I will chime in here for a bit of input.

Lest say right off, I agree 100% with Maverick and More Power.

The Bypass gimick is just that, a GIMICK TO MAKE SOMEONE $$$$$$$$$$$$$$ and to try and fool people into believing that all is well.

The coolant flow through the 6.2/6.5 engines must work as it was designed in order to keep the engine cooling properly.

Head gaskets do go away on these engines, but usually its not until around 200K miles or so.

The gaskets used on the older 6.2 engines (80's) were of a different design than the ones used on the 6.5 later in the production sequence.

Currently the best gasket to use in a 6.2 is the late style 6.5 gaskets produced by Felpro.

One of the most overlooked items in the cooling system is the radiator, followed closely by the fan clutch.

The original equipment fan clutches were a POS. GM raised the temperature at which the clutch "Hooked UP" after the myriad of whinning complaints they had on the mid 80's pickups/Burbs/Blazers about FAN NOISE

I had a customer once that swore his tranny was slipping when he was in the mountains and pulling hard.

I checked the tranny and all was fine. He insisted that I rebuild the tranny, install a cooler, a shift kit and a special torque converter.

OOOOOOOK, so we did all that. Two weeks later the fellow came back, madder than a boiled owl, tranny was slipping again

Nope, that was not the case. I kept the rig for a weekend and took it over the mountains for a family outing.

As soon as the engine temp would reach about 200 (gauge) the fan would howl like crazy and the temps would drop right off

I took the rig back and explained the situation to the owner, he was not convinced so I installed a Tach in the vehicle and had him watch that.

Only after seeing that when the engine fan was howling, the RPM did not climb was he convinced.

I digress

Now GM was fed up with all the whiners, so they raised the temps at which the clutches engaged plus the fan designs were changed and the overall fan speed (clutch connection) was altered so the noise level was dropped off to a less noticeable level.

Soooooooo these are some of the reasons why the cooling issues have happened.

The radiators also are of concern, as the size and cooling capacity is marginal when new, and after 100K miles or more the cores tend to "SILT" in down in the areas that have a slower flow rate.

The cooling air passages also tend to plug up with Bugs, dirt and other crap that gets ignored.

The results are an engine that continually runs too hot.

The cooling system upgrade with the new HO water pump and dual stats is a great addition, but the radiator should be changed out too (high milers)

The other issue in the radiators is the crap that sticks to the inside of the cooling water tubes, this being deposits from minerals in "TAP" water used in the coolant mix.

These deposits through time and heat collect and insulate the coolant from the metal tubes, thus blocking the rejection of heat.

I have replaced radiators in 6.5 trucks that had heating issues and the problems go away, instantly.

The raiators looked fine, until you cut them open and took a good look inside.

A 6.5 rig with a fresh radiator, a good water pump and Stat/stats plus a fan that will hook up when the air coming through the radiator gets to about 210F, will cool just fine.

Now if your talking H1 Hummers, thats a horse of a totally different color.

The airflow through the radiator on these must pass such a torturous path that the rigs are prone to cooling issues.

The radiator mounting position is part of the problem, but we are not going to redesign the Hummer here.


Clean radiator, good fan clutch, upgraded water pump and dual stats and the thing will cool fine without the need for add on hoses, fittings and other such nonsense.

In fact, just a clean radiator and a good fan clutch and most rigs will do fine without the HO pump and dual stats.

Missy