New M998 Owner - White-Blue Smoke

I'm a new owner of a 1994 M998. Everything is excellent - no leaks, rust, etc. Problem is it smokes a bit at start. Looks like a bluish (oil?) but has a slight hint of white but mostly blue. I have seen youtube vids of trucks stressing in the mud exhibiting the same (if not worse) smoke in the same color but I can't find anything on whether this is normal or if there is somewhere I can start in terms of repair. It primarily does it when cold or when accelerating under load.

Any ideas?

Without images or a compression test it is hard to say.

Short of a compression test, you can also check the fuel delivery. Have you changed the fuel filters, bled water from the separator, bled the injectors? Smoke means something is affecting combustion, it's only a few things in the end. It is likely compression, but it could be something simpler too.
BDGR

No,it’s not “normal”. Blue smoke indicates excessive oil consumption. I wouldn’t worry about it. Just check your oil level often.

I appreciate the responses. I just got it back so this weekend I'll be replacing various maintenance items like what you listed above.

To further explain, the smoke only exists when cold and disappears when the engine is at operating temp (after fan cycles). After about 600 miles, there is no movement in the oil level.

Also, I noticed that upon cold start, the engine runs a bit rough (missing a beat every few seconds) and with each missed beat, a puff of smoke comes out. Again, this clears up after driving.

I plan on changing out glow plugs, filters, etc. soon. Thanks again for the responses!

Mine stutters a little too. I'm sure it's repairable, but my compression is low so the real repair is a powertrain swap. I see no reason to rebuild a 6.2 when better are available.
Keep us posted!
BDGR

Welcome to the group. In doing so... I would like to point you to the FREE manual that didn't come with your new rig.


The chapters are an easy read. Take a look at 3.5. I get this isn't your first rodeo too. Reading thur will "align the mine"

Like a doctor with a new patient. HumV coughing, sneezing and farting blue smoke could be concerning. Having some history is most helpful . Time for a full physical and being old might have to live with it for a while.

UUPppp.... Phone ringing. Got go, CAMO

Make it FUN, GOOD LUCK.

Milcommoguy said:

Welcome to the group. In doing so... I would like to point you to the FREE manual that didn't come with your new rig.

https://hummerhuren.files.wordpress.com/2013/01/hmmwv_test-diagnostics.pdf

The chapters are an easy read. Take a look at 3.5. I get this isn't your first rodeo too. Reading thur will "align the mine"

Like a doctor with a new patient. HumV coughing, sneezing and farting blue smoke could be concerning. Having some history is most helpful . Time for a full physical and being old might have to live with it for a while.

UUPppp.... Phone ringing. Got go, CAMO

Make it FUN, GOOD LUCK.

Click to expand...

Ahead of you buddy! I downloaded that on the way to pick up the truck!

I going to start with general maintenance, filters, new glow plugs (just ordered) and the thermo switch. See if that solves. My only comfort is that the symptom completely goes away when hot - atypical of leakage as the oil is less viscous at higher temps.

Thanks for the input!!

Sounds like you're going to have it under control. Thinking aloud here on the blue smoke thing. Not knowing ?? did you already change the oil?

For whatever the reasoning / science / product allegiance...what oil are you running?

Slipping and a sliding, CAMO

More often than not, you can have one or 2 bad glow plugs and the truck will start fine, actually, I’ve seen trucks start almost perfectly in warm wheather with just 4 good plugs, you must meter all 8 plugs to determine if you have even one bad plug, I had a 1097A2 that started almost perfectly till it got chilly, stuttered and a puff of white smoke, finally
after a year or 2 I checked all plugs...1 bad plug, changed it and it’s perfect In 25 degree temps.
cold advance should be checked too, I see a lot of them unplugged from the auctions due to GP in that area tearing out the fording CDR valve assys, that too needs to be metered, hot and cold to determine its serviceability

Thanks again all for the replies!

Ok, today was smoke city. I started it and it missed real bad and smoked vigorously - much worse than before. Bluish white smoke. I forced myself to deal with it just to see if it would clear and as soon as it was warm, it purred and the smoke cleared.

I ordered a new cold advance sensor and all new glow plugs along with an extraction tool. The cold advance sensor arrives tomorrow. We'll see what happens!

Milcommoguy said:

Sounds like you're going to have it under control. Thinking aloud here on the blue smoke thing. Not knowing ?? did you already change the oil?

For whatever the reasoning / science / product allegiance...what oil are you running?

Slipping and a sliding, CAMO

Click to expand...

I'm not sure what oil is in it. It is black (not what I'm used to fixing exotic cars), but the consistency feels good. In other words, no viscosity breakdown so I'm assuming it's recent.

What oil should I use? I can refer to the manuals but I figured enthusiasts with experience know best.

Edis06 said:

Thanks again all for the replies!

Ok, today was smoke city. I started it and it missed real bad and smoked vigorously - much worse than before. Bluish white smoke. I forced myself to deal with it just to see if it would clear and as soon as it was warm, it purred and the smoke cleared.

I ordered a new cold advance sensor and all new glow plugs along with an extraction tool. The cold advance sensor arrives tomorrow. We'll see what happens!

Click to expand...

your just wasting money if your not testing what you have...both tests take minutes to perform...

Retiredwarhorses said:

your just wasting money if your not testing what you have...both tests take minutes to perform...

Click to expand...

Actually, I'm replacing quite a few parts anyway. I'm in the process of repainting, new doors, top, all new decals, lights, 12 volt converter, etc, etc. The parts are cheap so, without any records, I'd rather just be safe with new parts than sorry. Hopefully, this will solve the problem.

If you have the ability, when you do your glow plugs pull the injector out and clean them up and pop test them. To see that they pop off at right pressure and they don't leak down ( drip ). If they drip or don't spray right, they will leak down over night and put excessive fuel in cylinder for the next start up cycle. Given you excessive cold smoke. Bluish white. The bluish in the mix could be just worn valve seals or wearing rings but if you're not use a ton of oil just keep a eye on it.

I tried to read all the replies but may have missed it, has anyone asked you if the wait light comes on for about 5-10 sec when the engine is cold?

Mogman said:

I tried to read all the replies but may have missed it, has anyone asked you if the wait light comes on for about 5-10 sec when the engine is cold?

Click to expand...

Yes, the wait light comes on when cold for about that amount of time. Flashes before a hot start, as expected.

Ok, I just had the cold advance sensor replaced. This WASN'T easy! It was fused. Had to soak in PB Blaster then use a blowtorch. New one is now installed. It seems to have helped but I'll know for sure when I start it in the garage.

Here's the only troubling result - of course, the coolant leaked out (at least 80% of it) and it looked like redish chocolate milk. The color of Alabama clay. Yes, it probably had the orange coolant in it, but that had some rust no doubt. So thursday, I am having the system throroughly flushed with a hose then the coolant replaced.

I also changed the oil and filter, using the Shell oil and Delco replacement filter. Again, the odd part was that a day after the oil was replaced, it turned black - without starting the truck! I replaced the oil and it was amber, then later on that day it already turned coal black without starting the truck once. That I suspect indicates lots of residual oil, so I plan on changing it again in the next few days.

Glow plugs are in, so I will be replacing these along with the PCV this weekend. I spent the last weekend repainting the entire truck in Rapco woodlands, and all the grills, bumpers, etc. in satin black. I also replaced all the hardware and all the lights, reflectors and side markers. Still have to replace the doors, interior insulation, gauges, windshields and gaskets. Fuel filler surround and a few other parts are on the way also.

I'll post pics soon. Again, thanks to you all for the help!