I have a 1998 3500HD series 15k GVW with a 6.5 TD VIN “F”. I bought it knowing there were previous issues after I talked with a couple of mechanics who worked on it I figured it was a simple fix. They had no part in the sale, so I trusted them, they had told me that the truck started steaming coolant off but not in the oil. The customer was going to order a new truck anyways so it got parked then actually taken to the scrap yard. It had normal coolant issues so someone (not me or a real mechanic) replaced the heads, then things got really bad. Come to find out they used a van head on one side and a truck on the other side. The center bolts for the intake had been cut off and JB welded into the head. The truck never ran funny, it just had a little bit of smoke kind of dark grey. I had to get another set of heads and a new intake manifold and replace them again. After I replaced the heads and intake the truck ran great but it always used coolant, lots of it. I tried to find out what was causing the problem, I could never figure it out. I changed my oil about six times and not once was there any visible trace of antifreeze. One day about 4 months later I was driving down the highway and I heard a noise from the passenger side, I thought it was a rock coming off my tire. I drove about 50 more miles to a jobsite and when I got there I had found oil dripping. I cleaned off oil from around the intake it was quite a bit. I checked the oil and it was down a quart, so I added one and then drove home. I started really losing oil out the top of the engine but I didn't know it because it was raining really hard so there was no real smell or smoke. Then I got a big cloud of white smoke as I left a toll booth and the truck stopped. It would turn over but would not start. I had it towed to my house and then it started, but it poured white smoke out! It still has good power, idle, and oil pressure??? I have a ridiculous amount of time and money invested in this thing, it has a injection pump with 10k on it replaced in 2004. Any help would be appreciated. I am not a mechanic I just play one on TV. Thanks!

Welcome to the forum........

What was source for replaced heads?

Junkyard heads from a 95 6.5 TD then they were taken to a machine shop that the local Chevy dealership uses to be redone and sleeved. I was told that no matter what you do even new heads would tend to crack in the same spots as the old ones. Now I have heard that there are new heads and blocks that are not prone to cracking???

Most 6.5 heads are cracked between the valves, but cause no problem unless allowed to continually over-heat - is a repair kit for complete recovery.

A crack therein will get you coolant out the overflow and combustion detritus in the coolant - just the opposite of what you're seeing.

Cracked block can get you coolant in the crankcase or oil in the coolant, depending on location - oil pressure is greater than coolant system pressure in some areas, coolant pressure is greater in other areas.

A weak rad cap will lose coolant at an alarming rate, with no other problem.

Heater hose connections and rad hose connections can lose coolant at 15psi while you're driving, but seal off as pressure drops, so you get no puddles.

Water pump may do same.

Cracked plastic radiator header tank, or loose crimp thereon will leak at higher pressure, stop as pressure drops

Any coolant on the ground?

No coolant on the ground, but the PCV valve had the dexcool jelly, so we new it was internal, it just steamed off before really contaminating the oil. I need to send out an oil sample to know exactly how much was getting into the oil pan. We filled old clear plastic jugs with the old oil and let it sit for about a month with no visible contamination. The truck is down on the priority list because I actually had to remove the utility box and put it on another truck. I tried different pressure caps to see if I could make it better. No luck. During an average day of driving about 75 miles each way and some idling in between, it would use almost a gallon of fluid. There were no visible leaks and the water pump was repalced. The heads were repaired just as you described. I have heard that the blocks on pre 99 are weak and after the motors get the new heads installed the blocks are next to go. It was never overheated in my possesion, but who knows. The noise I thought was a rock could have been a piston?? I just do not understand how it can run so well and smoke so much!

Thanks

Source(s) for oil on the intake -

leaking valve covers

loose Injection Pump, around mounting flange - would also cause white Diesel odor vapors due to retarded injection timing.

turbo oil supply line, loose or ruptured

loose fittings at engine oil lines to cooler in radiator tank

OPS ruptured diaphragm

Source for white vapors with antifreeze odor -

heater hose connection at t-stat crossover, spewing coolant on turbo exhaust

same getting into intake would cause black smoke with nasty antifreeze odor, having passed thru combustion chamber

head(s) cracked in exhaust port area - would only leak at low Boost, as EBP is usually greater than coolant system pressure of 15psi - would see soot in coolant