R Model Heating Up

[MACKTRUCKS4]

A friend has a 79 R model 10 wheeler dump, with a 1984 300 2 valve with a tip-turbine. Lately it's bin running hot on hard pulls. Radiator looks good, changed thermostat, coolant looks good, and we put a gauge on the intake to see if there was a leak. Boost needle is steady up to 20 pounds but when it passes 20 going up to 25, the needle starts bouncing all over the gauge. Is this a sign that there is a leak? or should we look somewhere else? This truck never ran hot before. I first thought it was the gauge, but it is steady up to 20 pounds and after that , starts bouncing.

[HK Trucking]

Can you hear the engine fan coming on when it's hot?

If not, the viscous fan drive could be shot, causing the fan to be inoperative, resulting in overheating.

.

[Lmackattack]

belts tight? kink in hoses? if you turn the heater on does it blow hot? coolant level low? Head gasket issue?

regarding the boost gauge... When I first installed mine it seamed to hold steady at 25psi now it holds steady untill about 20 and then starts to flutter? dont know why it does this.. I taped my gauge into the top of the intake runner. my guess was the pulse of the gauge is caused when the vlaves are opening/closing near the tapped in boost gauge line. air is moving/stoping as the valves open and shut? I just dont know why it was fine before?

[Rob]

I'm with Herb on the fan clutch. There is a procedure to test that in the service manuals. It checks for proper operation by measuring temperature and percentage of slip. It is accurate and will show you when time to replace.

On your boost gauge giving inaccurate readings sounds like the turbocharger is shot. Instead of pushing the air out of itself and into the intake manifold the turbocharger is reaching a point of "saturation". This is the theoretical point where it cannot make any more pressure, nor overcome the resistance of the plumbing to shove the pressurized air into. Each time a discharge vane on the compressor wheel passes it's discharge point, the pressurized air already in the plumbing fights, or resists the discharge of the incoming air and this upsets the pressure balance in the intake system. This is the erratic operation of the gauge you are experiencing. Basically the turbocharger is needing rebuilt from my experience. Of course, if there is a boost pressure regulator valve that has malfunctioned, or a plugged charge air cooler, it can yield the same results. I have no idea what normal boost pressure is in that engine, or whether it incorporates a presure control device. Saturation if let go is fatal to turbocharger compressor vanes as the shock waves fracture them and then repairs get expensive.

Best check it out before going much further.

Rob

[rhasler]

So is the problem high coolant temperature or is it high pyrometer temperature? I'll see if I can find the specs. for boost tomorrow.

[MACKTRUCKS4]

Pyrometer peaks out at 1000 on the hardest pulls. I forgot to mention, the clutch fan was replaced and now you can hear the fan kick in around 195, but that did not help. The heater does blow hot. We checked for any leaks outside the head gaskets, none were found. No water in the oil. Belts are tight.

[bem14]

High coolant temp.

[Rob]

Have you guys blasted the radiator core clean? Sometimes they look clean but have a nice insulating layer of grime on the cooling tubes only a detergent will break.

Also when the truck is at an idle, (both low and high) look in the upper coolant tank for bubbles from a blown head gasket pressurizing the cooling system. This will impede coolant flow through the system allowing rapid heating.

Just another thought.

Rob

[Kav]

Hi everybody - If the radiator tubes are badly blocked , detergent cant always get down them so you have to unbolt the top tank and carefully push a dip stick down to the bottom tank. Another cause for overheating can be the impeller in the water pump breaking away from the hub, especially the early pressed stainless steel Mack impellers. Best regards - Michael.

[fjh]

Hi everybody - If the radiator tubes are badly blocked , detergent cant always get down them so you have to unbolt the top tank and carefully push a dip stick down to the bottom tank. Another cause for overheating can be the impeller in the water pump breaking away from the hub, especially the early pressed stainless steel Mack impellers. Best regards - Michael.

From what I have read here you need to pull the rad and a=have it disassembled and cleaned at a rad shop!But you should test the fan hub before jumping to that conclusion .use the card board in front of the rad trick that Herb mentioned, a 4 inch hole cut in it right in front of the thermal spring! you will be able to hear the pitch change if it is working properly.

[rhasler]

So is the problem high coolant temperature or is it high pyrometer temperature? I'll see if I can find the specs. for boost tomorrow.

My tune up specs for 1984 don't show an E6 300 engine with series charge air cooling. I'm guessing the original engine was replaced in 1984 and the engine components from the original were put on the ReMack engine. Judging by the other engines in the book I would guess boost should be between 19-27 psi

[MACKTRUCKS4]

We tested the anti-freeze for exhaust gases today and the test came back negative twice. Turbo has about 20,000 miles on it. The water pump was replaced about 50,000 miles ago. We will pull it off to check it. Does anyone know how much clearance should be between the impeller and the housing? Than if all else fails, we will pull the radiator out and have it cleaned.