• Hey Guest!
    British Car Forum has been supporting enthusiasts for over 25 years by providing a great place to share our love for British cars. You can support our efforts by upgrading your membership for less than the dues of most car clubs. There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Upgraded members don't see this banner, nor will you see the Google ads that appear on the site.)
  • When posting a classified ad, you MUST select a prefix from the drop-down next to the subject line. If you don't you will get an error and your ad will not be posted!
Tips
Tips

Carbon: Good vs. Bad

Share this page

RJS

RJS

Jedi Warrior
Country flag
Offline
Hi,

My engine was rebuilt about 7,500 miles ago. About 2,000 miles ago it starting producing some excess blow-by (evidenced by crankcase pressurization). I can solve this by simply removing the PCV and venting to the atmosphere.

However, I am still perplexed by what "changed" to cause this. Then I started thinking that a season or two ago I started to run a bottle of Techron through the gas tank once or twice a season.

Is it just possible the Techron removed some beneficial carbon build-up which was helping to seal the rings? I have read about this here or there but, has anyone actually seen evidence to support this theory?

Bob
 
Hi Bob. I personally don't think that with that few miles some Techron should have made <span style="text-decoration: underline">any</span> difference at all. The blow-by usually indicates issues that, sorry to say, are usually internal to the engine from what I understand. I hate to say it, but I'm guessing the rings are not seated properly for reasons totally removed from any gas additive.

Sorry. Maybe the guys with more experience will have some ideas for you that are less disappointing.
 
I wouldn't think that techron would do that in a motor that fresh, you'd have to build up a lot of carbon in a short time for that.
Is your motor down on power, burning appreciable oil, oil in the water possibly...
 
Thanks guys,

Not sure it is that dire. I have been noodling on this for a while and this idea (of cleaning out "good" carbon) popped into my head as a possible cause. The car is stored for the winter now and will probably do a leak down test and inspect cylinders with a bore-o-scope this spring.

The engine runs perfect in every other way. It has 172-175psi compression across all four cylinders and pulls a healthy 20" Hg vacuum. It starts, runs, idles great. Really nice power and excellent throttle response. I get ~21mpg. Plugs are dry and coolant is clean.

The only other things I suspect are:
1. bore wash from running an overly rich carb mixture for about 2000 miles
2. stuck rings caused by carbon build-up as a result of 1. above (this is why I tried the Techron in the first place)
3. my mechanic removed and "re-planed" the cylinder head a couple of years ago. I have no idea how much he took off the head but, perhaps it increased the compression ratio resulting in increased blow-by volume.

Anyone have additional thoughts on these three possibilities?

Cheers

Bob
 
When you said PCV, that became my #1 suspect. Some of those things clog up.
Even the hoses that are attached to it can get emulsified obstructions.
 
Back
Top