84 k30 Project

[KamperBob]

I recently got into an 84 Chevy k30 6.2 diesel. To my knowledge it hadn't been started since the mid 90s but it was garaged since then. I was shocked how it started on ~30 year old fuel but there are definitely some issues to sort out. The previous (not original) owner died and I'm dealing with his widow so history is limited.

1. When first started the oil pressure gauge starts increasing as expected but doesn't stop. The needle pegs high. There is also some old leak indications under the truck. I suspect some cause and effect there. Once I get a good service manual and workshop access I plan to drop the pan and check the pump. Someone on another forum suggested maybe there's a stuck relief valve. Seems plausible enough and changing dirty old oil can't hurt.

2. It has a turbo with ROTO-MASTER cast on the housing. Does that clue ring a bell with anyone? It also has a "Dyno-Tune" sticker on the air cleaner housing but that company seems to have disappeared ~25 years ago according to Uncle Google. He kept a paper file on the truck including the ad clipping how he found it which stated "new 6.2 turbo, trans. and transfer case." What exactly "new" really meant is anybody's guess. Could that turbo be a later 6.5 parts mod since factory 6.2 was NA only? What casting marks can I find to confirm which block is really under the hood?

3. The truck was stolen and recovered ~1 week later but some parts were stripped. The dash definitely has issues with lights and controls that need attention. Assuming the power train gets a clean bill of health that is...

4. I've read online that harmonic balancer rot was a problem with these 6.2 Detroit Diesels that if not fixed could cause web cracks and/or broken crankshaft. Hopefully a good service manual will walk me through that procedure. I also read that glow plugs were another problem area. Any other known issues to check out?

5. The truck was recovered with junker wheels. Before he died new mags and tires were sourced which I just installed. The wheels are not small at 33, 16.5 and 12.5 inches. I also don't have the right lug nuts yet but that seems solvable. The front wheels barely clear the fender corners when turning the steering wheel. In fact one rubbed slightly so I gently hammered a bit more clearance from maybe 1/4 to 3/8 inch. Not much I know but at least it can move under it's own power which delights me at this point. The truck already sits high so further lifting doesn't interest me. I'm hoping to carry a slide-in camper in the bed so the higher the less stable handling clearly. It'd be a shame to not use otherwise perfectly good wheels. So I'm curious what fender mods others have done for big tire clearance.

Looking forward to input from others. Thanks a bunch in advance!

[bd]

A few routine problems with the 6.2 include glow plug swelling and burnout due to excessive pulse width, injection pump elastomer ring disintegration, leaking head gaskets, fuel system air intrusion, cracked main webbing, and shattered pistons.  Rotating assembly damage often resulted from numbskulls using starting fluid.

The oil gauge symptoms could be caused by a faulty or incorrect sensor.  IMSM, 6.2 equipped vehicles used 80 PSI oil pressure sensors (OPS).  V8 gas powered engines typically used 60 PSI sensors.  All of the GM "gauge" OPS appeared indistinguishable save for the pressure calibration number stamped into the threaded hex nut at the base of the sensors.  If an incorrect sensor was installed at some point it would yield a false pressure indication.  A poor internal connection between the signal wire terminal and ground also can produce an open circuit that would peg the gauge high.

[Mr Diesel]

2. It has a turbo with ROTO-MASTER cast on the housing. Does that clue ring a bell with anyone? It also has a "Dyno-Tune" sticker on the air cleaner housing but that company seems to have disappeared ~25 years ago according to Uncle Google. He kept a paper file on the truck including the ad clipping how he found it which stated "new 6.2 turbo, trans. and transfer case." What exactly "new" really meant is anybody's guess. Could that turbo be a later 6.5 parts mod since factory 6.2 was NA only? What casting marks can I find to confirm which block is really under the hood?

4. I've read online that harmonic balancer rot was a problem with these 6.2 Detroit Diesels that if not fixed could cause web cracks and/or broken crankshaft.

The Rotomaster is some aftermarket concoction. Probably a 6.5 hodge podge of parts. It it works, keep it.

There is a theory that failed harmonic balancers caused broken cranks in these engines. I'm not convinced it is true, but it's fairly cheap insurance to just replace it. Not too hard either.

[KamperBob]

Thanks for the replies.

I need a good service manual. Any go-to favorites or recommendations?

[bd]

1984 Factory Service Manual

1984 Factory Wiring Manual

The 6.2 Liter Diesel Engine

Chevrolet Diesel Fuel Systems

[KamperBob]

1984 Factory Service Manual

1984 Factory Wiring Manual

The 6.2 Liter Diesel Engine

Chevrolet Diesel Fuel Systems

Wow, thanks so much!

