@2001LC What intervals(s) were coolant changed at? Lots of opinions and rumors over the years as to cause on many Lexus/Toyota products with these issues. I’ve seen everything from bad FIPG by a robot, coolant acidity, to a greasy chip eater on the assembly line.
These are well regarded SAIP bypass kits
Find compatible Secondary Air Injection Bypass Kits and Kit Addons for your Toyota or Lexus Truck and SUV.
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This one had extra coolant flushes and refreshes. Radiator cap and thermostat replaced at 88K. No sign of every running hot. One coolant refresh before 88K (1st owner) with water pump at 65K. We did flush at 88K and 10 years as a PM. It than had timing chain cover oil leak repair, so would have been another refresh ~95K. I just did another full flush at 121K miles.
I've heard/read the talk of grease chick eating fingers of assemble workers, bad robot, bad day FIPG. All are possible. But I'm just going I what I saw and my experiences with other engine.
I’m just a guy writing on the internet but the pictures posted in the last page tell the story. RTV should not vary from being that thin near the bolts to that thick between them. Period. As the cover and block expand/contract the RTV has no choice but to eventually fail due to the material shearing at different rates.
I actually wonder whether marginally less torque could help prevent future failure. A better RTV likely would. Stiffening the cover somehow.. ultimate fix, but also impractical.
I do know if I ever dig into this I’ll be cleaning the threads, using new bolts, and a calibrated in-lbf torque wrench to put the specified value closer to the middle of its range. IMO bolt torque and ultimately the correct clamping force (meaning not too much) is critical to this all working.
I'll add a little more.
Toyota FIPG is known as same of the best there is. I just don't see leaks from it. But my specialty is the 4.7L of the 100 series. We don't see factory FIPG leaks or proper shop applied fFIPG, leaks.
The valley coolant heat lid is only place I saw coolant was getting between it and FIPG. FIPG was remaining on block too, and without signs of coolant getting under it. There was also a large ring of FIPG, hanging from lid as I removed it. This would have been excess FIPG that squished inward when assembled. There was also some FIPG visible on out side seam, pre-disassemble. So it had more FIPG applied than needed. Uneven torquing down in stages, form factory although possible not likely. It appeared to me as if the lid expanded between bolts.
Interesting though on torque
@bloc . But 4.7 has some lower, high and mixed:
We don't see this in water inlet to water pump FIPG joint of the 4.7L. Which is torqued to 13ft-lbf. But it is very stiff & thick aluminium and only about 6" total surface. I've seen those at 250K miles and 20 plus years old, without any leak from factory seal FIPG joint. I compared these 5.7L valley water heat lid in size, to oil pans in the 4,7L. 4.7L oil pan #1 is aluminium. They have ~16 bolts & nuts with much less distance between them. With a torque spec of only 66IN-lbf (~5ft-lbf) on their 10mm bolts, but 31 ft-lbf on their 12mm. Those are factory FIPG oil sealed. Second oil pan is steel, FIPG oil seal, with same bolt spread and all 66In-lbf torque. I've seem oil pan of 20 plus year old 500K miles 4.7L, but never seen a leak. Seen the 4.7L over-heat to point engine and all rubber hose change color, head warp and plastic intake manifold melt. Still no leaks at factory FIPG water inlet or oil pans. Even the 1 million mile 4.7L USA built Toyota, didn't "report" any leaks. The 98-02 Transmission is also FIPG seal, with same close bolt spread & light torque of 4.7L oil pans. Yet never see them leak.
We'll never know for sure why. But I can say I cleaned, applied FIPG and torqued in stages and cross start pattern to spec, doing the very best job I could. I have concerns! where I normally do not.
