What Temperature Thermostat Should I Have?

grosss · January 3, 2009

Just had my coolant flushed because I don't know if the previous owner ever had it done and the existing coolant didn't look very healthy.

Part of the reason I did it is because the truck seems to take forever to warm up to temp. 1999 Silverado (99-02 BS) 4x4 with the 5.3L. I have a Scangauge hooked up and get a digital temp readout (sorry for the metric units!) before my operating temp would get up to around 90 degrees C (~190F) but now it barely makes it to 70C (~160F).

Did a search and couldn't find this info, what should the stock thermostat be, and what's the typical operating temperature range? It takes a good bit of driving to get anywhere close to the above operating temperatures...

Any tips would help!

GARB55 · January 4, 2009

Ok that's what I thought, I was pretty sure it was probably stuck open, but I don't know this engine that well yet, wasn't sure if maybe the cooling system was designed to keep the operating temp this low normally and I was just crazy!

Well you Might be Crazy However you do have a Temp issues and it sounds like a Thermostat!

C & A s Dad · January 4, 2009

Change the stat and go back with an OE type unit which will be 186 degrees. You will likely see an improvement in your MPG as well. The truck should be running 192 to 200 or so and anything less than this is going to have a negative affect on your MPG.

BuckFeverZ · January 3, 2009

Generally OEM thermostat is 190-210. You can get 160 degree thermostats, maybe thats what they put in when they did the flush.

txab · January 3, 2009

Rockauto shows 186F for stock. If you didn't change the stat at time of flush it's probably stuck open, or you don't have one. If they did change it then they may, as previously noted, put a lower temp model in. You can find your parts by going to www.rockauto.com or various other part sites

pennzoil29 · January 4, 2009

I have a 160 deg in my truck. After about 3 miles of driving it start's to cook me out of the cab. Of course, it's just an rc.

Zembonez · January 3, 2009

I think the GM T-stat is stamped 190 degrees. That doesn't mean all of them are but I'd bet that is the one you need. (or at least something in the 185-195 range)

grosss · January 3, 2009

I think the GM T-stat is stamped 190 degrees. That doesn't mean all of them are but I'd bet that is the one you need. (or at least something in the 185-195 range)

So is the fact that I can't get the temperature that high with fresh coolant after a good bit of driving a sign that the stat is stuck open, or is this the normal operating temp of the engine and it only gets high enough to open the stat under heavy load/hard driving?

(keeping in mind I'm in Toronto with the outdoor temps around 20-30F)

BuckFeverZ · January 3, 2009

No. It should reach normal operating temp no matter what type of driving your doing. I'm willing to be the t-stat is stuck open.

elcamino · January 4, 2009

If a colder thermostat is installed, the coolant may never get hot enough to trigger the appropriate control functions in the computer or TVS vacuum circuits. As a result the engine will run as if it were continually cold, which increases both fuel consumption and emissions. Too low an operating temperature also increases cylinder wear.

The coolant sensor on late model engines tells the computer when the engine has reached normal operating temperature. This, in turn, affects fuel enrichment, spark timing, operation of the EGR valve, purging of the charcoal canister, etc.

grosss · January 4, 2009

Ok so obviously the 5.3 has a bit of a different setup compared to the old 5.0L I'm used to... thermostat doesn't rest under a housing on top of the intake manifold anymore, it looks like it's suspended above the water pump via a rigid pipe? It's buried under the big plastic funny looking air intake hosing/box that looks like it's riveted to something else below that attaches to the fan shroud.

Is there a trick to taking the breather box stuff out of the way to get to it? from what I can tell I have to break the rivet to separate it from whatever that thing is below it.

Also is there a rad cap below the plastic cover that goes across the top of the rad/grille, or is the pressurized cap just the one on top of the overflow container?

grosss · January 4, 2009

Ignore my previous post, I managed to get the airbox hoses and such off, to reveal that the water pump hose goes directly into the top of the rad, and the thermostat is bolted to the engine on the lower rad hose, near the AC clutch.

Coolant on these engines runs in reverse of the previous gen? Logic suggests I need to drain the Rad to change this thermostat, correct? wont I need to flush the entire system of air then?

Zembonez · January 4, 2009

No. It should reach normal operating temp no matter what type of driving your doing. I'm willing to be the t-stat is stuck open.

I agree. It should reach operating temp. The thermostat keeps coolant circulating in the engine until it reaches operating temp. You might notice a drop in temp for a few minutes when the tstat opens initially but it should be quite brief.

grosss · January 4, 2009

Ok that's what I thought, I was pretty sure it was probably stuck open, but I don't know this engine that well yet, wasn't sure if maybe the cooling system was designed to keep the operating temp this low normally and I was just crazy!