The ol' Tahoe is down for the count - coolant in cylinder(s)

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Originally Posted by arveetek

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First, I made a bypass hose to make a circuit on the oil cooler ports:


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Casey

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I've spoken to a guy here recently who called to talk about why his 6.5 was losing oil pressure after warming up. It would be fine, then he'd lose almost all oil pressure... We talked about the possibilities I knew about on that first call.
On the second call I learned sorta accidentally that he had put plugs into the oil cooler line ports on the block. His original lines were leaking and he "didn't think they were necessary". I told him that if the oil cooler line circuit was to become blocked, it'll force a bypass valve to open. I continued by saying that I didn't know what the ultimate consequences would be, but an odd response in oil pressure would be expected...

Like you, I made a looped bypass when I primed the oiling system on Sarah's 6.5 while it was on the engine stand.
Jim

We had our first camping trip of the season this past weekend, and it was the first time I really had an opportunity to work the new engine pretty hard. Overall, I'm really pleased with the performance of the engine and upgraded turbo. I was a bit concerned the HX35 turbo might produce too much boost, but on long, somewhat steep grades with the transmission locked in 3rd and the engine at around 2500 rpm, the boost stayed steady between 10-12 psi with EGT's hitting a max of 1150*. The coolant temps were more stable than before as well; the old engine always ran hot, even with every 6.5L cooling upgrade available. I'm beginning to suspect the coolant passages may have been blocked with sediment. The new engine never even reached the halfway/210* mark. It would start to climb a bit, the engine fan would kick in, and then the temp would come back down to around 185*. This was with the A/C on and the ambient temp about 83*. Much better results than before.

All in all, even with just a stock build, the engine seems to have more power and pulls strong. There is a bit more turbo lag, though, as it blows a ton of black smoke until the engine can build up a bit more RPM and then the exhaust clears up and just keeps pulling. I can hit 15 psi in the upper RPM range at full throttle, so I do keep my eye on the boost gauge, but it doesn't get that high as easily as I thought it might.

An intercooler is next on my radar. I want to make sure this engine lives a long life.

Couple of pics of my rig below. 1995 Tahoe towing a 2017 Springdale 1800BH; trailer weighs approx. 4500 lbs and is 21' long; it's not a huge trailer, but is a pretty good load for a short-wheelbase 1/2 ton vehicle.

First pic is at Devil's Tower in Wyoming about 3 years ago; second pic is north of Mulberry Mountain in Arkansas:


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Casey

Great pics Casey! Looks and reads like fun!

So glad to hear that the little beast is gittenerdone......Makes all the work and rework all worth the effort.....

Enjoy.....

Way to go Casey!
Sounds like you did a great job!
d

After 4,000 miles, fuel mileage is still low. My best tank so far has returned 16.5 mpg, but the last two tanks returned 16.1 mpg. I'm a little disappointed, as I averaged a consistent 17 to 18 mpg with the old engine. But from the other posts I've read, 16 seems to be average. I'm not sure why the mileage would be lower, with a fresh overhaul and new injectors. Perhaps the engine could still use some more break-in time?

Casey

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Originally Posted by arveetek

We had our first camping trip of the season this past weekend, and it was the first time I really had an opportunity to work the new engine pretty hard. Overall, I'm really pleased with the performance of the engine and upgraded turbo. I was a bit concerned the HX35 turbo might produce too much boost, but on long, somewhat steep grades with the transmission locked in 3rd and the engine at around 2500 rpm, the boost stayed steady between 10-12 psi with EGT's hitting a max of 1150*. The coolant temps were more stable than before as well; the old engine always ran hot, even with every 6.5L cooling upgrade available. I'm beginning to suspect the coolant passages may have been blocked with sediment. The new engine never even reached the halfway/210* mark. It would start to climb a bit, the engine fan would kick in, and then the temp would come back down to around 185*. This was with the A/C on and the ambient temp about 83*. Much better results than before.

All in all, even with just a stock build, the engine seems to have more power and pulls strong. There is a bit more turbo lag, though, as it blows a ton of black smoke until the engine can build up a bit more RPM and then the exhaust clears up and just keeps pulling. I can hit 15 psi in the upper RPM range at full throttle, so I do keep my eye on the boost gauge, but it doesn't get that high as easily as I thought it might.

An intercooler is next on my radar. I want to make sure this engine lives a long life.

Couple of pics of my rig below. 1995 Tahoe towing a 2017 Springdale 1800BH; trailer weighs approx. 4500 lbs and is 21' long; it's not a huge trailer, but is a pretty good load for a short-wheelbase 1/2 ton vehicle.

