Help[ !! What happened here?

[CCCC]

I just experienced an unusual event with the engine of one of my old Chev trucks (‘71 C20/SB350) and am thinking that some of you may have had, or heard about, the same kind of thing. Before I start in to diagnose and fix the problem, I would like to benefit from your knowledge/experience.

As background and with the thought that many of you have experienced the bad outcomes of ethanol sitting in our gas tanks and fuel lines, due to a prolonged recovery from a health matter I was not able to run most of my trucks for quite a while. So, then spent a lot of time and effort – and some $ - dealing with the corrosion/particles formed due to ethanol absorbed moisture in the OE fuel tanks and collected in fuel filters and carbs, not to mention damage to fuel lines, fuel pumps, etc..

I have been moving my trucks to a new home and this was the final one – 250 mile drive from rather high elevation to desert - and all went just fine for the initial 150 miles from cool morning to mid-day 95+ degree temps. Engine running easy/quiet with excellent output (pulling a 1500 lb. trailer) – and normal amps/temp/oil pressure. Periodic stops to check the loads, hitches, tires, etc. showed zero leaks or problems. But, the fuel gauge seemed to be dropping more than expected.

After a short stop at a rest area and then running about 10 minutes at 60 mph on an interstate, the trailing partner on radio saw a sizable puff of blue smoke from under my truck which then tapered away, and also smelled something like petro burning – and I smelled the same thing. Oil pressure dropped slightly. Stopped at the first good opportunity and found plenty of oil on the pass side of engine and dripping from the frame – level on dipstick slightly below “add” and dipstick holder out of its hole in the block. Oil leak seems to be coming from the joint between oil pan and block in middle of pass side of engine. I am figuring a blown gasket there. After adding oil and trying to drive it a bit further (good oil pressure), a stop to check showed continued leaking. Hauled the whole rig home on a 40 ft. trailer.

Now – please evaluate my guesswork and/or tell me your diagnosis before I tackle the job. I think that ethanol damage had caused an opening in the diaphragm of the fuel pump and that it was pumping fuel into the crankcase and, after accumulation of fuel and heat in there, a sudden flaming or explosion caused the blowout of the dipstick holder and pan gasket – and the escaping blue smoke. Or???

Thanks in advance for any replies/advice.

[dmjlambert]

I like your guesswork, it seems like a good theory to me.

As for your Or? question, you could just have a combination of gasket leaking oil (could be somewhere besides oil pan gasket, such as valve cover gasket), and a rich condition and backfire because of crud stuck in the carburetor's needle and seat. I suppose the fuel pump would be pretty easy to remove and look at. I got mine from Autozone for about $20, it is Delphi and has lasted a couple of years so far. The only reason I changed it is because I physically damaged it, not because the diaphragm blew. Drain some your oil and see if it smells like gas.

I have heard that letting them sit makes them go bad when they are sitting with gasohol in them. I wonder if that is true. i've always used gasohol and not had problems, but mine is a daily driver. If I had one of these trucks that I mostly stored and didn't drive often, I would probably try to use non-ethanol gas in the last tank before storage, or if that was not an option at the gas station because of where you live, run the truck completely out of gas or drain it and restart it with a quart or 2 of the fancy Trufuel 4-cycle gas that you can get in Lowes or Home Depot in cans (roughly $6/quart).

[Killer Bee]

PCV valve stuck closed

[dmjlambert]

Killer Bee, would the PCV valve stuck also need to be combined with the breather tube or breather filter clogged to cause a malfunction? Just curious.

[CCCC]

Thanks for the thoughts so far. PCV valve is clear and functioning. No oil leaking from under valve rocker covers - but one visible leak/stream from top of crankcase pan running down the side. It was hot under there on the roadside yesterday and the dripping oil seemed somewhat thinner than it should have been, and oil on dipstick has some gas smell. I'm wondering if gas-thinned oil did a good enough lube job on the various bearings/surfaces while this was happening.

I now go to great lengths to keep non-ethanol fuel in all of the old Chevs/GMC now - went through a bunch of fixes on almost every one after they sat with ethanol in them. Quite vexing.

Any other thoughts out there about cause?

[Andy4639]

From your own words high elevation to desert sounds like your carburetor will need adjusting for the difference in the elevation change maybe.
Does the gas you use have something to do with it, yes.
Pulling a trailer also added to it.

[CCCC]

Originally Posted by Andy4639

From your own words high elevation to desert sounds like your carburetor will need adjusting for the difference in the elevation change maybe.
Does the gas you use have something to do with it, yes.
Pulling a trailer also added to it.

Ordinarily, I adjust idle mixture to compensate for such change in elevation - but usually do not have to adjust for air available at driving speeds. If that is needed, a change of jet size can be done. And, timing advance may need attention. However, none of the above seems at all related to the described surprise, nor does the trailer.

[BigBird05]

Take an oil sample in and have it analyzed. That will tell you if there is gas in the oil. I would change your oil anyway to be on the safe side.

[BigBird05]

In the 70's I had an engine blow up because of gas in the oil. The farmer said it wouldn't start but didn't give me the whole story. I charged the battery and changed the points. Pow!

[CCCC]

It will be a day or two before I can get this truck on the lift to work on it because another truck (69 Longhorn) is sitting in the way waiting for me to finish rebuilding the Holley 4bbl for it. I plan to drain and analyze the contents of the crank case, remove the pan and be prepared to replace the pan gasket which looks to be blown out in the middle of the pass side of the engine. As much as I am able, will try to determine if any damage has been done to the lower end by the ostensible "explosion" or due to running with motor oil diluted by gasoline. I hope the findings are pleasant because this is a really nice truck with a very solid 350. Also will change the fuel filter and replace the fuel pump before cranking it up again.

Thanks to those who posted thoughts. Actually, I am somewhat surprised that more folks here have not experienced or heard of such an issue - but maybe some have not read the thread. Thanks again.

[LockDoc]

-
I once had a problem with gas entering the crankcase and exploding in the pan. It actually killed the engine with a big puff of blue smoke, but I was only going about 20mph at the time. It started back up and I drove it to a friends house close by. It ended up I had a hole in one of the pistons and gas was getting into the crankcase through that. It actually deformed the pan between each pan bolt and I had to rebuild the engine and replace the pan. I would do a compression check first off.....

LockDoc

[RustyBucket]

Originally Posted by CCCC

remove the pan and be prepared to replace the pan gasket which looks to be blown out in the middle of the pass side of the engine.

Sounds like your "blown out" pan gasket is beyond help... but awhile back I had a bad pan rail oil leak on my Nova. A smart guy I know sealed the breather openings on the valve covers and the dipstick tube with duct tape. At the leak point he loosened 3 bolts on the pan rail and hooked a vacuum pump into one of the breather holes in a valve cover. He put a dab of RTV at the leak point on the pan rail/oil pan and it sucked the sealer into the gap. Tightened the bolts and cured my leak. Ran the car that night & busted the case on the powerglide. I've never had good no leak success changing pan gaskets in the veh. I've had 'em leak installed upside down on an engine stand.