96LT1355Z28

iTrader: (2)

Hello everyone, I've been a member of LS1tech for awhile and read a lot here, but haven't posted much. I need some help/suggestions with my truck. I've owned it for several years (had 70K miles when I got it) it now has 220K. Its a NBS 2000 GMC Sierra 1500 ex cab Z71, 5.3, 4L60E, etc. pretty cookie cutter. My only mods are a homemade CAI with modified stock air box, Blackbear tune, larger external trans cooler, and a Flowmaster muffler.

For those who don't have time to read the whole here's what's new:
-E-fans and Clutch fan
-GM water pump
-GM T stat
-parts store temp sender

Here's the problem, I decided to install some F body electric fans before towing my Camaro to the NMCA/NMRA race in Joliet, IL this weekend. When Blackbear tuned my truck he set it up for the fans. So I pick up a harness and put the fans in. I notice city driving it's just fine but at highway speeds (55-up) the temp creeps up to 230-240 (normally is just under 210). I figure it's something to do with the fans and I'll mess with it when I get back from the race, clutch fan goes back on. Load up and get about an hour form home and I notice the coolant temp creepin up again. After stopping twice to check coolant level and let it cool I swallow my pride and turn around for home. Once home I install a GM water pump, and T stat. Put the electric fans back in and go for a drive, all seems good. Load back up and start for Joliet. Get abut 20 miles and temp is going up to 230. I stop at a parts store and install a new temp sender (DS head) just to make sure it's not a false temp. No change, now I'm sitting at home pissed for missing the race and I can't figure out what's going on with the cooling system. During all this the trans temp never went over 170.

I've been told the heads in 2000 are bad about getting pin holes in them causing a coolant loss. I have had to add coolant before the winter every year but it's never been more than just topping off the "overflow" tank maybe a quart. The under side of the valve covers have no sludge, surprisingly clean for the miles on the truck. The only other thing I can think of is a head gasket but why would installing electric fans cause it to reveal itself!

Sorry for the long read but since no one here knows me I wanted to give all the info I could, thanks for reading, a little help please!!

1FastBrick

iTrader: (17)

How about the year of the truck, what type of coolant did you use, How did yo mix it? what was the condition of the coolant before you did the work???

Have you spoken to the tuner to see if its possible he missed something???

Suburbazine

I could see it being the fans if it was happening at low speed and not highway speed. At highway speed the fans do very little in pulling air through the radiator as it gets rammed through at 55+MPH.

There is a good chance your radiator is full of sludge, have you purged it since you got the truck? The Dex-Cool that came with the truck new is known to crap out and turn to goo in the radiator, especially if you add anything NOT dex-cool to the tank.

96LT1355Z28

iTrader: (2)

Truck is a 2000, dexcool was flushed a year ago and filled with green coolant, about 40/60 more water. The coolant that came out when I did the water pump was clean light green in color. I sent an email to Blackbear and he said send the PCM to him so he can update the tune since one fan is on all the time.

I think I am gonna pull the radiator and have it cleaned next. I just don't understand why it would start overheating with the electric fan install and then continue when the clutch fan went back on a year after the switch from dexcool to green.

Thanks for the responses guys keep em commin!

whippled 8.1l build

have you varified that both fans turn on high when over a certain temp??
you could always put a toggle switch in line and manually turn them on..

when im towing with my truck on the highway i still halfto run with both fans on high at times.. i do have a 180 t-stat and highest temp i see is 205

96LT1355Z28

iTrader: (2)

Yes one fan is always on (PCM going back to Blackbear for updated tune) and the other comes on with AC compressor. I figured putting the clutch fan back and it not solving the problem eliminated the E-fans from being the problem.

Thanks for the responses, keep em commin. I'm looking for a shop to clean the radiator now.

iamkeniff

iTrader: (16)

Did you bleed the coolant system before taking it for a drive

96LT1355Z28

iTrader: (2)

Not after doing the water pump I didn't know it needed it. I put the coolant that came out when I did the water pump in a clear jug and noticed it had an orange hue to it, there was also sediment in the bottom of the drain pan. I'm guessing not all the dexcool got out when it was flushed and it gelled in the radiator. I ended up puttin in a new radiator, it was only $30 more than getting mine flushed. It seems to have fixed the issue but I need to hookup the trailer and put it under a load to make sure. Before installing the radiator I read my Haynes manual and saw there is a coolant bleeding procedure! Hopefully it's ok now!

Bad Scuba

This might seem like a stupid Question but I'm only askin cuz it happened to me!! Are the fans turning the right direction? I've installed god knows how many elec fans and never had a problem you know they always come with a black wire and the one of color blue, red or white whatever. Anyway I always hooked the color up to the pos + and the black to the ground. Well I was wrong that time the black was the + and the blue was ground. It also depends if ur pushing or pulling and if the fan is setup for both or just 1 way. Just a thought!! It's a quick check and boy did I feel stupid when I finally figured it out!!

96LT1355Z28

iTrader: (2)

Yes fans are going in the correct direction, thanks for asking though it's usually the simple and obvious stuff that gets overlooked!