First pic is at Devil's Tower in Wyoming about 3 years ago; second pic is north of Mulberry Mountain in Arkansas:


https://live.staticflickr.com/65535/...1a1a843a_h.jpg

https://live.staticflickr.com/65535/...3fe1494e_h.jpg


Casey

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Have you researched the made in China Hx35w? I’ve read that they spool faster and have less lag.

On my work bench is a good used Holset Hx35w and next to it is a made in China one. With my finger, I can spin the compressor wheel easier then the Holset. The Holset is lubed but the China one is not. Could be worth giving it a try on your build.

On an older build with both Holset and made in China Hx35w lubed the China one for sure had less resistance.

With my build, I set a strict rule for myself with regards to the Egts. Having the Egt probe on the square dimple of my exhaust manifold, I feel safe to assume that whatever reading I am getting on the pyro gauge, I increase 200 more degrees in my head. Internally, it will always be hotter then what the probe reads. So to be safe, 900 degrees is the max I will ever push it.

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Originally Posted by arveetek

After 4,000 miles, fuel mileage is still low. My best tank so far has returned 16.5 mpg, but the last two tanks returned 16.1 mpg. I'm a little disappointed, as I averaged a consistent 17 to 18 mpg with the old engine. But from the other posts I've read, 16 seems to be average. I'm not sure why the mileage would be lower, with a fresh overhaul and new injectors. Perhaps the engine could still use some more break-in time?

Casey

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That’s about what I am getting. I always push it hard.

My family and I just returned from a 13 day camping trip using the Ol' Tahoe to tow our 21' camper over 1100 miles.

Before we set off on our trip, I wanted to address the air filter situation. With the new HX35, the original air cleaner would not hook up, since the old turbo had a 3" inlet and the new turbo has a 4" inlet. I had temporarily installed a universal 4" filter right onto the turbo, but this was not a good situation since it was pulling in hot, under-hood air:


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I wanted to alleviate this problem before towing the camper up hills in near 100* temperatures. It finally dawned on me that I could simply cut out the opening of the original air filter housing to allow the larger 4" silicone hoses to fit inside. (Years ago I had swapped the 1995 flat-style filter for the 1997+ round filter housing.) So I had to order two new 90* 4" silicone hoses (since I had modified the first set to where I couldn't use them again), cut them down slightly, and bingo! The 4" K&N filter now tucks neatly inside the 1997 housing drawing air from the driver's side fender:


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The only draw back to this setup is now I can't hear the turbo as much! :( With the open element on the inlet of the turbo, the whistle was fantastic at nearly all speeds. Now, I can only hear the turbo when under load at pressures above 10 psi (which still sounds pretty sweet, though!).

With that, we set off on a 2 week trip to tour 5 different Missouri State parks. The trip would take us on a loop from our house in SW Missouri, heading east and stopping at 3 different parks that finally put us close to St. Louis before circling back west and ending up at Lake of the Ozarks. We encountered several hilly roads and some fairly steep grades. Here are the results of towing with the new engine:

Cooling - by far, the biggest improvement over the old engine is the cooling! Before, the old engine would always run hot, struggling to keep cool no matter what. I had every possible cooling upgrade on the old engine, but the temp would always climb on any incline or hard throttle input. I constantly had to keep one eye on the temp gauge. The fan clutch would usually stay engaged at all times, and the temp gauge would get dangerously close to the red line. It would never run cooler than 210* with the trailer on, usually hanging out closer to 220*.

Now, however, the temp never went above 210* (halfway on the gauge). In fact, it often ran around 190*, and the fan would kick on and off as needed, even with ambient temps in the upper 90's. (I have 180* thermostats.) It has never run this cool before. I wish I could identify why this is, but with a different engine block, different heads, different turbo, etc. there's no way to know which of these changes made the difference. I am starting to suspect the old engine may have had sediment filling up the cooling passages?

Boost - I was a bit concerned with having too much boost with the HX35, but unless I was pushing full throttle at high RPM (such as 2nd gear, 3000 RPM), it was not an issue. Most of the time, hard throttle in 3rd gear saw around 10 -13 psi. I saw a peak of 15 psi at high RPM situations, but rarely. I feel comfortable with those numbers, but would still like to have an intercooler to cool the charged air. The TurboMaster is backed nearly all the way off. EGT's on hard pulls were 1000 - 1150, with some short peaks of 1200 from time to time.