[KamperBob]

#1 Follow up: the oil pressure sender is bad. I rigged a T splitter so both sensor and dial gauge got the same pressure, then varied using air from tool pressure outlet of compressor. Multimeter showed resistance. Lowest at zero pressure ~45 ohms. Resistance increased with pressure to 15-20 psi, then completely open circuit. Almost like it was for a low oil pressure warning light instead of needle gauge. I was delighted to see it had 30+ psi oil pressure so I didn't have to drop the pan and tear into the pump. I'm juggling other projects and priorities so it may be a couple weeks until I can move this one forward.

[KamperBob]

#1 Follow up: got new oil pressure sender installed today. Works good enough for now. Shows >30 psi at cold idle. Shop manual for 6.2 says 40-50 psi normal operating pressure at 2000 rpm and 80 max cold start. The gauge only goes to 60. Maybe previous owner put the dash back together with a gauge/cluster from a gasser. Shrug.

[bd]

If the oil gauge is 60 PSI, the pressure sensor should have 60 stamped into one of the flats of the 9/16" hex nut at its threaded end.

[KamperBob]

My guess is this 6.2 diesel had an 80 psi oil pressure gauge originally. From the widow I know the truck was stolen and recovered but some parts were missing. The previous owner may have used a gas-cluster oil gauge. She can't say. It was 30 years ago. Anyway, before installing the new sensor I bench tested it using shop air with adjustable tool pressure and a mechanical gauge for reference. My multimeter showed increased resistance with pressure up to 120 psi. So I'm thinking an 80 psi gauge might just plug and play...

[KamperBob]

Attaching a couple pix of clusters from eBay showing 60 psi gauge for gas truck and 80 psi for diesel.

[bd]

You're probably correct in your summation of an 80 PSI gauge in the original cluster.

FYI - The GM oil pressure gauges and senders are electrically identical.  All of the senders have the same 0-60 ohm resistance characteristics; gauges likewise are electrically and mechanically identical except for the face markings.  The differences between applications are in the spring rates of the senders and the face markings on the gauges.  In later years, many of the gauges had "Low" and "High" oil pressure scale marks in lieu of 0-60 PSI, 0-80 PSI, or 0-100 PSI.  This was done to minimize inventory since any of the three senders would work correctly with a generically marked Low-High gauge face.  If you inspect the sender stamping as previously discussed, you will know exactly which gauge suits the sender.  For example, I use a 100 PSI sender in my '87 R10 with 5.7L engine and a "Low-High" gauge face because it runs 90 PSI cold and 50 PSI at normal operating temperature.  If an unfamiliar driver didn't know it was a 100 PSI sender, the gauge indication would appear the same as any standard 60 PSI gauge.

The take-away here is to make sure the sender stamping matches the gauge markings.  So if you install an 80 PSI gauge, use a sender that is stamped 80 and you will be rewarded with an accurate reading.  The caveat, however, is that not all aftermarket senders are stamped per OEM protocols.  Shrug.

[KamperBob]

Thanks, Rich. I really appreciate your detailed knowledge of the gauges and senders. I'm actually good with mine as is since the dash and mechanical gauges(2) all agreed within a few percent using compressed air tool pressure to check calibration. It's really working!

PS- This is the sender I installed.
https://www.amazon.com/dp/B0080CHR3S

[KamperBob]

#1 follow up: the sender I replaced was stamped 80 on the base nut. So presumably its failure mode may've been the spring was shot resulting in open circuit and pegged needle.

[KamperBob]

More updates:

#3 dash progress is inching forward. The gauge cluster is mostly working now. New speedometer expected this week. Fan blows but vibrates so inspect/clean soon. Meanwhile, ducts sourced and reconstructed. Vacuum controls still need attention to select vents. AC will stay disconnected until that service makes my list. It's still cool in SoCal high desert so no hurry. Yet.

#5 wheels also progressing. I decided against 33" 16.5x12.5 wheels. Too big. Not enough front clearance. Got some deep dish Dodge rims that center nicely after 1.5" bolt on spacers. New stock size LT235/85-16 tires on order.

#6 issue is steering. Slop probably from blown boot on main link from the pitman arm. Hopefully tear into that this week.

It's exciting to see the old truck has good bones. Moreover, how serviceable it is, especially by an amateur mechanic.

PS- sorry; non diesel engine issues off topic for this channel...