Cooling System Performance in the GM 6.5 Diesel

Cooling system performance is greatly affected by the normal accumulation of dirt, bugs, weed seed and leaves. It is vitally important that the radiator and a/c condenser core be clean, spotlessly clean in order to do a good job of dumping coolant heat into the pass-through air stream.

The proper way to clean the radiator and a/c condenser cores is to remove the radiator from the truck. This looks like a bigger job than it really is.

When the radiator has been remove, you can more thoroughly clean its fin / tube areas.
We use a Foaming Cooling Coil Cleaner (Part #HDP1037) to help get all the crud out. The foam is sprayed onto the entire radiator core surface and allowed to ‘soak’ for about 10-minutes. Follow this with a pressurized water spray. A pressure washer can be used so long as care is taken to not bend the fins. A water hose and spray nozzle will work satisfactorily.

It may take several applications of the foaming cleaner / water spray process to get the core clean.

While the radiator is out of the truck, you can gain good access to the a/c condenser core for cleaning. Apply the foaming cleaner / water spray to the condenser core, just as was done with the radiator core. A great deal of debris will be concentrated in those areas just behind the engine oil and transmission oil coolers. These two coolers are constructed in a way, which allows the junk to move through them to lodge in the a/c condenser core. Often, the a/c core will be ‘matted’ solid with bugs and dirt.

When reassembling the radiator to the truck, always replace the upper and lower radiator hose clamps with the screw-type clamp. The factory spring-type clamp may not hold the hose onto the radiator because the clamp has taken a ‘set’ into the radiator hose and may not provide sufficient clamping force once removed.

Good airflow through the radiator is vitally important to maintaining coolant temperature during towing.

Another important factor in maintaining good cooling system performance has to do with the viscous fan drive that spins the cooling fan. The fan drive is designed to sense the temperature of the air that comes through the radiator. When the radiator is clean, the fan drive will begin to move the fan at or about 200*F water temperature and it will be fully engaged by approximately 210*F.

Many times, especially in the 1992-1996 model trucks and Suburban, this factory fan drive is commonly slow to react to the temperature increase, which allows the coolant temperature to rise far too high before the fan is engaged to cool things down again. Additionally, these factory fan drives do loose their ‘edge’ with the accumulation of miles and they become less effective at controlling fan speed and coolant temperature.

We offer the Severe-Duty Replacement Fan Drive for these models. This Severe-Duty fan drive is a direct, bolt on replacement for the factory fan drive and is used with the factory metal fan blade. This is a good way to go to assure proper cooling fan performance.

We also offer an upgrade fan and fan drive package for these vehicles. This is a 21” 9-Blade Composite Fan / Severe-Duty Fan Drive Package (Part #HDP1039) that provides superior airflow and it is quieter than the factory metal fan.

Additionally, we manufacture the Balance-Flow Cooling System Upgrade for the 1992-2000 GM 6.5 trucks and Suburban. This system is engineered to correct the poor coolant flow condition that exists in these engines. In their factory form, these engines suffer from a coolant flow condition that results in excessively high temperatures in the rear portions of the engine block and cylinder heads. These excessive temperatures create undue heat related stress in the block and cylinder head castings, which leads to cracking and premature failure. We recommend that the Balance-Flow system be combined with the 21” 9-Blade Composite Fan / Severe-Duty Fan Drive Package (Part #HDP1039) for peak cooling system performance.

We also recommend the use of one of the ‘water-wetter’ products available at most auto parts stores. These products are designed to make the coolant do a better job of absorbing heat from the engine castings and of transferring heat into the radiator. These products are available by a number of manufacturers and all seem to work well. Two manufacturers are Red-Line and Royal Purple, however there are a number of other brands available. These are most commonly packaged in 16 oz bottles and we usually use at least two of these 16 oz bottles per cooling system. They provide an extra margin of cooling.

If you have questions about these comments or about any of these products or any other Heath Diesel product, please feel free to contact us. Toll Free Phone 1 877 894 6266 or email sales@heathdiesel.com

- Bill Heath

Related Links:
Foaming Cooling Coil Cleaner (Part #HDP1037)
Severe Duty Fan Drives
21” 9-Blade Composite Fan / Severe-Duty Fan Drive Package (Part #HDP1039)
Balance-Flow Cooling System Upgrade for 1992-2000 GM 6.5 Trucks
GM 6.5 Diesel Parts

The PMD Isolator System & How It Works

The GM 6.5 PMD Isolator system for 1994-2000 GM 6.5 by Heath Diesel.

It is well understood that the PMD (pump mounted fuel solenoid driver) does not survive well as located in its factory location on the fuel injection pump.

In doing its job, the PMD creates considerable heat and requires a heat sink in order to dissipate that heat. The harder the engine is worked, the greater the level of heat generated by the PMD.

In theory, the DS-4 fuel injection pump was to function as a heat sink and mounting the PMD onto it was to provide a sufficient heat sink mass to absorb heat being generated by it. However, in practice, mounting the PMD onto the DS-4 fuel injection pump is not a practical solution as the DS-4 operates at a temperature ranging upwards of 180*F. As a result, the PMD cannot effectively dump enough of its own generation of heat and is forced to operate at very high temperatures.

Testing has shown that the PMD works best and lasts longest when its temperature is controlled to some point below 150*F and this is not possible when it is mounted onto the DS-4 injection pump. Temperatures anywhere inside the engine compartment are too high for the PMD, inhibiting its ability to function properly and shortening its service life.

The only proper solution is to mount the PMD complete outside the engine compartment, so that it can operate at safe temperature levels. The Heath Diesel PMD Isolator system is designed to remotely mount the PMD completely outside the engine compartment for premium performance and long service life.

The PMD Isolator system includes a new PMD module that features a ‘resurfaced’ mounting surface. It is joined to our Isolator plate with 4-mounting screws as well as an epoxy which provides a very high co-efficient of heat transfer. This method assures full and complete extraction of heat from the PMD. The result is improved fuel injection function and very long service life.

The Isolator plates are constructed of 6061 aluminum alloy. The plate is .300” thick and laser cut to exacting dimensions. The Isolator plate provides the heat-absorbing mass necessary to allow an effective transfer of heat from the PMD into the passing air. This allows the PMD to operate at approximately 7* over the ambient temperature, so that it stays very cool.

The PMD Isolator system is tethered to the engine by a special, 74”-long harness, allowing the unit to be mounted far away from the hot engine compartment.

The 4-wd version mounts the PMD Isolator plate onto the forward surface of the front skid plate, just below the radiator, behind the license plate assembly. When assembled to the skid plate, the PMD module is housed behind the Isolator plate and between it and the skid plate. It is impervious to weather and not subject to road hazard.

The 2-wd version uses an Isolator plate that is configured differently than that of the 4-wd. This plate mounts to the upper surface of the lower flange of the front bumper, utilizing two of the existing holes in that bumper flange. It extends straight back from its mounting.

While longevity is the goal in the PMD Isolator design, they do provide a slight gain in power (5-6hp) over that provided by any of the higher temperature, under hood locations. The PMD Isolator system is warranted for 7-years with a free replacement part warranty. Many have been in continual service for more than 11-years. Solves the problems associated with the PMD---once and for all.

Questions about this or any Heath Diesel product? Feel free to contact us anytime 1-877 894 6266 or sales@heathdiesel.com

- Bill Heath

Related Links:
PMD Isolator Systems for Chevy/GMC 6.5
2-wd PMD Isolator System
4-wd PMD Isolator System
GM 6.5 Diesel Parts