Power - Power is a bit better than the original engine. This is a stock rebuild 506, so the only power upgrades over the old 929 engine would be the diamond pre-cup HD heads, brand new injectors, and the HX35 turbo. My biggest issue is the 3.42 gears with 33" tires, so it's not built to be a towing machine. I had all the power I really needed for this size of trailer, but towing at highway speeds is an issue, since 4th gear lugs the engine too much, and 3rd limits my speed to about 65 mph to keep the RPM at 2500 or less.

Fuel economy - This is still a concern area. We had one long stretch of 4 lane highway that I pushed her hard to keep up with traffic (67 mph, 2600 rpm in 3rd), and that tank came back up at only 8.47 mpg!! I was shocked. After that, I backed the speed down closer to 62 mph, and used less of the cruise control. I noticed that with the cruise on, the ECM was often commanding a lot more fuel to keep up the speed, whereas if I just let it slow down a little on the hills, I would use much less fuel. After that, I averaged 10-11 mpg on the following tanks. Overall, after 1100 miles round trip, I averaged 11.7 mpg for the whole trip. I still think it should be better than that, but again, the 3.42 gears and 33" tires hurts the towing mileage for sure.

I had zero issues on the trip (other than my hood latch release handle broke for some reason... I must have hit it with my foot. Still works, though). I didn't have to make any repairs on the whole trip! Very strange for an RV trip! :D I am pleased with the overall performance of this 27 year old vehicle with 382K miles on the body, and am super happy with the lower engine temps. However, If I ever head back west towards the mountains again, I really need to consider a newer, more powerful tow vehicle. Today's modern roads with speed limits of 70mph + is just hard to manage with this kind of vehicle with a trailer on the back.

Some pics of trip:

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Casey

Sounds like a fantastic trip, Casey. Nice pics. No repairs is a huge bonus (better knock wood, quick).

Your gear ratio is too high (no surprise). Wrong gears, as you've seen, absolutely kills economy. I've run into this several times over the years when upsizing tires, and the only solutions have been either downsizing, or a re-gear. I just happen to have a complete 3.73 front diff from a 1995 GMC 1500. If it fits, and you take it up, you'll have to either swap your rear end or swap in the gears. It's just taking up space here, so it's yours for cheap + shipping. I'd even send just the R/P gears and, if you want. Check costs locally to see if you can beat it.

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Originally Posted by DmaxMaverick

Sounds like a fantastic trip, Casey. Nice pics. No repairs is a huge bonus (better knock wood, quick).

Your gear ratio is too high (no surprise). Wrong gears, as you've seen, absolutely kills economy. I've run into this several times over the years when upsizing tires, and the only solutions have been either downsizing, or a re-gear. I just happen to have a complete 3.73 front diff from a 1995 GMC 1500. If it fits, and you take it up, you'll have to either swap your rear end or swap in the gears. It's just taking up space here, so it's yours for cheap + shipping. I'd even send just the R/P gears and, if you want. Check costs locally to see if you can beat it.

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That's awesome, Greg, thanks! I've been wanting to swap gears for some time, but having to do both front and rear at the same time has held me back. I will check into that and let you know. Thanks!

Casey

I did something similar some decades ago with my 85. I upsized from the OEM 31" tires to 33" mudders (no lift needed). Economy and power was sapped. Re-gearing from 3.73 to 4.10 put it right back were it was before (including the speedo), with only a little loss of economy. I could have (and perhaps should have) added a turbo instead, but didn't. I never felt like I needed more power. I did the rear end first, mostly because it wouldn't cost me any more at the time, as I was already building a 12-bolt rear end to replace the twice-blown 10-bolt. I did the front end more than a year later.

Your giving me a bad case if hitch fever talking about your trip.
Tire size and gearing is critical. My 06 K3500 would look so much better with 285s but I would need to re gear to keep Duramax and Alison in the sweet spot. When I left California December of 14 I pulled a 36ft fith wheel to Carson City Nevada then on to Hurricane Utah, thru North end of Grand Canyon to Santa Fe NM. From there were came across to Knoxville TN. We had been living in the fifth wheel for 15 years and accumulated to much junk. I scaled it before leaving CA and was only 500 lbs below max for the truck.
Kept an eye on EGTs and let the truck do its thing. Sure was glad I had this truck and not my 94 K2500 it would have been to much for it even with the five speed. Managed to enhance millage on my trip by finding a semi to pace with and just slide in behind them. I could tell when I hit the sweet spot, boost would drop along with EGTs.
Yo have a sweet ride there I hope you enjoy it for a long time.

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Originally Posted by a5150nut

Your giving me a bad case of hitch fever talking about your trip.....

