Hi
Have a 94 suburban with a 96 454 vortex motor and 2500 trans in it. only done 65,000km
This always over heats when I tow my caravan (3.2ton) up hill.
Replaced radiator to an over size 3core
New water pump
New thermostat 68deg
Tested the heads
Trans mission cooler
But still cannot get further than 5km up hills before it cooks
Level driving is fine stays at 68deg
Can anyone help
Local mechanic is also baffled?

 

is it losing coolant? has the fan checked out? Have you replaced the thermostat to make sure it's not sticking?

if your not losing coolant and the fan is working as it should, and the thermostat checks out, you might consider a add on electric fan.

 

When going uphill are the rpm's going excessively high? Could the transmission be slipping causing the engine to work harder?

 

Greetings Patrick, welcome to the Forum.

Is that 68 you're referring to Celsius (154°F) ?
Possibly thermostat running coolant through radiator to fast or not opening fully.

Other thoughts would be...
Fuel Mix very lean,
Timing off,
Heater bypassed (hose loop)
Low frontal air flow, restricted air ram,
Fan not big enough. shroud missing...

 

Thank you for your ideas
Thermostat does work perfectly when we are not towing
Revs are low no transmission problems
Fan shroud is also on
Not losing any coolant. But does get pushed out into the overflow bottle
I will look into the lean fuel ? It does use very little fuel. Travelled the same distance in a F150 (to pick up the caravan because of the over heating) and it used almost double the fuel ( 5.4 l lariat )

 

That does sound suspicious, there shouldn't be that much difference. A 454 towing just over 6000 lbs should render about 10-14 mpg. Your Fuel Ratio should be about 12.5 to 14/1. That should be at your running/Hiway speed/RPM.

 

I would revisit this too, I believe the stock t-stat is 195f, if its opening too soon you could allowing the whole system to continually flush itself, meaning the coolant never stays in the radiator long enough to cool before its taken back into the engine....you could be running with a free flowing system effectively...