Engine question for Weave

mikecop

Veteran Expediter
Charter Member
I have appreciated the mechanical info from Weave, and have printed some of his information for my files on my truck.

I have 334,000 miles on my FL70 with 3126 cat engine. A number of owners have told me that before I reach 400,000 miles this engine will blow, and that I should have a new head put on it soon to save money (versus complete rebuild or replacement when it blows). I was told that this could be done for about $1500.
I recently had new injectors installed. What is your opinion?

My 3126 is 230hp, which is weak for my current needs. I often haul near the max 33,000 GVW over the mountains of PA, WV, northwestern NJ, and northern NY. Should I run this engine til it blows and then replace it with a 300+hp engine?

I know you don't think much of either my 3126 cat engine or my 7 speed Spicer transmission.

I wrote this on the open forum rather than your direct email address because this way we all get the benefit of your knowledge. Thanks for your info.
 

Weave

Veteran Expediter
Charter Member
This is sort of hard to answer. Two guys I know who have trucks with 3126's both had to have the entire engine replaced at just over 400k miles, at a cost of around $13,000. Both of these engines had been very well maintained, but when torn down were found to have too many things worn and the labor plus parts costs to rebuild would have been more than the cost of a new engine. One of these cases in particuar I remember the camshaft and cam bearings were worn badly. The other one had something wrong with its block. So in these two instances replacing the cylinder head wouldn't have done them any good. Short of the injectors, I haven't heard of problems with the 3126's head. There must be some if others are telling you to replace it.
In theory you COULD replace the CAT with a Cummins ISC (the biggest engine that will fit into an FL70 with HP ratings up to 320) but the cost to buy one of these outright nonetheless the things that would have to me modified to retrofit it (exhaust, air and fuel lines, air conditioner, etc) would be too much. If you are going to hang on to your FL70, I guess the only thing practical to do is to save up for a new 3126, and run what you've got till its gone. Somebody told me synthetic oil helps these engines last a bit longer, maybe worth a try.
I haven't owned a 3126 myself (whew!) and have had really good luck with Cummins, even the disposable B5.9's. They only go about 400k too but are cheap to replace ($6800). The C8.3 and ISC Cummins are wet sleeved engines and are rebuidable on the frame. A full rebuild on my dad's C8.3 cost a bit over 7 grand with a brand new head and rebuilt turbo. I was looking at a new KW T300 with the ISC, and although nice the truck's cab seems too small for me.
I'm thinking of trying out an FL106 with the Detroit series 50 for my next ride. Somebody on this forum said they have ran this big 4 cylinder variant of the series 60 past 700k with no problems. I guess its only available in the FL106, which has a 4 inch taller hood than the FL70/80 to accomadate the engine's overhead cam design. It's teamed with the Eaton 9 speed roadranger.
Hope all this jabber helps out. At least I didn't get started on the 7 speed spicer again! It makes a real cool noise when 5th gear blows through the casing though :(
-Weave-
 

RichM

Veteran Expediter
Charter Member
I couldn!t agree with you more about the Cummins ISC,Today I rolled up 503,000 on this engine andf it still continues to perform well..I change oil at 9-10000 intervals and between changes use about 2-3 quarts. The engoine has never been touched,has original injectors ,rod bearings etc. I check my fluids daily and keep them topped off..The local Cummins dealer here (Cummins SE Power) has an excellent reputation and a very good service manager.He told me a complete overhaul would be betwwn $4-6 K depending on the turbo. He also suggested bringing it in at 500,000,dropping the pan and checking on the bearings. I am somewhat hesitant to do this as a oil analysis shows everything normal. What would you advise.
Also I have a Fuller 6 speed with original clutch and have had no problems. I change the Transmission fluid about every 50-60000
miles and it seems to have held up well,HOWEVER today I started to to hear a srange low pitched noise coming out of the Transmission area when the engine was lugging down in any gear below 1100 RPM or starting off in 1st. The noise goes away when the engine speed builds up to about 1200 rpm.I think it might be the clutch release bearing,any suggestions.?
I am sure that I speak for all of us in that we appreciate your advice..
 

RichM

Veteran Expediter
Charter Member
Well forget my query regarding transmission noise,turned out to be the a/c compressor spooling up.It!s giving a groaning sound at about 1000 rpm then goes away.Hope it stays away as I already put about $700 into it this year, new dryer and other misc items.The belt appears to be somewhat loose but is not squealing,who knows..
 

Weave

Veteran Expediter
Charter Member
The Eaton 6 speed is a decent little truck tranny- I have one in my D unit and short of the pin on the end of the lever wearing out every now and then its at 600k trouble free. I have replaced my clutch once. I'm glad to hear yours is ok.
My dad just replaced the A/C compressor on his C8.3. Sounds like yours is on its way out. Not too bad at $300 for a rebuilt one. The sticking point is recharging the system. Just trying to fire in R34 does no good-he had to take it into a place with a vacuum recharging system to suck the air out as the refrigerant was drawn in. Cost an extra $150 but worth it as his next call was a run into Florida!
At the point when my oil pan gasket starts leaking (its just a silicone bead on Cummins) I will drop the pan and plastigauge a couple of the main and rod bearings. Its just an indication of when I may need to rebuild, rather than wait till I hear the rods start knocking. Cheap and easy to do plus a nice new silicone bead. I'd get this done at 500k.
I've never had an oil analysis done. I change my oil so frequently I don't think anything would show up, but they seem worth the while especially for fleet owners who can't keep a watchful eye on every truck. Most folks who own and drive a single truck know it pretty well and know if its losing water or oil or making funny noises.
Take care and drive safe-
Weave
 
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