I have a 2003 Z71 Suburban 5.3l that I use to tow approx 5500lbs. It is a tough tow in NorCal from the Bay Area to Lake Tahoe. 2-3 very tough grades on Hwy 80 going from sea level to 7200ft over Donner Summit in 80-90deg weather in summer. Had a 2002 suburban for 16 years and towing the same boat on the same highway barely ever got hot at all. Hardly remember the gauge going past ~1 o'clock ish on the worst grades. On the toughest grades both the trucks are in second gear going approx 50-55mph at ~4000-4300 RPM.

Now I have the 2003 with an E-Fan, towing Cam, and cold air intake mods along with a tune from BlackBearPerformance and the damn thing is almost hitting the red (~250deg?) when going up the same grades in the Sierra's. I was hoping with the all the modifications, especially the towing cam from Summit Racing, it would help considerably, but it the power seems to be about the same and I have the heating issue I never had with my 2002 Suburban. Any ideas on why the darn thing is so close to overheating? The e-fans are working fine.

 

My experience with my truck:

1. I have a 160deg thermostat
2. Tune is configured to turn fans off at 55mph
3. Triple disc tow converter

I pulled about the same weight through Asheville in 2nd gear at 50mph on a 6% grade.

Trans never got to 200 and the engine ran about 195.

 

My 02 Tahoe 5.3 combo is below. I tow 7-7500 on occasion, usually about 5k. AC on, uphills, 5800' elevation, etc: never had a heat problem

185 t stat
2 row aftermarket rad
e fans off at 40
external trans cooler, with oe still in rad
oe engine oil cooler plumbed into aftermarket rad

212/218
4" intake
1 7/8 LTs routes thru 3.5" out the back
91 only tune

When I had my truck tuned, my tuner and I actually loaded his race car on the trailer and towed it around to dial in loaded timing values.

Aside from a coolant flush, new pump/t-stat and aftermarket rad: I'd say the temp is high from a lot of timing. May need to have that looked at in the tune. Bigger rad will help for sure. The oil cooler helps too, even tho it dumps heat into the coolant, it brought my truck down 10-12 degrees just with the addition of it

 

2003 is an old enough truck that the radiator might be plugged up. Also, the actual numbers that your gauges are reading might not be that much different. These gauges are not accurate. Mine always reads one or 1 1/2 marks below center, 12 o'clock in your terms. On mine, 1 o'clock would be very very very hot.
Since your tune is not stock, it is suspect. Maybe too much timing in the range that you are having the problem.

 

Thanks for the feedback guys. I am going to speak with the BlackBearPerformance about the tune and their experience with towing vehicles. From what I can gather they have done 100's of Chevy truck tunes if not 1000's over the years, so I am sure they can provide feedeback. The radiator is a quick fix item I might just swap out. I am going to do a compression test and coolant pressure test for ***** and giggles as well just to make sure there is no head gasket or other compression problem.

 

At least do the ICT rear coolant crossover. That’ll help with the rear cylinders/heat in that area. It’s like $35.

 

Interesting. Never heard of those before but have never really done a lot to these LS motors before until this year. I will check it out!

 

You'll be hard pressed to find a BB fan around here.

No matter who says what, or what flashy website someone has: a custom tune is always better. I bet your truck just has some canned calibration Justin thinks is a blanket for every stock truck out there and I bet it has like 10 degrees too much timing

 

Yeah, a custom tune is always better than a mail-in. More expensive, too but I think it is time I get on a local Dyno.

Anyone know of a good Tuner for Chevy trucks in the greater San Francisco Bay Area? Would love to get some tips from NorCal guys on who they use. Should I also post in the performance section as well?

 

Well, you hit the proverbial nail on the head. Had Nick at Newtech Performance in Hayward tune this beast on his Dyno today. Sure enough, timing from the BlackBear Performance mail in tune was in the range of 27deg advanced, I believe. They had set this towing suburban vehicle with slightly larger tires and a RV/Towing CAM up with a damn hot rod tune. It was pinging like a mother fuxxer. He backed the advance down about 9-10 degrees down to 18 or so. Nick couldn't believe I didn't blow a head gasket or worse towing up over Donner Summit with the way the tune was set up.

I do have 285 tires on the thing. This is not helping my towing capacity at all with the 3.73 gears. I will now be looking to upgrade to 4.10 gears to get more pep out of the hole and towing. They Dyno numbers actually went down about 5-10 ft lbs but if it stops it from pinging and gettting hot then the overall effect, apart from saving the motor, would be for the computer to not go into the power down mode when it senses pinging so the overall effect while towing might be having more power anyway!