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Old 02-09-2021, 01:08 AM   #1
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2004 Cat 3126 Known Issues?

OK guys and gals. I'm looking at a 2004 coach with a Cat 3126 engine. I am completely unfamiliar with this engine and am wondering about any known issues with this engine I need to watch out for. This is in a top of the line coach but I'm still going to have a very hard time selling my wife on a coach that old. The good thing it is will be about $50,000 less that what we have been looking at which will pay for some upgrades she would like (king bed and washer/dryer) and likely fix any issues discovered. Any and all advice will be appreciated.
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Old 02-09-2021, 06:28 AM   #2
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There is a hose on the heui pump that has been discussed quite a bit here, that would be worth reviewing. Also it should have had a valve adjustment done some time ago, and that should also be addressed if it is not documented. After those two, hoses, antifreeze, belts. These are good engines used in school busses, motor homes, boats, generators and on and on.

ETA Here is a link to the heui pump line. Good comments and a good read.
https://www.irv2.com/forums/f124/heu...ne-441428.html
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Old 02-09-2021, 06:36 AM   #3
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I have a 2006 Cat coach with 80,000 miles , and only minimal problems so far. For me, it's been a good engine.
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Old 02-09-2021, 07:46 AM   #4
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I have been a Cummins fan for ever. It was hard to to change horses and buy a rig with a 3126. It has been nothing but a very good experience. Ours is a 2005, those were the golden years for RVs. Now, they donít build them like the use to.
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Old 02-10-2021, 01:35 PM   #5
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Our 2000 has a 3126B, so not too different. Ours has 92k on it and we've put about 7-8k miles on it.

Our experience has been good on the whole. The biggest issues these engines are known for is related to the HEUI pump - failures and then also junk from the HEUI pump failing taking out injectors. From a practical perspective this happens but keep the oil and fuel clean and it should be fine. The HEUI hose is a known problem. I replaced it with the hard line (this is a Cat service bulletin). Some people have added a high pressure in-line filter between the HEUI pump and the injectors. There are kits available, Deboss Garage (see YouTube) did their own setup and that looks like that works too.

The more significant issue we had was low oil pressure. I always felt that the oil pressure was low on this engine, and while it was within spec it was on the very low end of spec even with 15W-40 (vs. the 10W-30 recommended by Cat). I replaced the oil pump and main and rod bearings and it's doing much better now. Now would I have ended up with a rod knock? I think yes, some might say no. But that was an issue. Cat did come out with a new style oil pump and I have no idea when that got put in. Here's my thread on this issue:

https://www.irv2.com/forums/f124/312...es-512024.html

Overall, I would say I'm very happy with this engine. I'd like more horsepower, but it's got very good torque.
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Old 02-10-2021, 08:40 PM   #6
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I have a 2001 3126E with about 60K I have not had any issues with my HEUI pump. I thought about doing some of the modifications but if you look at the number of engines in service and the number of failures, its not significant problem. There are different models of HEUI pumps and some are more reliable than others, i think the round top, like i have is the better version. You are best advised to use Cat filters and keep clean oil in it and you would be fine, like many of us have over the years. No issues with oil pressure or other problems so far. They are simple to work on, I did my own valve adjustment and use cat oil and filters. No issues. My only suggestion not specific to CAT is to calibrate your dip stick if it was not done by the prior owner. Otherwise its like another machine. Things wear over time.
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Old 02-10-2021, 10:04 PM   #7
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Quote:
Originally Posted by arcaguy View Post
OK guys and gals. I'm looking at a 2004 coach with a Cat 3126 engine. I am completely unfamiliar with this engine and am wondering about any known issues with this engine I need to watch out for. This is in a top of the line coach but I'm still going to have a very hard time selling my wife on a coach that old. The good thing it is will be about $50,000 less that what we have been looking at which will pay for some upgrades she would like (king bed and washer/dryer) and likely fix any issues discovered. Any and all advice will be appreciated.
Well arcaguy,
First, you're looking at an '04 with a Freightliner chassis I presume, correct? You don't say what make or model. For the 2004 model year, Freightliner was in a major changeover in many aspects of their chassis. I'm no expert on this but, our coach is an '04 Itasca Horizon 36GD with the CAT C-7 330HP. Our daughter and son-in-law just purchased an '04 Winnebago Journey 34H with a CAT 3126E. Our chassis build date is Oct of '03. They're chassis build date is, Oct of '03.

We have a Medallion Information Center LCD screen that displays various information on engine operations. Their coach does not have such an item. The diagnostic port in the rear of the coach, just above the radiator is a 9-pin, J-1939 Diagnostic port on ours. On theirs, it's a 6-pin, J-1587 diagnostic port.

