1HDFT low oil pressure - Main bearings

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I am pretty sure I know the diagnosis, but wanted some confirmation from the experts.

I've acquired the motor in 2019 to swap into my 77 series. I didn't do much to it except some preventative maintenance like water pump, timing belt, and injectors/pump before installing it. Its been a great motor, put about 20,000km since install. From the beginning, I've had a digital oil pressure gauge installed, been monitoring and mentally logging the readings. Its never been high once warmed up, FSM calls for a minimum 36psi at 3000rpm, for a while its barely made it, never exceeding 40 psi. In the last year I've been noticing it creep lower and lower. I just finished up a week long 3000km trip with lots of highway, pulling large grades, sustaining max boost and loading the engine for extended periods. Towards the end of the trip I really noticed a decrease in pressure, more smoke at start up then usual (always been smokey) and very noticeable, eye watering diesel exhaust smell for anyone trailing.

Upon start up when cold, pressure is about 40-60 depending on temp. Once warm, very quickly drops to 8 at idle, and does not go above 25psi at 3000rpm. When loading the engine, pressure would drop to about 20psi, only creep back up once coasting. I did the compression test not too along trying to diagnose the excessive smoke at startup, its was marginal on the spec as well.

From everything I've read, all signs are pointing to bottom end problems with the main bearings, and whatever else. I am pretty much committed to doing a full tear down, wanted to hear opinions. These engines are not known for bottom end failures as much as the 1HDT, but anything can happen.

Thanks
 

mudgudgeon

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A rebuild may be in your future, but I think it's worth doing some more trouble shooting.

Buy or borrow a mechanical oil pressure gauge and verify you are getting a true reading on pressure.

Eye watering diesel fumes suggests an issue with injection, not oil pressure.
Eye watering fumes are a symptom of incomplete fuel combustion. It can be a result of incorrect injection timing, or due to air getting into the fuel lines.

What colour is smoke on start up?
Blue-ish smoke suggests oil is being burnt.
White smoke suggests air in fuel, and incomplete combustion. Incomplete combustion produces eye watering fumes, and strong smell of diesel.
Black smoke is overly rich fuel mixture (combustion is complete, but ineficient and sooty)

How is the truck performing?
Running smooth under load?
Power output normal?
Starting normally?

Could be an issue with getting air into fuel lines and mucking up injection timing. This typically shows up as a stumble under load, and white smoke out the exhaust.

Maybe check the oil level on the dipstick. It is possible (uncommon) for diesel to leak into the sump and dilute sump oil. This could impact oil pressure.
It also puts you at risk of the engine running away uncontrolled by burning the sump/diesel oil. Diluted oil will get past rings more easily, and can lead to rapid ring / cylinder wear and the engine burning it's own oil as fuel.

When you did the compression test, did you also do a leak down test?
 
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@mudgudgeon Thank you, great info to consider.

The smoke is primarily only at start up until it warms up. The smoke is thick white, even letting it idle a while, upon first drive it belllows heavy as if its burning something off. I live in Socal, it never gets really cold, even at mild temps it smokes. Once warm its fairly clear. I advanced the timing and that helped.

Once warm the engine runs fine, normal power, stable throttle and idle, no weird noises. Engine temp holds solid. It starts up easily. It does stumble with throttle when it is still cold, is that normal?

Based on your explanation, air could be the cause of my symptoms. I've replaced lines, filter housing, did the clear tube thing. I have yet to touch the pump, could it be getting in through there? Maybe I should get that checked/rebuilt before diving into the engine itself?

I had the oil tested not too long ago, that did not reveal anything abnormal.

Plan on dropping the pan and checking out the BEBs and what I can see of the main bearings.
 

mudgudgeon

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@mudgudgeon Thank you, great info to consider.

The smoke is primarily only at start up until it warms up. The smoke is thick white, even letting it idle a while, upon first drive it belllows heavy as if its burning something off. I live in Socal, it never gets really cold, even at mild temps it smokes. Once warm its fairly clear. I advanced the timing and that helped.

Once warm the engine runs fine, normal power, stable throttle and idle, no weird noises. Engine temp holds solid. It starts up easily. It does stumble with throttle when it is still cold, is that normal?

Based on your explanation, air could be the cause of my symptoms. I've replaced lines, filter housing, did the clear tube thing. I have yet to touch the pump, could it be getting in through there? Maybe I should get that checked/rebuilt before diving into the engine itself?

I had the oil tested not too long ago, that did not reveal anything abnormal.

Plan on dropping the pan and checking out the BEBs and what I can see of the main bearings.
That sounds like you may be getting fuel bleeding back to the tank while parked. You may have a small leak letting air in to the fuel system while this happens.

When you get air in the fuel, the internal pressure in the IP becomes unstable because air compresses.
You will not get sufficient pressure at the injectors to crack then reliably at the right time.
This effectively regards the ignition, but you also won't get the right amount of fuel, and retardation might be inconsistent/ not at every injector for every cycle.

Maybe recheck for air in fuel with a clear tube at start up. Set it up, and run it (so the clear tube is full) before letting the truck sit as you normally would.
Have someone start the truck while you watch.

Could be filter o-rings not seated properly. Or s hose not quite sealing at a hard pipe connection
 
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From everything I've read, all signs are pointing to bottom end problems with the main bearings, and whatever else. I am pretty much committed to doing a full tear down, wanted to hear opinions. These engines are not known for bottom end failures as much as the 1HDT, but anything can happen.

Australian owners were still having problems with the 1hd ft and fte versions. Not in big numbers but still happening. Some owners had to sign confidentiality agreements with Toyota Australia to get their FTE fixed. One owner reported that their 100 series 1HD FTE had had the BEB done 3 times in 300000klms.

I think your diagnosis looks accurate. But they can go for a long time with low oil pressure and a gentle foot. The oil pressure at idle is not all that important as long as there is some pressure.
 

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