Pictures for attention:



For the full story, read in numerical order (1,2,3,4)

4) THE PROBLEM:

The engine runs really rough after overheating. I tore things down and fixed what i thought the problem was, and it fixed everything... UNTIL i started driving and the car warmed up. As soon as it got warm, it started running just as rough, not wanting to drive, whole car shaking, won't go over 40ish. There is also grayish reside on the firewall directly behind the engine, and hoses around there.

I tore back into it and checked spark plugs 1/2 and 5/6; they're dry. I didn't have time to check 3/4 due to the TB, but i doubt there's coolant in them either. I'm now at a loss of what this could be.

I'm concerned it could be a head gasket due to the gray residue on the firewall. I don't know if it's the boiling coolant that dried, or if hot gasses are escaping back there.

My next steps are to check spark plugs 3/4, replace the spark plugs, and compression test the engine. Also pressure check the coolant system.
However, neither of those would explain how it ran (and drove) perfectly fine until it warmed up, unless the thermostat opened and coolant was still leaking onto the plugs, which i didn't see.


3) WHAT I'VE DONE:

Got back from vacation, refilled the coolant, and went to drive it. Ran rough, everything shaking, etc.

Came back the next day after thinking all night about it, decided to tear into it.

I figured there was coolant in the spark plug galley, and boy was i right. (it ran like that once after i power washed the engine bay.. ) Pull the plug wires and they were soaked. So i tore it down, shop vac'd the coolant out, dried off the plugs, etc.

I saw some smoke from the back of the engine bay when it was running, so i suspected the heater hose in the back busted under the pressure of overheating. Replaced it and noticed it didn't have any cracks/noticeable holes. Weird.

Got everything put back together, killed the hornet in my door jam building its nest , fired it up and everything ran just like it used to. No problems at all. Started driving, everything was fine, then it warmed up and it started to do the same thing, getting increasingly worse.


2) HOW IT HAPPENED:

Everything started with a squeel.
Turned out to be my bearing on my tensioner pulley. I drove it a little too long as I didn't have time to replace it before vacation, and on the way to the airport it seized up.
Belt shredded, wasn't very noticeable while driving other than PS went out and my battery light came on.

I drove it a few more miles not even thinking the serpentine belt drove the water pump, looked down and the temp gauge was peaked. Shut it off and coasted into a parking lot.

Coming from the MKIII world, i knew i ****ed up. Overheating a 7M means don't even diagnose, just pull the head and do the full headgasket job.

I replaced the pulley/belt and drove it to my brothers maybe 2 miles away. It was running rough, but that's not surprising. I didn't have time, so i parked it and let it sit until i got back from vacation.


1) A LITTLE BACKGROUND OF ME:

Not much of a poster here because there's a lot of helpful information throughout all the threads.

Got a '92 SC300 that I got for a good deal, all original 2 owner (basically one owner) with every service record since it rolled off the lot, all performed by the Lexus dealership. Since there I've done plenty of upgrades, but they've all been cosmetic. The engine is still completely stock.

I come from the MKIII Supra world, and have had those 7M engines torn down a few times, with quite a few upgrades to mine. (more so performance than the SC)

Long post, so I'll keep that part short, any questions feel free to ask.

Any help, insight, knowledge.. whatever you have is greatly appreciated.

 

Well sounds like you overheated multiple times which is not a huge deal for the 2JZ, their is a common heater core house that leaks right behind the head I would start with replacing that and putting a nice new clamp over the hose......

 

Also, check your heater control valve as you may have cooked that.... It is a very expensive OEM part no real after market options. A lot of people just bypass it but then no heat in the cabin.

I had 2 back to back over heats (one blown water pump and one above mention heater control valve failure) and 2 months later the head gasket went. All fixed now and feels like a new car.

 

you probably blew the headgasket, its not hard to do from overheating even though the engine is a strong engine (good possibility you also warped the head at the same time), they pretty much blow out the gasket and warp the head on the first good overheat (driving around when warmed up without a serpentine belt is a good example of a good overheat). do a compression test it will help figure out the next step. the coolant probably leaked when there was too much pressure or possibly from running at higher speeds the combustion pressure was entering the coolant system causing the hoses to leak (they just have spring clamps on them nothing that will hold major psi). It probably wasn't due to the hose being faulty, If you run it hard it might do it again I suspect, but at this point do a compression test, or a leak down test if you really want to get involved. Only real way to know will be to pull the head and put a straight edge across it as well as inspect the gasket, there isn't much else it can be and since the engine is running terribly, then its probably going to need to happen anyways.

 

Maybe the way I wrote the post is confusing, but it only overheated once. It's pretty much been sitting ever since.

I already replaced the heater hose on the back of the head, clamps are good.

The car does not have a problem with overheating, it was just that one time. I've let it warm up and driven it a little bit (until it started running rough again) and it didn't heat up any more than it would before this happened.

The only reason i don't believe it's a head gasket is because it was running perfectly fine until the car warmed up. (that's after fixing it after the overheat) If it was a BHG, the car would run like crap even before warmed up because of compression issues and coolant in the oil already.

I'll be compression testing it today anyways. I'll see what i can find out,

 

Well the 200k mile mark was rough, but I got it running back to normal.

New spark plugs was all it needed, but i went ahead and pressure tested the cooling system for safe measures. Holds steady while running so no internal problems.

These engines are resilient.

 

Amazing. My luck it would've been a bhg with a warped head. And I'm not one to beat on engines.

 

There's actually a thread dedicated to this topic full of non-lexus heater control valve options. I personally used to run one from a F-150 and currently run one from a Volvo 240. Both cost less than $20 to replace.

https://www.clublexus.com/forums/per...rol-valve.html

 

I was disappointed you went back with the crossover pipe