2010 Hino 258 Flatbed overheat when Idle Raised

likemlow · Nov 1, 2017

Hi all! Our 2010 258 is overheating only when the driver has the idle raised with the control knob. It happens pretty quickly, he claims that starts within minutes. He uses the Idle up while operating the PTO. When the truck regenerates, it raises the Idle up to about the same rpm and the truck overheats then too. We've Replaced the Fan clutch, Blew out, Drained and Refilled the radiator. Other than those exact instances it will always run cool at idle and driving down the road. Thanks for any input!

greasytshirt · Nov 2, 2017

I would have a combustion gas test performed on the cooling system. If the head gasket is blown, it will put bubbles into the cooling system that can disrupt coolant flow.

Also, I'd consider having either the pto controls wired into the ECU (and have an appropriate rpm programmed in), or have the cruise control switches programmed to do the same thing. The idle knob was not meant for this, as the 980 rpm is barely adequate for PTO work.

Oh, one other thing! Is the exhaust brake coming on with the idle turned up? If so shut it off. Having the exhaust brake on with the pto on will more than double the fuel used , and can cause overheat if it's out of adjustment.

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likemlow · Nov 2, 2017

Thanks for the input. The driver says he leaves the exhaust brake on all the time. I told him to keep it off and see if anything changes. I also told him to try the cruise control for the idle increase instead of the knob and he said it works. Kinda funny cause he's had that truck for a few years now and never tried it. I also thought it was either/or depending on the years. So what is the purpose of the knob then if not for a pto?

greasytshirt · Nov 3, 2017

likemlow said:
Thanks for the input. The driver says he leaves the exhaust brake on all the time. I told him to keep it off and see if anything changes. I also told him to try the cruise control for the idle increase instead of the knob and he said it works. Kinda funny cause he's had that truck for a few years now and never tried it. I also thought it was either/or depending on the years. So what is the purpose of the knob then if not for a pto?

The computers in these things are actually very customizable. You can have stuff like 2-speed pto settings, remote panel start control, the ability to actively regen while stationary and the pto on, all kinds of stuff. The cruise switch can be programmed to immediately jump to a specific rpm, or slowly ramp up.

The idle knob is mostly a remenant of earlier Japanese trucks. You can turn up the idle speed and turn the exhaust brake on and it'll force the engine to warm up faster. That's basically it. I think in 2015 the knob was removed entirely. The trucks are coming from the body builders with pto controls already tapped into the computer.

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likemlow · Nov 14, 2017

greasytshirt said:
Oh, one other thing! Is the exhaust brake coming on with the idle turned up? If so shut it off. Having the exhaust brake on with the pto on will more than double the fuel used , and can cause overheat if it's out of adjustment.

Well its been a couple of weeks and the driver is reporting with the Exhaust brake off and the idle raised with the Cruise Control for PTO operation, the Overheat condition has disappeared. He stated he's been on scene for 15 minutes operating the PTO with zero movement up on the temp gauge. Thanks So much for the help its truly appreciated. Would this mean then that the Exhaust brake is out of adjustment?