5.3 Lower Rad Hose Ice Cold

[Digger3]

I have a 2000 NBS 5.3L. The heat output from the heater was not very good, & the lower rad hose was ice cold. Flushed & backflushed the heater core (didn't notice anything abnormal getting flushed out), & installed new GM t/stat. Now the heater is putting out great heat, temp gauge reads normal, but the lower rad hose is still ice cold.

 

Removed upper & lower rad hoses, & ran water into the rad inlet, & observed good flow coming out of the rad outlet. All of the hoses get hot, with the exception of the lower rad. If you squeeze the lower rad hose & increase engine RPM's, the hose gets firm, so I'm ruling out a bad pump, or plugged rad. The right rad tank is warm at the top, & gets progressively cooler as you run your hand to the bottom.

 

I noticed when I removed the surge tank cap, that there was no hissing from pressure build up. Is the cap at fault?

 

What's the chance I have an air lock in the lower rad hose? Does anyone think I need to replace the rad?

 

I'm wondering if the t/stat I bought is bad, & is stuck closed? Although, if the t/stat was stuck closed, wouldn't the truck overheat?

 

If anyone has some suggestions, I would sure appreciate it.

[asilverblazer]

Sounds like the radiator is doing its job to me.

[txab]

Sounds like the radiator is doing its job to me.

+1

[ken1mod]

The lower rad hose handles water cooled by the rad. In really cold weather, it will be quite cool. Normal Top hose should be constat thermostat temp.

 

ken

[Digger3]

Shouldn't the lower rad hose be at least warm to the touch? We've only seen below freezing temperatures a couple days so far. Last night the temperature was 50F once I hooked the hoses back up, & refilled. The fan pulls a ton of air through the rad, but is it going to remove that much heat from the coolant?

 

How important is it to go by GM's recommendations for draining & refilling the coolant, & rev the engine to 3000RPM in 30 second intervals until the t/stat opens? This is the first vehicle I've owned that doesn't have the rad cap on the rad.

[txab]

I just changed mine and did no revving. Just let it warm up at idle, then test drove it. Let it cool and check the level again. No, I never checked the temp of my lower hose. If you put thermostat in correctly and you put in a 186 degree stat. Everything should be fine. Maybe you're not driving it far enough to really heat up Y

 

If you're concerned, put a new cap on the system

[Digger3]

That's exactly what I did too Darral. It's impossible to put the thermostat in upside down since they're now integral with the housing.

 

Maybe I'm chasin' something that's not broke?? It just seems wrong not have any heat at the hose.

 

I'm going to definately grab a new cap today.

 

Thanks for the help & sugestions fellas!!!

[txab]

Not all 'stats are integrated into the hose housing. Many places sell them that way. I just replaced mine with a Stant 'stat. Guy at the parts store wanted to sell me the type you have since it was almost 2x the price. I just put a regular one back in. I just have to think you're just not getting hot enough due to ambient air conditions. As long as you're getting heat from the heater pretty quick that should rule out an open 'stat.

 

As you filled the system did you have the upper radiator hose loose so that air could escape? If not that hose, maybe the one that runs from near the top of the rad. to the plastic tank. Either one will allow trapped air to escape.

[Flyingbrian]

new cap should solve your problems seen it before

[Digger3]

Well, I put a new cap on last Friday, & now I have system pressure, which will raise the boiling point of the coolant. The lower rad hose is still ice cold. I think I'll look at the replacing the rad when time permits. I'm not too worried right now since I'm not overheating.

[chuck16]

This is the first vehicle I've owned that the TStat is not up on top of the engine but, in the Water Pump. Or at least that's where I remember it. Remember how big your Rad is and how much coolant flows through it.

 

When I replaced my Water Pump I too noticed how cold the bottom pipe was. The top one was hot but, cool in the bottom. The Engine runs just left of Center as far as temp is concerned and the Rad fan comes on when she really get's hot.

 

Sounds like your engine is running fine to me...