Misfires and coolant on top of spark plugs

Revoker · Dec 27, 2018

BACKSTORY: My engine head was recently rebuilt by a Mechanic/Machine shop who did all of the work. The block wasn't touched but was inspected for flatness. The head was put in an oven and then sandblasted to clean off everything. The day my car started acting up I had installed a boost gauge, wideband, AFR gauge, and intake pipe.

SITUATION FACT: My 1990 supra 7mgte has bad misfires at idle and at almost any rev range. Looking into my engine there are pools of fresh radiator fluid (coolant) covering the top of the spark plugs in the valley between the 2 valve/cam covers causing misfires and rough driving.

FIXES: 12th DEC→24th DEC- Removed and cleaned all the spark plugs. Cleaned the spark plug well of coolant and replaced the rear coolant heater hose because of possible pinhole. Ran fine for a while and then started misfiring again. Opened up to find it refilled with coolant.

I Believe these are the spark plugs in order. #4 is the cylinder with the most coolant in it and the spark plug looks like it isn't burning the fuel.

PROBABLE CAUSES: Reading around the net I saw some threads that said it could be the valve covers (doesn't make sense since it is clean coolant and not oil). Others said it could be the throttle body leaking coolant, but since there isn't coolant on top of the "No. 3 Cylinder Head" gasket/cover (there was some on the bottom of it) I think it has to be coming from inside the spark plug valley/well and not from a hose above the valve covers. I'm thinking it has to be the "freeze plugs" in the spark plug wells. I'm guessing they are leaking because of the heat treatment and sandblasting that the head recently got. I also asked the machinist who worked my head and he said the "freeze plugs" aren't likely the cause. Then I asked about if it was a crack from the work and he also said no, and that it would more likely be the plugs instead of a crack.

PLANS: I think I'm going to order the plugs from toyota (heard aftermarket is a shit show for these) and replace them and/or bring it back to the mechanic that did the work (But they don't open till 2-JAN-2019 because of the holidays and I might not feel like waiting)

NOTE: I don't drive my car that much. I drove it twice in the 13DEC→24DEC time period for a few hours each with about 6→12 engine cycles between the 2 events. On the 2nd drive (towards the end) is when I noticed the stutter.

VIDEO:

RESEARCHED THREADS:
https://www.supraforums.com/forum/s...s.com/forum/showthread.php?664950-Oil-Water-In-Your-Spark-Plug-Galleys-Write-Up
http://www.toymods.org.au/forums/threads/67381-How-to-remove-water-gallery-plug-7mgte-head
http://www.toyota-supra.info/forums/mkiii-supra/16449-coolant-on-top-of-spark-plugs.html
https://www.supraforums.com/forum/showthread.php?244785-Fluid-in-spark-plug-galley
http://www.mkiiisupra.net/bbs/7m-technical-section/40539-weird-issue-help.html

JOutterbridge · Dec 27, 2018

Coolant only gets there like that for a few reasons. I'm sure you'll have it figured out soon. I would re verify coolant levels and then check car again while idling after cleaned up. Then under vacuum, low RPM for a few miles. Then check the higher RPM range to see when it's pooling up the most or if its constant

plaaya69 · Dec 27, 2018

Those 4 caps you took off encounter oil only. The 3 big plugs between 1-2, 3-4 and 5-6 spark plugs is where coolant flows underneath them and those are usually the culprit for this type of coolant leak.

Revoker · Jan 22, 2019

Ok some good news and some bad news.

First I fixed the leak. It was those coolant caps/freeze plugs that you guys and I thought it was. I took the plugs out, cleaned them up and then put loctite blue threadlocker on the threads. They leak a little bit but no where near how much they used to. I did notice that it was completely black underneath the caps and it kind of looked like some loose deposits (the bottom of the cap in the 2nd picture is what it looked like underneath).

The bad news is that now I have foam coming out of my radiator. I think its possibly from the excess loctite blue threadlocker I used, but I'm not sure. I used 2 bottles of flush cleaner to try and clean it out (used at separate times). But on the first time of trying to use the flush the car overheated after a 30-40 min drive and 10 min idle (its also possible I didn't have enough reservoir coolant at the time). The temp was middle during the entire drive, it wasn't until I parked it and let it idle for 5-10 mins that it rushed to hot and started to boil over. The foam was leaking out as soon as I had gotten back from driving though.

I have since Flushed it with again (less driving this time). Then flushed it with only straight water 2 times. Foam still comes out even after I had pulled the thermostat, upper/lower radiator hoses and flushed the block with water.

What do I do now? I was thinking of using a tester for a BHG, but I did just replace it with a MHG and ARP studs, and I don't think foaming is really linked to a BHG. Plus this started happening after I added blue loctite to the water galley plugs.

madisonMK3 · Jan 22, 2019

I would do a leak down test with my compression tester + air compressor

fill each cylinder up w 140 psi, one by one (on tdc for each respective cyl) and see if its bubbling coolant out

if the block was not decked (you say block was not touched) I would have my doubts on the metal head gasket sealing

the combination of foam and overheating is strongly suggesting BHG...

Revoker · Jan 22, 2019

That's really is my worst nightmare, but it is what I was thinking.

I'm ordering a coolant combustion gas tester to check it out tomorrow and will possibly get a bleed down done at the machine shop. This just is all really shitty timing. Fixing one thing to find another. Thinking about it now though, im guessing it could have always been blown but the gases were escaping from the water galley plugs and when I fixed them they had nowhere else to go.

Misfires and coolant on top of spark plugs

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