Cat 3116 potential issues and solutions

Hey All,

Still working thru initial diagnosis on my 1078.

One of the more troubling issues/symptoms is that the radiator cap is immediately pressurized (and venting) upon starting engine. There may be other causes (that I can't think of), but that tends to point to a failed headgasket (or more serious crack). I've been traveling and unable to dig into the truck further, so most of my effort has just been with google... I haven't been there to check if I have oil or chocolate milk.

It seems the head gasket replacement on this engine is less fun than many diesels due to the integrated injectors and the need to re-time them after replacement (with CAT specific tools). Also seems like a cracked head or block could be the cause of the failed gasket...

Soooo. armed with that insufficient information, I'm exploring options. (in all cases, I'd do the work myself)

1) fix it. if it is JUST the HG, then it's the easiest solution. Requires that I'm able to find and ID cracks if they exist (I have dye penetrate kit), and fab Cat style tools.

2) Cummins 6BTA (12v 5.9) swap. On the plus side, I have one from a school bus waiting in my yard, also it's about 400# lighter than the 3116 which would be a step in the right direction on the ridiculous weight imbalance on the 1078 axles. That said, it's arguably a little under powered for this truck... I'm not sure how well the tranny would play with the cummins, or if it would care or notice.

3) Cummins 6CTA (8.3) swap. I don't have one, and they appear to be a bit taller than the 3116. But a bit more powerful. Similar weight.

4) Cat 3116 swap/replace. Seems like price-wise could go either way with option 1 depending on my current engine's problem. And I'm still left with a CAT, which I'm admittedly less fond of than cummins.


Any thoughts?

I'm leaning a bit towards #2 as I've found the off road ability to be a bit pathetic compared to an M35. I think it's largely due to the poor balance. (yes lockers would also help). So I feel some hard work to figure out how to balance may be in order...


ciao
lino

I think turning assumptions into facts will be your first order of business. Once you have established what issue (if any) your engine has, you can go from there.

Is it a mil reman engine? I have seen alot of issues with those. Sometimes its worth the money to have cat diagnose it.

319 summed it up, you have too many unknowns... Pressurizing cooling system, are there any contaminants in the coolant? Is there any coolant in the fuel tank? This could be related to an injector cup/seal which might not be nearly as expensive to overcome...

As for the engine swap options, what are the peak RPM and peak torqe points on the cummins compared to the cat? The Allison programming is based on the Cats power delivery curve...

A closer axle weight balance would be desireable for a truck you are not planning on carrying 2.5T in regularly, but then you run into it now being over-sprung for the new lighter weight...

Ronmar said:

319 summed it up, you have too many unknowns... Pressurizing cooling system, are there any contaminants in the coolant? Is there any coolant in the fuel tank? This could be related to an injector cup/seal which might not be nearly as expensive to overcome...

Click to expand...

Ahh. I didn't realize the coolant and injectors came into contact. If there are contaminants in coolant, they are not visually detectable. It also smells like coolant (not diesel). I'll pull some fuel off the bottom of the tank this week to see if there's any coolant in there. And study up on the 3116 a bit more.

I did get out there today to check it out a little more. Oil looks like oil and at the expected, slightly low, level. Coolant had a large "burp" within 30 seconds of starting and vented off maybe 1/2 quart or more. I cannot get the coolant to remain at a level between the sight glasses. It's always venting it until level is much lower.

I hadn't gotten so far as to check torque curves of the various engine options. That said, I'd submit that the shift points in the 1078 with 3.9:1 pumpkins doesn't seem to be ideal anyway... But your point is a good one.

As to the weight distro and springs, you make another good point. In my case, it's much more likely I'd need the advantage of good balance off road without the payload, and if there's a load, much higher likelihood it would be on pavement. But, as you mention, it would still be too stiffly sprung.

Supraman, I'm not sure where to check if it's Mil reman. There is a tag on top of the engine that was a bit too gunky to read, but was hand written. Seems unlikely that was from CAT...


So this brings me back to asking for more advise...
Is there a way to diagnose the potential headgasket issue without pulling the head? I followed the troubleshoot guide in the TM (based on overpressure coolant), but it was not helpful. I'll dig into injector cup seals too.


Thanks for all the help!

You can do a positive pressure test on the cooling system to see if it’s leaking out anywhere. Most any shop can do a this.


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Handwritten tag could be mil reman. The reman facility will usually be pre printed on the label and the date and serial will be hand written. There may be a second label on the front of the motor also. The injectors sit in cups in the head there is a coolant path around the cups. Takes special cat tools to prep for/insert or remove the cups.

use blockchek on it. it is a chemical test that will positively detect combustion in cooling system. and it is cheap.