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Discussion Starter · #1 ·
So, like the title states I ran into a problem on my single-turbo 2jzgte AR5 manual IS300. It’s on an AEM Infinity with protections for lean out, over temp, over boost, and low oil psi.

So I had not driven the car for a few months while fitting a LTuned bumper. I’d start the car and let it warm up about once a week or two. I got the bumper fitted and took the car out to drive it. I did not flog it at all (5psi boost max) and it was a short trip, came home and parked the car.

I started it a week later and noticed the temp gauge was climbing at idle. I swapped thermostats and temp sensors, but the issue persisted. The thermostat would not open despite the ect registering 200F (basing this off the upper vs lower rad hose - I never let the car get too hot while testing). It was as if the sensor was hotter than the thermostat. However, the car would not overheat if I took out the thermostat and manually jumpered the cooling fans “on”. I did a compression test and found #2 low at 30psi (all other cyls were in spec 145-155 psi). Head gasket, right? But there was no coolant in oil or vice versa . I could not appreciate any bubbles in the radiator. I did not see any smoke from exhaust or smell sweet coolant.

At this point I should have done a leak down test, but couldn’t find my air chuck. So I pulled the engine/trans last week. I finally got the head off last night. I couldn’t see any obvious damage to the head gasket or burnt valves. No spit shims, valves appeared to be closed. I took the head to an engine shop to be cleaned and checked for cracks, so I am awaiting a report on that. The #2 piston looks like the other 5. The cylinder bore doesn’t have any gross scoring.

What is the consensus? If the head checks out should I clean the block surface, install a new gasket, compression check, and send it?
I’d think maybe the piston rings since the compression came up on a wet test…but rings won’t cause over heat (that I have ever heard). It’s a head scratcher. Anyway, if anyone has insights I would appreciate the info. Thanks for reading.
 

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2002 Lexus IS300
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Leak down test might have confirmed a bad head gasket but you already have it all apart. If the head comes back ok (triple check for cracks) then get a new head gasket and send it.

Were you fans turning on automatically? Not sure how they are setup to turn on but reading that you had to manually jump the fans makes me thing they weren’t turning on when the temps were climbing in the first place. That might be your actual problem.
 

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Discussion Starter · #4 ·
Leak down test might have confirmed a bad head gasket but you already have it all apart. If the head comes back ok (triple check for cracks)
Yep, I’m a dingus. I couldn’t find the spark plug-to-air chuck adapter so I just called an audible and yanked it.


Were you fans turning on automatically? Not sure how they are setup to turn on but reading that you had to manually jump the fans makes me thing they weren’t turning on when the temps were climbing in the first place. That might be your actual problem.
Yessir the fans worked fine prior. I didn’t word what I meant very well. The fans are still on the stock ecu. They would come on when the sensor in the radiator commanded “on”, or if you turned on the AC. ( I do have my Infinity set to sense when the fans are on, so it can boost idle rpm via DBW). So I took the tstat out, and jumped the fan switch wires to command the fans “on” as a test, and it never got over 160F via OBD at idle.

So the car would show over temp on the factory gauge. OBD port would show temp 225+ (This is via the ECT sensor in the upper water neck on a GTE). But the thermostat never would open. It’s like the temp was locally high near the stock ECT. My AEM coolant sensor would register about 60 degrees colder - it’s in the upper rad hose with an adapter, further away from the stock ect. But the lower hose never got hot, the lower rad never got hot. I tried multiple thermostats with the same outcome. I stuck my boroscope into the back of the water pump to confirm the impeller was still attached and spins. The heater produced heat like normal.

I couldn’t tell much with the gasket, it’s the stock multi layer steel type, so hard to tell. I’m no expert but it looked OK. The bore on #2 still has the factory cross hatch to it. Oil will stand on top the piston overnight.
 

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You can blow between cylinders, so it might have gone there and been pushing air out the intake or exhaust on the next cylinder till it got to a point the gasket would hold pressure again. On a compression test you may not have noticed with the other plugs out, you wouldnt see any air through the water or muck in the oil. The last few gaskets i have seen have blown this way. The rest is either cracked head or valve seat, or burnt valve face. Any chance it has leaned out and melted a piston a little? Or rings? Lol i think that covers all the bases

I guess risk of putting it back together is you will waste a few gaskets if you have to pull the bottom end later, but on the flip side it will be a more major repair then anyway so what's a few gaskets if you know what i mean. Also most likely culprit is the head gasket so i think with the main checks you have covered most of the bases. If it were me and the bores and pistons all looked sweet and the head checks out and has been skimmed i would probably throw it back together and see what i had.
 

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Discussion Starter · #6 ·
The rest is either cracked head or valve seat, or burnt valve face. Any chance it has leaned out and melted a piston a little? Or rings?
Hopefully the machine shop can tell if there’s a head or valve issue. I have never leaned the engine out in the 5 years I’ve had the swap.

The Infinity ( and other standalones) have protection schemes built-in. I know nothing is fool-proof, but it does give some headroom. You set a rpm limit and if the AFR (or ECT or Oil psi or boost) goes to high, it cuts spark and fuel. I have engaged the boost cut just to see what it feels like, but it’s never leaned out on the ID1050cc injectors.

you will waste a few gaskets if you have to pull the bottom end later, but on the flip side it will be a more major repair then anyway so what's a few gaskets
This is the way.

