Dead Head (gasket)

Welp....
I think my 3RZ may have a blown head gasket. I recently had the coolant flushed (and thermostat changed to new OEM) and it was a gross oily brown with a bunch of deposits in the overflow bottle. Ever since that flush whenever the heater is on I can continuously hear bubbles going through the heater core, no matter how long it has been on and burping (most of the time the bubble frequency changes with RPM). On top of that, a couple of days ago on a cold morning I had a few obvious dead misses (type of misfire) right as it started up, they went away and haven't come back and there was no CEL. I removed the OIL cap the other day while the engine was on and it sounds like the end of the exhaust inside the valve cover, just a bit more muffled, plus there is massive amounts of blow by (not just a few puffs, like every compression stroke).

Just as a bit of background, it got new plugs and wires (NGK) less than 4 months ago. When I changed the number two spark plug I noticed that it was so loose that I could unscrew it just using the socket extension (the wire had been popping off of it too, that's the original reason I was changing them). The number two plug didn't look any different but the spark plug tube was a bit crusty from what I can only assume were escaping combustion gasses.

The only other symptom I can really think of was the one that caused me to check my coolant to have it flushed and that was because my Ultragauge had started reading 212F whenever I had just come up the hill to my house. Even after the flush the engine runs more near the 190F zone and climbs to 206F after long periods on the highway.

Anyone think it could be something else? I really hope that I don't have to have the HG replaced, I don't feel comfortable doing anything related to engine timing and I don't know any competent mechanics that I would trust to properly do the job.

TL;DR - Read the wall of text, I can't shorten it and give all the facts. LOL

 

Start up the truck with the radiator cap removed.

See a lot of bubbles? And is the overflow tank at a normal level?

 

There's a test a mechanic can perform that determines if a head gasket is leaking or not. I'm sorry that I don't recall what the test is called, but they hook up to the upper tank of the radiator and test the water for exhaust gases.

It may be worth the $$ to have the test done as it may save you pulling the head and replacing the gasket.

 

if you had a shop do the flush they may have run it hot on you, wouldn't be the first time I saw a shop run a truck without water or oil after servicing it and most times you never know about it.

not sure how long ago it was but just saying this is odd to happen out of the blue without a reason and if you didn't overheat it, maybe they did. it would be nearly impossible to prove but you can call the shop and bluff saying you KNOW they ran it hot and now something is wrong with the engine, they may admit to something or maybe not but if you think they "may" have done something to cause this then try it and see if they admit to anything.

beyond that you need to pull the head to confirm its just the gasket and not a cracked block or a warped head

again, I have never seen this unless the engine was overheated a lot

 

Well, I ran the engine up to normal operating temp with the heater set to hot and other than the level gradually rising there weren't any bubbles at the top of the reservoir. What does this mean.... so confused.

 

see if your engine is low on oil, if it is then there is definitely a leak between the water and oil passages and the oil has more pressure then the water so it goes in that direction but you may also see signs of the oil getting milky in color indicating water is seeping into the oil, usually when the engine is turned off and you still have pressure in the radiator. a leak between the water and oil doesn't mean your engine will run bad because it still has good compression because that part of the gasket is still good.

 

It may have a slight leak where the water jacket and combustion chamber meet that is sealing itself once it warms up. This pressurizes the cooling system by allowing exhaust gasses to enter the cooling system.
Usually they start off small and will seal itself once the vehicle gets to normal operating temp. Eventually it will get worse causing the vehicle to start constantly overheating due to air/exhaust gas pockets in the cooling system.
Leaks like this sometimes dont show up in the crankcase.

 

Well, after weighing everything and looking at all of the evidence I think it is just a poorly bled heater core. The shop that did my radiator flush is well regarded and started out as a radiator place exclusively (they know what they are doing). They probably just didn't think that the heater core would be hard to bleed. Plus, I'm rather sure the coolant in my truck wasn't ever changed until I did it, which would lead to heavy buildup that is still leaching in to my new coolant. My engine hasn't overheated to my knowledge either.

I was reading some YotaTech threads and some TW ones as well. The heater core bubbling is sort of common in the 4.0L equipped vehicles as the head gasket has a weak spot near the 6th cylinder. However the pre-tacos (which being a 95.5 my vehicle more closely resembles) have an issue where the heater core is insanely hard to bleed (mine being even harder because it is very clogged from years of coolant neglect).

My plan is to park on a steep uphill grade (because my truck has a strong rake). Then let it warm up with the radiator cap on, then carefully remove the cap at operating temp and pulse the revs a bit. Hopefully that will draw the air out. If that doesn't work I may just hold the pedal at around 2500 or 3000 RPM as that seems to get it to bubble on the road. I wish I had some extra of the coolant that my shop used, but they said that it is universal and can be mixed with anything but DEXCOOL.