1HZ EGTs (1 Viewer)

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Feb 25, 2010
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I’ve got experience with NA 3Bs and 3B-Ts but my HZJ77 is my first experience with a 1HZ.

To get straight to the point - I certainly realize that this engine is “limited“ in its power and that’s fine with me BUT it’s also seems to be rather hard to keep EGTs within reason AND have access to ”high speeds” like 55 and less. At 55 in 83 degree ambient temps on flat to somewhat rolling highways/roads the engine RARELY sees anything under 700 degrees EGT and often times will run to 850 or 900 degrees. If I try and keep the same throttle position she’ll got to 1000 or 1200 degrees EGT. What worries me is this: If the truck was “quick” - it’s an auto by the way - it would be one thing, but it’s slow - which I accept - AND runs high EGTs. Going up a mountain here in VA I kept her at 25mph and slower all the way up for maybe 2 or 3 miles and she hit 1250 degrees AND saw coolant temps pushing 210. On the way down the mtn she quickly came back down to 180 coolant temp and 400 or 500, and less, on EGT coasting.

The engine idles smoother than a new Lexus and starts if you so much as look at the key. She doesn’t burn excessive amounts of oil and the coolant level has NEVER gone down. It also has a larger aluminum radiator and has a total of maybe 90k miles on her. It’s a constant battle to keep EGTs down AND maintain 50-60mph on a relatively flat road. My fear is that turning down the fuel would make the truck wholly incapable of keeping up with a Honda Ruckus or electric skateboard. Any advise?
 
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I posted this in diesel tech as I realized this probably isn’t the spot for this post.
 

Gun Runner 5

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Properly tuned + Intercooler.
image.jpeg
 

GTSSportCoupe

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Just a few thoughts off the top of my head.

First, is the auto trans shifting properly? Does it need kick down adjustment? Are you running bigger tires? Running higher rpm's can help drop EGT's in many cases. Simply moving more air through the motor helps a lot.

If you want to maintain power (not turn down fuel), but drop EGT's, I'd be looking at intake/exhaust flow improvements. This will get more air through the motor, thus dropping EGT's. Oddly enough, headers can help move a lot of air through a 1HZ, and adds a nice power gain.

Monitor your trans temperature. When those A442's are out of lock-up, the torque converter dumps a lot of heat into the radiator. Add an external trans cooler in addition to the radiator trans cooler; this will help dump the heat (put the aux cooler in line before the rad trans cooler).

Look at servicing the viscous fan hub also.

Turbo will reduce EGT's, but it'll also tax the radiator even more. And you'll be tempted to add more fuel for more power, which will make things worse.

Best if you want power and cool, is install a 1HDT with H55 transmission. Direct injection motors are more efficient and loose less to coolant.
 
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She may need a kick down adjustment. The way it shifts to high gear makes it feel as though the top gear is WAY tall.

Transmission temps stay pretty darn cool.

Tires are bigger - 33’s.

Wont be doing any engine swaps I don’t think.

Ive thought about putting a turbo on it w/Intercooler. Not to make big towing power but in hopes of bringing a bit more efficiency to the engine but at 22:1 compression that spooks me.
 

Gun Runner 5

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Everything GTSSportcoupe said is spot on however if you don't have the budget for a 1HDT there are still options.
I've driven the exact same vehicle (77 Series + 1HZ). I drove it both normally aspirated and turbocharged / Intercooled. I have a 1.5 mile steady incline leading into my house and prior to the turbo I would see 1,100+ degree EGT's and a steady loss of speed. (Sound familiar?)
With a properly installed and tuned turbo (plus Intercooler and 2-1/2" - 3" exhaust) those temps dropped to 600-700 degrees and very little, if any drop off in speed. Perhaps not a cheap solution but a solution none the less.

**Are you relying on the factory transmission over temp light?
 
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Feb 25, 2010
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Yeah - I love the engine - tough and durable - there‘s no doubt in my mind the engine can be made to drive on a flat road at 55 without melting itself. I can’t see Toyota designing an LC incapable of moving itslef up a hill at 25mph at EGTs below 1000 degrees.
 
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Even though I’ve never had the gauge move much? I don’t tow more than a motorcycle once in a while....
 
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Everything GTSSportcoupe said is spot on however if you don't have the budget for a 1HDT there are still options.
I've driven the exact same vehicle (77 Series + 1HZ). I drove it both normally aspirated and turbocharged / Intercooled. I have a 1.5 mile steady incline leading into my house and prior to the turbo I would see 1,100+ degree EGT's and a steady loss of speed. (Sound familiar?)
With a properly installed and tuned turbo (plus Intercooler and 2-1/2" - 3" exhaust) those temps dropped to 600-700 degrees and very little, if any drop off in speed. Perhaps not a cheap solution but a solution none the less.

**Are you relying on the factory transmission over temp light?
No wonder.... you push more air and add more fuel to get more power... More air = cooler EGTs. As long as you don't add too much fuel you have more power and cooler EGTs.

Without turbo to get more power you add more fuel your AFR drops and your EGTs are climbing... you keep choking it with fuel and it slows down even more...

By shifting down you make your NA engine breath a bit better but your coolant temps are not getting much better...
 

mudandrock

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I think GTSsportcoupe is on to your problem. Almost always, when a customer calls me telling me their 1hz has a cracked head, it’s an automatic transmission behind it. The mechanical a440/a442 does not respond to downshifting as it should and shifts into overdrive too early, both these scenarios make too much heat. Try leaving your shift lever in position “3” and only shift into overdrive when you’ve reached highway speeds. I consider these transmissions to require some manual help. Do this before you even consider a turbo.
 

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