Ours has a single fuel filter, theirs has two. Now, does all of this mean anything in particular, well, no not really. The 3126 pretty much the same engine as the C-7 with some differences. Both ours and theirs are the 330HP version with 860 ft.lbs. of torque.

So, just saying, there's differences in the 2004 production line so, are you dead sure that the unit you're looking at, has the 3126E or, the C-7? Just curious.
Scott
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Old 02-16-2021, 10:53 AM   #8
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Quote:
Originally Posted by Bigd9 View Post
I have a 2006 Cat coach with 80,000 miles , and only minimal problems so far. For me, it's been a good engine.
Quote:
Originally Posted by vseasport View Post
I have been a Cummins fan for ever. It was hard to to change horses and buy a rig with a 3126. It has been nothing but a very good experience. Ours is a 2005, those were the golden years for RVs. Now, they donít build them like the use to.
Hmmmm,
I'm a bit puzzled here. In all the years and tiny bit of investigation I've done, I was under the impression that, mid to late 2003 of Freightliner chassis production, that was the change over from the 3126 version of CAT, to the C-7 CAT engines. I know quite a few folks with '05, '06 and '07 coaches, with Freightliner chassis's, that have the C-7. They surely DO NOT have a 3126. Yet, Big D, while you don't actually say you have one, you're indicating you've had no troubles "with mine" which, I'm assuming you're referring to the OP's question about 3126 Engines.

veasport,
You state your coach is an '05, correct? Again, I was under the assumption from late '03 and into '04, that was the end of the 3126. Are you sure yours is a 3126? If so, learning stuff all the time.
Scott
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Old 02-16-2021, 02:12 PM   #9
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I own about a dozen 3126D/3126E and C7 Cat engines all 2006 and older. These are all in crane and bucket truck that get a fair amount of PTO hours and I have have to say we have had excellent performance overall with these engines. So good that we hunt down pre emissions trucks with these engines and rebuild the truck. Our average life exceeds 20,000 hours before we replace them. Based on information from Caterpillar every hour of run time equals approximately 43 miles. So I think for a relatively small engine pulling a lot of weight they do quite well. Most of these trucks at time of engine replacement have over 350,000 miles on them. My mechanic loves them. The key to a long engine life is maintenance. We change oil every 250 hours or at least shoot for that. We have looked into switching to synthetic oil but per Cat on these engines due to the high pressure injection pump there would be no benefit. Just repeating what we have been told by Cat.
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Old 02-17-2021, 04:55 AM   #10
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Good information Piros1, thanks. I didn't even know there was a 3126d, learn more every day.
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Old 02-21-2021, 11:50 AM   #11
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The Adept Ape U tube channel is a pretty good source for diesel engine information:
https://www.youtube.com/channel/UCxz...85PAb0uXWTlWPw
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Old 02-22-2021, 01:38 PM   #12
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I have Ď01 3126b, with 70,000 mi (Iíve put about 7k on in 3 years). My trips often include going round trip over (2) 4,000 ft mountain passes. Like Fire Up, have not done any mods and use Cat filters for fuel & oil and change oil at least annually. My Heui hose appears in good shape and no leakage. Freightliner told me my (old style) Heui is more durable than the newer style. So far, been good engine, have only replaced the plastic coolant reservoir and repainted the oil pan.

However, Iíve been told I have an exhaust manifold leak and is on my to do list. I think I may have bought it with a leak but still running well with up to 24 psi boost.

Diesel pushers are not Toyota Corrollas, so feel like to some extent we have to pay to play!
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Old 02-22-2021, 08:09 PM   #13
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However, Iíve been told I have an exhaust manifold leak and is on my to do list. I think I may have bought it with a leak but still running well with up to 24 psi boost.
Iívw seen advertisements for a ďhigh flowĒ exhaust manifold for the 3126/C7. If I were going to pull my old manifold off Iíd consider putting that back on. Similar for the turbo.
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Old 02-27-2021, 12:03 PM   #14
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I had to do exhaust manifold a couple years back.. We did it without removing the turbo, was a bit of a bear but got her done..
Quote:
Originally Posted by Seacrazy View Post
I have Ď01 3126b, with 70,000 mi (Iíve put about 7k on in 3 years). My trips often include going round trip over (2) 4,000 ft mountain passes. Like Fire Up, have not done any mods and use Cat filters for fuel & oil and change oil at least annually. My Heui hose appears in good shape and no leakage. Freightliner told me my (old style) Heui is more durable than the newer style. So far, been good engine, have only replaced the plastic coolant reservoir and repainted the oil pan.

However, Iíve been told I have an exhaust manifold leak and is on my to do list. I think I may have bought it with a leak but still running well with up to 24 psi boost.

Diesel pushers are not Toyota Corrollas, so feel like to some extent we have to pay to play!
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