General Tech Revisit the PCV—Some Examples

[KVH]

I keep reading the posts on the subject of PCVs, and the problems and issues. I’m just not understanding the issue or the intended technology. Let me begin by mentioning 3 TR4A setups I have. These are not my setups—they are as acquired. My interest stems from crazy oil consumption I had on two of the cars, as further explained below:

1) Vehicle 1: No draft tube; PCV; non-vented oil cap—this setup, in my opinion, caused excessive oil consumption. I seem to have at least partially resolved the problem by replacing a cracked diaphragm in the PCV valve. But I’ll have to closely watch this, as I am skeptical based on prior posts on this Forum that much oil consumption could come solely from a cracked PCV diaphragm.

2) Vehicle 2: No draft tube; PCV; vented oil cap. This vehicle runs perfect. Oil consumption seems slightly excessive, though I need to watch it more thoroughly.

3) Vehicle 3: Draft tube; PCV; vented oil cap—looks like the cap came with the HRG valve cover. This vehicle runs fine, and I guess the vented cap makes sense, but having both a PCV valve and draft tube seems superfluous. Any harm leaving it that way?

I’d sure welcome any thoughts or observations.

 

[bammons]

Watching this. Waiting on parts (BO) to try to remedy mine. Bruce

 

[Sarastro]

Have you done a compression test and ruled out simple engine wear as the cause of the oil consumption?

For vehicle #1, check the diaphragm inside the oil cap. It may have a small hole, maybe 1/8" diameter, for a vent. (Mine does.) If not, you can easily drill one.

 

[RJS]

I am a purist and did all I could to make the OEM PCV work correctly. However, despite years of struggling with it and buying used PCVs off eBay and/or replacing the diaphragms/springs inside - I would still get pressure in the motor and it never idled properly. I understand the idle issue is from the fact that the PCV by designed is a controlled/variable vacuum leak into the intake manifold (post carburetors).

I ultimately resorted to this set up

• 1/2" ID heater hose off valve cover, over/between the carbs and venting down by the road. I cut a 45 degree angle on the end so it pulls a vacuum
• Original vented oil cap
• No road draft tube

Would consider better options but, right now this seems to work best. Motor pressure appears to be vented and idle is rock solid

Bob

 

[KVH]

Have you done a compression test and ruled out simple engine wear as the cause of the oil consumption?

For vehicle #1, check the diaphragm inside the oil cap. It may have a small hole, maybe 1/8" diameter, for a vent. (Mine does.) If not, you can easily drill one.

Engine is new. Compression Okay. Could be better. About 160 across all 4. No hole in oil cap, but gasket in cap seems almost homemade. Flimsy. Ratty thin cork.

 

[KVH]

I am a purist and did all I could to make the OEM PCV work correctly. However, despite years of struggling with it and buying used PCVs off eBay and/or replacing the diaphragms/springs inside - I would still get pressure in the motor and it never idled properly. I understand the idle issue is from the fact that the PCV by designed is a controlled/variable vacuum leak into the intake manifold (post carburetors).

I ultimately resorted to this set up

• 1/2" ID heater hose off valve cover, over/between the carbs and venting down by the road. I cut a 45 degree angle on the end so it pulls a vacuum
• Original vented oil cap
• No road draft tube

Would consider better options but, right now this seems to work best. Motor pressure appears to be vented and idle is rock solid

Bob

That is exactly 100 % what my mechanic keeps telling me to do.