I'm getting ready to replace the valve cover gaskets on my 1998 Tacoma 3.4L, and I've been reading through different threads, tutorials, and watching videos. In almost every instance, it looks like the leak is caused by loose valve cover bolts, and I've read reports from several people claiming that the job only fixes the leak for a couple of years and the bolt loosen up again. I don't think I've seen anyone replace the valve cover bolts when doing this job.

This leads me to wonder, are the original bolt stretching, causing them to loosen prematurely, even if torqued to factory specs? Any thoughts on that theory?

OEM bolts aren't very expensive, so it wouldn't break the bank to buy new ones. That being said, I'd rather save the money if it won't help the situation.

 

It's not the bolt stretching, it's the squishy rubber doughnut seal underneath it. It's intended to limit the amount of pressure put onto the valve cover by the bolt (they break fairly easily, I think). So the bolt pushes on a wide cupped washer, the washer presses onto a rubber seal/doughnut, and that pushes into the valve cover.

As those rubber seals age they start to lose their spring, and it loosens up, and can allow leaking from the main gasket. If you tighten it up, that can help for a while, but they still continue to collapse and mash flat.

It's one of those things where the OEM parts last 10 years, the aftermarket parts cost half as much but only lasts 2 years, not really saving you much.



On mine, it had started leaking at around 190K miles, and I did try gently tightening all the bolts I could reach. Some of them were quite loose. And the oil leaks slowed for a few months, then came back as strong as ever. Titghtening the second time around didn't seem to help much, so I just redid it all.

 

The grommets from a 96 3.4 after 282,000 miles...
(pay no attention to the bolt in the pic, it's for the plastic wiring cover)

Compared to above, you can see what Jomoka is talking about.

I also measured the new vs old valve cover gaskets. The old one was also compressed to a shorter height.

Re-using the old bolts has been no worries, but with a torque spec of something like 6nm or 53 inch lbs I didn't expect any.
There is a pattern when you are tightening them.
When you tighten those bolts stick to the spec, have seen people manage to break the valve cover with too much torque.

Note: Toyota valve cover grommets were shaped differently than the ones that came with my Yotashop headgasket set. When I pulled it apart for a head gasket job with 30,000 miles on the valve cover/toyota parts job it was dry. I used the yotashop grommets supplied, those lasted less than a year.

Toyota in back, Yotashop (brand unknown) in front with about 6,000 miles on them:

 

Guys, thank you for the responses. I won't worry about new bolts then, but I will make sure to replace the cupped, rubber seals/grommets.

Once again, the responses are much appreciated.