2nd Gen Non-Engine/Transmission Coolant By-Pass Hose Leaks During High RPM

[tomblue01]

She's been parked an hour. There are no spots on the ground. There's a smidgen of white residue by the #1 exhaust. There's an 8" x 4" wet spot on the black "felt" that insulates the hood above the by-pass hose. There's a small wet spot where the by-pass hose connects to the engine block. That's pretty much it.

Earlier: I tested her by maxing out my RPM's in 3rd gear after a 10 minute warm-up. I felt the governor kick in; 45mph [& nothing more!]; 2900 RPM [& nothing more!]. Okay, that was interesting. Made my way back. After parking, I went to check the temperature of various items in the engine bay using a cheap IR thermometer. Noticed the smell first. Saw the evidence second. [Upper hose: 158*]

Cooling system status: She's been flushed & filled. New 180* thermostat kit [has the two seals] by Gates; new by-pass hose; new short heater hose with the 90* bend; all from Geno's. Inside the cab, the coolant gauge didn't work until I replaced the actual sensor beneath cyl 6 on the driver side. Part made by Airtex; purchased from Rock Auto. [Expensive little bugger - $63 [other models use $6-$14 ones]] . Now the console gauge in the cab rises to about "220*" {the last white line before the red 230 mark} where it'll stay for just about a minute. Then it plunges down to 190*; slowly makes its way back up to 220*; rinse & repeat. I attribute the "higher" temps to the Airtex sensor, but that's why I had the IR thermometer.

Anyway, I'll have to compare temperatures later. I'll tighten the screw on the by-pass hose, and repeat the experiment tomorrow. I'm throwing this incident out here just to make sure all is well. I know from reading other posts that my console temp gauge reads very high for an unloaded truck. I welcome your thoughts on this matter.

 

[Bob4x4]

She's been parked an hour. There are no spots on the ground. There's a smidgen of white residue by the #1 exhaust. There's an 8" x 4" wet spot on the black "felt" that insulates the hood above the by-pass hose. There's a small wet spot where the by-pass hose connects to the engine block. That's pretty much it.

Earlier: I tested her by

maxing out my RPM's in 3rd gear after a 10 minute warm-up. I felt the governor kick in; 45mph [& nothing more!]; 2900 RPM [& nothing more!]. Okay, that was interesting. Made my way back. After parking, I went to check the temperature of various items in the engine bay using a cheap IR thermometer. Noticed the smell first. Saw the evidence second. [Upper hose: 158*]

Cooling system status: She's been flushed & filled. New 180* thermostat kit [has the two seals] by Gates; new by-pass hose; new short heater hose with the 90* bend; all from Geno's. Inside the cab, the coolant gauge didn't work until I replaced the actual sensor beneath cyl 6 on the driver side. Part made by Airtex; purchased from Rock Auto. [Expensive little bugger - $63 [other models use $6-$14 ones]] . Now the console gauge in the cab rises to about "220*" {the last white line before the red 230 mark} where it'll stay for just about a minute. Then it plunges down to 190*; slowly makes its way back up to 220*; rinse & repeat. I attribute the "higher" temps to the Airtex sensor, but that's why I had the IR thermometer.

Anyway, I'll have to compare temperatures later. I'll tighten the screw on the by-pass hose, and repeat the experiment tomorrow. I'm throwing this incident out here just to make sure all is well. I know from reading other posts that my console temp gauge reads very high for an unloaded truck. I welcome your thoughts on this matter.

Just a heads up the temp sensor is under $70 retail from Cummins

 

[GAmes]

The rise and fall of the gauge is normal. Newer trucks don't do it because the computer programming dampens it.

 

[tomblue01]

It's now as tight as the clamp design will allow me. It still leaks at max rpms, although less now. The hose clamps for that narrow by-pass hose are not "screw type". ...More things to buy at the store tomorrow!

Didn't have my thermometer with me today, so the temperature analysis gets bumped into the future!

