New head gasket, now poor mileage & performance?

2008 4x4, 4.0 V6 access cab TRD off-road.

Had my head gasket replaced, new spark plugs, heads machined, new radiator, and transmission fluid flush/replacement completed at the Toyota dealership in Tucson. Now, 300 miles later, I am getting only 14.1 mpg around town (versus 17+ that I've gotten for 10 years). It also feels like my truck doesn't drive with as much "oomph" as it used to, especially in the 15-40 mph range, like it is hesitant to shift or something. Or like gas is slow to get into the engine or something - I don't know how to exactly describe it, other than it just feels weak.

Additionally, about 50% of the time when I start it in the morning and the RPMs drop from 1.5 to 1, there is a nasty, quick grinding/scraping sound, like metal on metal, but only for a second. Never did this before until the repair.

Does anyone have any possible ideas to what may be at play here? I would like to go back to the dealership with some bullets for them to check because they already tried to screw me 2 times during the head gasket repair. Timing belt? Catalytic Converter? O2 sensor? Something with the exhaust system?

To be perfectly honest, my truck felt and performed better BEFORE the head gasket replacement (it had a crack and I used the Blue Devil bandaid). Example, I consistently got 19-20 mpg (mix of city & highway). Also, within the last year, had a new water pump and thermostat installed as well.

I am pretty upset that I spent $4400 for my truck to seem WORSE than it did before.

Thanks for any and all help!

 

Can you describe in detail what they machined on the head? Did they deck and plane the head mating surface? I'm told that's a no-no with these motors/heads and may affect cam timing and VVTi activation which might be part of the loss in performance. @Torspd knows...

 

Whatever they machine off the head in terms in thickness needs to be added back. This is why cometic head gaskets come in different thicknesses. .

 

Plane and simple. See what I did there?

 

Roger. I tried calling today to mention what was going on after 280 miles post-repair to get it documented (supposed to bring it in at 1000 miles) and the "advisor", which I have already had trouble with many times, said "just bring it in".

Also, not sure if this is useful information, but I am fairly confident that the poor performance/shifting issues seem to happen only when in Overdrive? Which is odd, because for 10 years that was the default way I drove the truck, and now suddenly I am having issues.

Thanks for the help all.

 

How much did they machine off? How much quench is there in the gaskets that they used? Any aftermarket internal upgrades or oem? The ideal “quench” for a standard compressed head gasket is .040. So the head gasket comes into play on how thick it is once compressed. There is a .005 room for play of quench and should never go below that. Maybe they just f’ed up putting it back together.

hopefully they did not reuse the old head bolts. Was the oil pump reprimed before starting it after replacing?

The timing correctly done?

Hopefully they didn’t take off more on the heads and block than the quench could make up for. Hopefully your pistons are not smacking against the valves. When you start it, where is the noise coming from? On next cold start have someone else start it with the hood open and listen. Dumb question kinda not really to ask them, did they take all the carbon off the piston heads and valves and clean everything before putting it back together?

could be a bunch of chit. But without actually knowing exactly where it is coming from is hard to say.

 

Also did they put the old valves back in? If so did they put each one in their respective place that it came out of and how did they seat in there? Did they lap them? Put new valve seals in as well? Valve seals should always be done when doing heads. If they lapped them, how did they lap them? What did they use to lap with. Was the valves and heads entirely free of carbon?

 

I hate dealers lol. They just want your money and have shitty mechanics in my opinion.

 

Sounds like they may not have done the transmission change correctly.

maybe didn’t temp check, or add enough fluid.

don’t think the head gasket repair is the issue here

 

Or they could of done everything correctly and the transmission flush just f’ed it all up. It’s a 50/50 on doing transmission flushes

 

I would be curious to know what initiated the head gasket failure. If you overheated the living dog piss out of it, pistons, rings, and cylinder walls could be trashed causing low compression.

 

Or it could be as simple as loose hoses in the engine compartment. Make sure all the hoses are connected completely and no loose or cracked hoses. Lol. It could be a multitude of things

 

Just had a buddy bring back his 3RZ 1st gen that I installed a reman head/ new head gasket/new head bolts/new ex manifold and full tune up on last fall. Misfire code on Cyl #2, running poorly. Fudge me.

After cursing my life, it turns out it was a faulty factory spark plug. $1.78 part. This, too, could be a lot of things. I hope it's as simple a fix as my last conundrum.

 

Punny....very punny. Lol

 

i had this same problem, i replaced my winter air in my tires with summer air and its fixed!

 

Thanks for all the replies. Considering I know very little about engine repairs, the fine nuances are hard for me to wrap my head around a bit. So unfortunately I have to rely heavily on the dealer for their assessment (ughhh). I was hoping to go in with some of the more likely causes, but I guess with a job like a head gasket repair, it really could be a million things, anywhere between a huge screwup or a small mistake like a loose hose. Hopefully whatever the case may be, I wont be charged for anything.

Im really regretting going to the dealership

 

The gasket cracked when my radiator cap blew off on the highway from a coolant replacement in which the freaking technician didn't replace the cap correctly. After 10 minutes first taking it on the highway (never noticed it because I was in college and didn't really have to drive it that much) the cap blew off, but it was months later so there was no way I could fault the shop even though I not once touched the cap.