ft after the huge decline.

And the 5.3 never skipped a beat or had trouble, I can't speak highly enough of my engine and gearing combo.

When you're coasting downhill and the engine hits a certain rpm it'll shut off the fuel supply.

You can actually feel it.

No fuel>no combustion>engine cools down. No matter how good your 'stat is.

Happened to me many times when I come back from Mount Seymour.

so long

j-ten-ner

No truck shuts the fuel off. Shuts of 4 cylinders maybe.

Sent from my DROID RAZR using Tapatalk

j-ten-ner · March 15, 2014

No truck shuts the fuel off. Shuts of 4 cylinders maybe. Sent from my DROID RAZR using Tapatalk

My previous '07 Sierra and my '13 Silverado both show in the DIC under "Instant Fuel Economy" that the engine is in V8 mode and the fuel consumption is "0".

When you watch the DIC closely while coasting downhill it'll show the V4 mode and the consumption around 2-3l/100km.

If the decline is steep enough the truck will go faster. At a certain rpm (I guess it is set by default) you can feel the engine starts "braking" a little more.

At the same time the engine goes back to the V8 mode and the consumption goes to 0l/100km.

When the truck slows down again and the engine goes under a certain rpm the fuel supply kicks back in again.

Decel fuel cut off is nothing new and I'd be really surprised if GM hasn't heard from it yet.

Maybe one of the specialists here can give some input.

Thanks.

so long

j-ten-ner

CapitalTruck · March 27, 2014

Let me tell you, I was going down some major pass (pulling a trailer) after climbing a long up grade in my 04. The temp gauge dropped like a rock. I think the issue was that it got nice and toasty on a long up grade. When I downshifted for the downgrade that fan clutch was still getting major heat off the radiator at first, so as the engine was turning fast (as I was going down the hill in 2nd) that radiator fan was also turning fast, and buddy it cooled off right quick. I had forgotten about this event...it kind of made me think twice also.