Say the head/valves come back good. I get a new head gasket, and some ARP head studs. Could I put it back together without the cams? Slap the flywheel back on, bolt on the trans and starter. Then comp check it? Or just bolt on the head, gasket, leave out the cams and then leak down test it? I know it’s lazy but if it works and tells me what I need to know, it’s good - right?

If the bottom end is fubar’ed I think I will get a PowerDynamix short block. I am planning on getting a McCleod twin disk since it’s all apart anyways. I will pull the two oil pans, reseal them and install a new oil pump while I am at it.
 

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Hopefully the machine shop can tell if there’s a head or valve issue. I have never leaned the engine out in the 5 years I’ve had the swap.

The Infinity ( and other standalones) have protection schemes built-in. I know nothing is fool-proof, but it does give some headroom. You set a rpm limit and if the AFR (or ECT or Oil psi or boost) goes to high, it cuts spark and fuel. I have engaged the boost cut just to see what it feels like, but it’s never leaned out on the ID1050cc injectors.



This is the way.

Say the head/valves come back good. I get a new head gasket, and some ARP head studs. Could I put it back together without the cams? Slap the flywheel back on, bolt on the trans and starter. Then comp check it? Or just bolt on the head, gasket, leave out the cams and then leak down test it? I know it’s lazy but if it works and tells me what I need to know, it’s good - right?

If the bottom end is fubar’ed I think I will get a PowerDynamix short block. I am planning on getting a McCleod twin disk since it’s all apart anyways. I will pull the two oil pans, reseal them and install a new oil pump while I am at it.
Put the cams in. You can do a compression check with the engine on the stand just fill it with oil and make sure you timing belt is on. Then 12v to your starter and solenoid and it will crank over. When you machine the head you'll need to adjust your valve lash so you need to do that before you can test compression.
 

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Sure sounds like blown HG. Based on your synopsis, seems highly unlikely it blew on account of knock; so an overheat is suspect.

My prediction is the machine shop will report that head was warped a bit.

Still, considering the failure mode is not fully understood, I'd check for proper engine sealing with the least possible amount of work/assembly... Which would be a leakdown with the head on, no cams, no timing belt, no oil pan, etc

If it leak tests good, you'll need to carefully consider how it overheated.
 

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Discussion Starter · #10 · (Edited)
highly unlikely it blew on account of knock
Yep doubtful of knock. Never leaned out - has lean out protect that’s never engaged. Also running dual Bosch “wideband” knock sensors that did not alert a knock problem.


leakdown with the head on, no cams, no timing belt, no oil pan, etc
That will be the plan, then. Will have to wait till the shop gets the head checked, and I get a set of ARP studs and a new HG.


If it leak tests good, you'll need to carefully consider how it overheated.
Well, it’s never overheated until now. And it’s only overheating on the stock ECT sensor in the upper water neck. The Infinity is getting its sensor reading from the middle of the upper radiator hose, so the water temp is cooler there VS the stock sensor location. It’s like it’s getting hot closer to the engine, but the tstat isn’t hot enough to open ( it works because I tested it in a boiling water pot). The top of the rad gets hot, but not the bottom of the rad. I was afraid to let it get much hotter to try and see if the tstat opens.

Will a HG just “blow” randomly? It’s the stock MLS type. I have ran the yota pink (SLLC) since before I was GTE. The engine was a 1998 Aristo model, so it does have age but there’s tons of old cars on factory HG. God knows how beat on the engine was before I got it. Was one of those “100000km” motors. Probably sat in a Japan junkyard for years. But it’s r an like a top for the last 5 years, too.
 

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Discussion Starter · #12 ·
When you machine the head you'll need to adjust your valve lash
Decking the head will change the valve-to-piston clearance, but it won’t affect the lash (cam-to-bucket clearance). You are right, I will probably do a comp check or leak down when I get the head back and some studs/gasket.
 

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Discussion Starter · #13 ·
So I ordered a replacement head gasket and some ARP head studs. I will work on cleaning up the block mating surface while waiting on the machine shop and parts to arrive. Any tips on getting the deck clean?
 

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I've always used a combination of of elbow grease and utility knife razor blades. The trick to this is not over-using any one blade. Switch them out early and often.
Same, though i have a few scrapers i use which is pretty much the same thing. Also used a 1.5" chisel once when in a pinch which worked well, just got to not go overboard so you dont mark the block. I also go over with a stone just to make sure all the high spots are gone, but thats my toolmaker background kicking in lol.

I would agree, get it together with minimum parts and do the compression tests and see how it looks. My bet is it will be fine. As for cause, sometimes it is hard to say for sure. I havent done one for 10 years or so now, but i do remember the last couple didnt have a specific cause like water pump or thermostat etc. All i could think of is time and heat and beatings had eventually taken its toll. Also when you think of it the center of the engine is probably getting hotter than the outer walls so would be where the gasket is under the most extreme. A little unseen extra boost, a little extra unseen heat, a little stretch or uneven head stud torque, etc. can all sometimes happen without knowing. I am not saying its any of that but you know what i mean. ;)
 

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I also go over with a stone just to make sure all the high spots are gone, but thats my toolmaker background kicking in lol
I'm anal retentive about introducing grit into engines, so I would not sand or stone an assembled shortblock I couldn't thoroughly clean afterwards.

Do you have your Journeyman Toolmakers card?!? If so, that's badass. Dying breed. Much respect!

Know the difference between a machinist and a toolmaker? A toolmaker is a slow machinist!

;-)
 
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