Isuzu NPS intercooler pipe problem and resolution.

clydeps

Member
The problem; Isuzu uses a plastic pipe on the output of the NPS's 4HK1 engine's intercooler, presumably because neither a flexible rubber pipe nor a pressed steel pipe as used in the intercooler inlet is conducive to mounting the manifold pressure sensor which is on the low pressure side of the intercooler.

However retaining a semi-rigid plastic pipe on the intercooler under pressure isn't easy. Isuzu uses a rubber sleeve inside the plastic pipe, clamped behind a rolled bead on the intercooler output tube. This retains the rubber sleeve well - but the plastic pipe has a tendency to slide off the rubber. This is what it looks like when it does:

IMG_20220223_202406.jpg

Notice that the end of the pipe is now distorted - this is probably why I'm told that when it blows off once, it will do so again. That's exactly what happened last week. It came off, we tilted the cab and reattached it, then about 30km later, on a freeway in rush hour, it came off again. Without any boost the engine is gutless - 40 km/h is about the top speed, and any kind of incline reduces it to around 10.

Coincidentally a couple of days before a business on the Gold Coast, CRG, that specialises in turbo manifolds had announced they were making fabricated alloy replacements for this pipe - I was pointed in their direction and ended up calling in to them on Monday. They told me they had sold their entire first batch and also needed to test-fit a variation of the pipe for the more recent (post 2018) trucks. They then suggested that since I had a single-cab truck right there that if I cared to let them test fit their prototype I could drive away with it fitted. So that's what happened and the result is below. So if anyone with an NPS is having the same issue get in touch with CRG - https://www.crgfab.com.au/ or find them on Facebook.

IMG_20220223_203749.jpg
 

Attachments

  • IMG_20220223_203749.jpg
    IMG_20220223_203749.jpg
    2.8 MB · Views: 4
  • IMG_20220223_202406.jpg
    IMG_20220223_202406.jpg
    400.6 KB · Views: 4
Before going the expensive route try aqua net hair spray. Even on rubber hose you sometimes get the pipes to blow off. Clean them up real good with rubbing alcohol, spray them down with Aqua Net and reassemble. It adds just enough stick that they won't blow off and are still easy to remove if needed.
 

Ultimark

Active member
That doesn't look good. Perhaps one could do a quick fix to get you going using some stretch self fusing silicone tape? That is amazing stuff, although there are limits.

Although there doesn't look like much room to get the tape around the OEM fitting, it may be possible. I'll tilt my cab tomorrow and check mine out. Mine's a February 2020 build, when was yours built?

Thanks for that, always looking to see where weak spots are. I presume that the same system is used in the NPR units as it's running the same engine, if so, does anyone know if it's an issue with them?

As for that hairspray, never heard of it. A quick search results in nothing in Australia; would generic hairspray be up to the task?
 

clydeps

Member
I'm sure any hairspray would work, it's just a kind of glue. As for rescue tape, I doubt it. I haven't been able to find out what the max boost pressure of the 4HK1 engine is but if it's 15 psi above ambient, with a cross sectional area of the tube of maybe 12 sq inches, you have something like 180lbs force trying to push the pipe off. I can't think of what you could do with rescue tape to hold that.

The issue is the plastic pipe end, clamped over rubber. Get a bit of oil in there (which is normal) and it gets slippery.

I assume the NPR has something similar, but I really don't know. CRG are specifically targetting NPS trucks. Mine is a 2021, but a similar pipe has been used for some years, it just changed a little in 2018 when the DPF was deleted.
 

SILRJW

New member
The problem; Isuzu uses a plastic pipe on the output of the NPS's 4HK1 engine's intercooler, presumably because neither a flexible rubber pipe nor a pressed steel pipe as used in the intercooler inlet is conducive to mounting the manifold pressure sensor which is on the low pressure side of the intercooler.

However retaining a semi-rigid plastic pipe on the intercooler under pressure isn't easy. Isuzu uses a rubber sleeve inside the plastic pipe, clamped behind a rolled bead on the intercooler output tube. This retains the rubber sleeve well - but the plastic pipe has a tendency to slide off the rubber. This is what it looks like when it does:

View attachment 708776

Notice that the end of the pipe is now distorted - this is probably why I'm told that when it blows off once, it will do so again. That's exactly what happened last week. It came off, we tilted the cab and reattached it, then about 30km later, on a freeway in rush hour, it came off again. Without any boost the engine is gutless - 40 km/h is about the top speed, and any kind of incline reduces it to around 10.

Coincidentally a couple of days before a business on the Gold Coast, CRG, that specialises in turbo manifolds had announced they were making fabricated alloy replacements for this pipe - I was pointed in their direction and ended up calling in to them on Monday. They told me they had sold their entire first batch and also needed to test-fit a variation of the pipe for the more recent (post 2018) trucks. They then suggested that since I had a single-cab truck right there that if I cared to let them test fit their prototype I could drive away with it fitted. So that's what happened and the result is below. So if anyone with an NPS is having the same issue get in touch with CRG - https://www.crgfab.com.au/ or find them on Facebook.

View attachment 708779
Thanks very much for the post above, the exact same problem happened to us 30 minutes after setting off on a long trip, on a highway with 110 KPH speed limit, truck has done 2000 K's. I called Isuzu and they knew straight away what the problem was and said I needed better clamps. After a 3 hour wait the hose was re fitted by Isuzu mechanic with better quality clamps, we decided to go home again and depart the next morning. Around 35 K's from where we had the first blow off the hose blew off again. We unpack the truck, tow truck takes our truck to dealership where they insisted that this was a rare case.They fitted the last original pipe available in Australia and assured me all would be well. They continued to assure me that ours was a rare event ?? I came home again this morning to find further information regards how many of these after market pipes are sold around Aus, it's a lot !! Have now decided to postpone the trip again and ditch the original pipe. I purchased the pipe from https://www.crgfab.com.au/ Don't need the worry of knowing the original could blow off at any time !!! Plan is to set off again next week. Again, thank you, the information was invaluable and prompted me to seek further info, none of which one will get from the dealership. Cheers.
 

clydeps

Member
I got a good tip about the clamps as well - use a little anti-sieze on the clamp threads when tightening up - this allows them to be done up further. Anti-sieze is a Good Idea on stainless steel threaded fasteners in general to prevent galling.
 
Last edited:

Forum statistics

Threads
186,790
Messages
2,888,064
Members
227,280
Latest member
Smithmds77
Top