 

[savage54]

tomblue01, are you talking about the small by-pass hoes? If so, I used injector hose clamps, which clamp the hose different than the stander stock or screw clamps.https://www.oreillyauto.com/detail/...mp-17485/fuel-injection-clamp/mp52f13/4459001

 

[tomblue01]

Right on, Savage! Thanks! $0.99 at my local O'Reillys. I forgot about getting new clamps once all my suspension components arrived. I looked under the hood tonight and saw a tiny green ring at the base of that hose. No puddles or spray marks were found, but then again I generally don't come anywhere close to max RPM.
I forgot about checking the thermostat with the IR thermo, too. A hasty measurement today ~ when my dashboard gauge read 190*, the IR thermo read 158*. Will need to take a few more measurements before I come to the conclusion that I want to blurt out right now...

 

[savage54]

Right on, Savage! Thanks! $0.99 at my local O'Reillys. I forgot about getting new clamps once all my suspension components arrived. I looked under the hood tonight and saw a tiny green ring at the base of that hose. No puddles or spray marks were found, but then again I generally don't come anywhere close to max RPM.
I forgot about checking the thermostat with the IR thermo, too. A hasty measurement today ~ when my dashboard gauge read 190*, the IR thermo read 158*. Will need to take a few more measurements before I come to the conclusion that I want to blurt out right now...

Just make sure you take the bypass hose with you or use one from the auto parts store to make sure you have the wright size clamp.I found out the hard way ,that the clamps come in different sizes .

 

[GAmes]

That isn't a coolant bypass hose, btw. It only bleeds air from the system when the engine is off. When the engine is running nothing flows through it, air or coolant, because the jiggle pin is seated in the engine side fitting. All explained in the FSM.

 

[savage54]

That isn't a coolant bypass hose, btw. It only bleeds air from the system when the engine is off. When the engine is running nothing flows through it, air or coolant, because the jiggle pin is seated in the engine side fitting. All explained in the FSM.

Hey GAmes, since its not a bypass hose, only bleeds air from the system when off. If it springs a leak, it won't show up until the engines off? Then it will leak or spry from the pressure in the system.When my dad owned the truck that little hose failed and sprayed coolant all over,so it must have some coolant in it. I know when I got a new one it was listed as a by pass hose, at the auto parts store.

 

[JR]

Is the nipple your clamping to made of copper? If the leak persists you may want to pull the hose off and inspect it for any corrosion or out of round. Shouldn't be any, but then again a new hose and clamp should seal.

I also don't think it's normal to be seeing 220 degrees off a 180 stat unless your still burping air from your system from the flush.

 

[NIsaacs]

That isn't a coolant bypass hose, btw. It only bleeds air from the system when the engine is off. When the engine is running nothing flows through it, air or coolant, because the jiggle pin is seated in the engine side fitting. All explained in the FSM.

What are you saying, Gary? When the thermostat is closed that little hose is flowing like mad. It has to, the water pump is pumping pressure at the head side of the hose. The heater core is also a bypass. If you installed a pipe plug in the thermostat housing side of the hose and installed a 3 foot hose on the head side and put that hose in a bucket, it would empty the head in just a few seconds. What am I missing here? Is the opening somehow sealed by the thermostat?

Nick

 

[GAmes]

The little hose is connected to a one way check valve (jiggle pin). It isn't a bypass hose in the common nature because nothing should be flowing through it while the engine is running. It makes no difference if the thermostat is open or closed. If it is working as designed coolant pressure holds the pin closed and nothing flows through the hose. When the pressure drops the pin opens and any air in the engine will bleed into the radiator. Quoting the FSM;

"5.9L Diesel Engine Only; The diesel engine is equipped with a one-way check valve
(jiggle pin). The check valve is used as a servicing feature and will vent air when the system is being filled. Water pressure (or flow) will hold the valve closed. Due to the use of this valve, the engine must not be operating when refilling the cooling system."

The hose will deteriorate and leak over time just like any other rubber hose. The last one I bought was $7 from Dodge. Cummins quickserve lists it as 3924755 Molded Hose. The check valve referred to in the FSM as a (jiggle pin) is 3926761.

 

[NIsaacs]

Thanks for the lesson, the older I get, I find, the less I know

Nick

 

[GAmes]

By owning and maintaining the same vehicle for over 20 years and 1.3 million miles a person gets to read the manual of lot more than most people do.