You have a sweet ride there I hope you enjoy it for a long time.

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Thanks!

Our family loves to travel, especially with the camper. I'm never ready to go home at the end of a trip. I am 46 years old, and the longest trip I have been on at one time is 3 weeks. Even at that, I still wasn't ready to go home. If it wasn't for that pesky job and needing to make an income, I would love to full time RV right now.

I've had this rig for for 17 years now, and I don't plan to let it go. My wife has mentioned more than once that we could sell it to get something newer, but I won't let it happen. It's just too unique. I often get comments at the fuel station and other spots... a lot of folks can't believe it's a factory diesel. My son would never forgive me if I were to ever sell it (he's 12 and loves it).

Casey

Casey,

Great story! Thank you for posting the pics and story.

Here's a quote from what was written about our 4.10 geared 6.5TD Project truck and towing a 27' travel trailer...

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Two thousand miles from our home in western Montana, we stop at a rest area in Indiana, on our way to Dayton, Ohio and The Diesel Page 2001 Rendezvous. This towing excursion added 4,500 miles to the odometer, and produced a 10.8 mpg average for the entire trip. While on the interstate highways, we tend to run at about 70-mph with a combined truck and trailer weight of more than 13,500-lbs.
https://www.thedieselpage.com/finale.htm

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I'm mentioning this here to help with expectations. Yes... a newer or more powerful truck could tow faster, but it really hurts the fuel economy, even with a new truck. I know from towing a 14' camper trailer with an NA 6.2L diesel how wind resistance affects towing. The power required to tow is logarithmic with speed. With my 6.2L NA, wind resistance created a barrier at 65-mph that could not be crossed.

These engines like to tow at about 2000-2400-rpm. Of course, your Holset changes things some, but the DS4 power delivery still likes that engine speed. I agree with others here about gearing, the 4.10's would help, but it's a little spendy to swap gearing. When I eventually turbo'ed my 6.2L 1982 GMC with a Banks Sidewinder (which had 3.42 gears and a TH700R4), I eventually settled into a routine while towing... If the tow situation was easy, I'd run in OD. If there was a headwind or slight incline, I'd run in 3rd, and speed was determined by where the engine seemed happy. I also tended to stay on secondary roads when possible just because it made for a more enjoyable trip.

Improved cooling.... the 1997+ cooling mods, a fan-clutch that engages when it should, and the Holset.

Thanks again for the pics!

I am contemplating a gear ratio change. The Tahoe came equipped from the factory with 3.42 gears and 30.5" tires. I upgraded to 32.8" tires years ago, and as a result, the engine has never been in the proper power band when towing.

I did some calculations for various gear ratios, and came up with the following info:


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Swapping to 3.73 gears would put me back to near factory settings. However, 4.10's would obviously gain more power. I'm just concerned 4.10's would not be the best for everyday driving.

On my old '81 C20 project truck with a 6.2L turbo diesel and 700R4, I ran 4.10 gears with 30.5 tires. The 700R4 had a steeper Overdrive ratio, though, so my cruising RPMs were still pretty decent. The truck delivered a consistent 18 mpg when empty, and had decent power when towing.

What would you do if you were in my shoes? Go with 3.73 to keep it close to factory gearing, or go for 4.10's to get the most power when towing. This is my daily driver, but we do tow our camper several times a year, and sometimes on some pretty long trips. I am obviously asking for the impossible, but would like to have both: the best MPG when empty and the most power when towing.

Casey

How is it currently for unloaded? How about the Gear Vendors as an underdrive for towing? Plus, you can call it an 8 speed...

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Originally Posted by JohnC

How is it currently for unloaded? How about the Gear Vendors as an underdrive for towing? Plus, you can call it an 8 speed...

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Just fine when unloaded, though the mileage seems a bit low. I don't want to spend the $ on a Gear Vendors, plus I don't think there's room for one any way. The driveshaft is really short as it is on this short wheelbase 4x4.

Casey

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Originally Posted by arveetek

I don't want to spend the $ on a Gear Vendors

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How does it compare to changing both ring and pinion sets? (Moot if it won't fit!)

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Originally Posted by JohnC

How does it compare to changing both ring and pinion sets? (Moot if it won't fit!)

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If I change gears, my plan would be to replace the entire rear axle; I would remove the current 10 bolt and go with a semi-float 14 bolt 6 lug. My local U-Pull yard sells complete axles for under $300. The trick will be finding the correct axle and gear ratio. Then I would just need to regear the front diff. Should be considerably less than a Gear Vendors.

Casey