195 thermostat?
I am having a plug fouling problem with my '67 L79 that has been recently rebuilt. I have gone through the Holley carb and it has the 65 jets and a 6.5 power valve that I am sure is not leaking. When I got the engine back from the rebuilder, it had a 160 thermostat and AC44R plugs. I have checked the float level several times, and have replaced the plugs twice; the first time with Denso W14U's and the second time with AC45R's. I also replaced the 160 thermostat with a 180. This helped a lot, and I finshed last summer with no problems (or so I thought). I got back to Minnesota this spring, and have started noticing a slight stumble on mild acceleration. I pulled the Denso plugs and put in the AC45R's. Lo and behold, the Densos were a little fouled. The new AC45R's helped a bunch, but every once in a while, I get the slight stumble on accelaration. Before tearing into the carb or changing plugs again, I am wondering if I should change the thermostat to a 195. I am located in North-Central Minnesota where it hardly ever gets inti the 80's, much less anything more (plus, since it is a non-A/C car, I don't drive it on hot days). If I remember the specs correctly, 1967's in California came with 195 thermostats. My car hardly ever shows over the mark on the gauge that is half way between 100 and 210 (which I believe to be 155). I have verified these tempuratures with a laser thermometer and it is right on. I am also thinking of changing out the jets for 63's. The car runs fine (except for the occasional stumble), and starts immediately with just a twist of the key, even after sitting several days. With the problems I've had when it had a 160 thermostat, I am leaning towards a 195. Anyone have an optinion on this?
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Re: 195 thermostat?
Dennis-----
I don't think that a 195 degree thermostat is going to do anything for you. I don't recommend the use of a 160 degree thermostat, either, as I've said many times before. Your car was originally equipped with a 180 and that's what I recommend (even for C2 and C3 but not C4 cars originally equipped with a 195).
On the other hand, changing a thermostat is relatively easy and they don't cost very much. So, if you want to try it as an experiment, go ahead. I'm betting it won't make any significant change as far as your fouling goes.In Appreciation of John Hinckley -
Re: 195 thermostat?
Dennis I have a original owner 1968 L79 that has the original engine which has not been rebuilt. I have not put a lot of miles on it in the last 25 years, but I do drive it. On 8-18-1986 I installed Champion J12Y spark plugs, the mileage was 78766. Today the mileage is 97107 and it still runs great on the Champion spark plugs I installed in 1986. It starts very quick. I have 180 thermostat. Have used a Holley spreadbore 650 double pumper since about 1974. Have not inspected the plugs since they were installed in 86. My 68's intake exhaust crossover is plugged and the heat riser is wired open.Last edited by Jim T.; July 2, 2013, 08:20 AM.Comment
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Re: 195 thermostat?
Dennis,
A few things come to mind for you to think about. Could the fuel be boiling in the accelerator pump, how much ethonal in the gas where you live. You may want to wire the heat riser valve open and see if that helps some, I agree with Joe that a 195* thermostat will not solve the issues you report.
The next thing is the metering block/metering plate on the Holley (primary and secondary), these carburetors need a good flat gasket seal and if vacuum finds fuel or air because of a poor gasket seal you will experience problems like you report. The stock Holley jets etc. will work perfect for your L-79, the secondary metering plate should be stamped with a #22. Also, the gasket seal between the throttle body and main body can cause problems, all these surfaces need to be flat.
Double check the usual things first like dwell and timing as well as making sure the spark plugs are clean so you can find the real problem. You can carefully clean the plug tips and porcelain in a glassbeader just be sure to blow out the glassbeads very good and cover the plug with some heater hose etc.
Verify the correct vacuum advance is working on the distributor, it should be a #236 vacuum control, your L-79 should make approx 13-14" vacuum at 750RPM idle and this control should be pulled full at 8"vacuum and provide 15*additional idle timing. Idle timing should be approx. 25* (10* initial plus 15* V/A), all this assumes the correct L-79 camshaft has been installed.Comment
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Re: 195 thermostat?
Post a picture of the fouled plugs- are they gas fouled or oil fouled or is it weak ignition?Comment
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Re: 195 thermostat?
I wish it were that simple. Here in Minnesota, the street rodders have worked with the legislature and non-oxygenated (no
alcohol) gas is almost universally available. I don't think it's a problem, because I use gas from the same sources in my
'68 base motor convertible and my stock '51 Ford with no problem. I want to thank all who have responded to this thread,
partially for the specific suggestions, but more for making me look a little harder at the problem. After thinking about
it, the 195 thermostat deal is just my way of looking for an easy way out. (It gets real old removing the spark plug
shielding and changing plugs on one of these.)
Here's the story. I had this engine rebuilt by a supposed pro about 6 years ago. I got dyno sheets with it that showed it
produced 336 HP. I was pretty satisfied with this until I got around to driving the car. The first problem is that the
engine was built real "tight". When I first got it, it wouldn't idle for more that a minute until the temperature started
to climb. After about 800 miles, that problem went away. Then I had serious plug fouling problems. With help from the
board, I realized that the 160 thermostat and AC44R plugs were causing a problem. I changed to AC45R's and a 180
thermostat and things got a lot better. It was running rich, however, so I decided to get into the carb, which was a
replacement 4160 I had purchased about 15 years ago, but had less than 5000 miles on it. After many weeks of changing this
and that, I found 3 problems. The prinmary throttle blades were installed upside down; the original 65 marked jets had been
drilled out, and the primary float level was set way low to make up for the drilled out jets. I fixed all of this and
installed new #65 jets and a new 6.5 power valve. Just for insurance, I bought a 2" thick granite surface plate, and spent
several hours making sure all of the mating surfaces were dead flat. I rebuilt the carb using all genuine Holley parts, installed the carb and new plugs (the Denso W14U's) last summer, and drove the car the rest of the year with no problems. I also should tell you the engine was built with 9.5 pistons and a Comp Cams XE-262 cam. As I said above, the engine starts immediately when I hit the key and runs strong up to 6200-6300 RPM (Which is as far as I care to turn it). The other problem that I have with the engine is that the rebuilder must have installed a Hi-Pressure/Hi-Volume pump, because the only time the Oil Pressure gauge is when the car is full hot at idle.
When I came back to Minnesota about a month ago, I took the car out of storage, and the occasional stumble problem reared it's ugly head. At first I thought it might be the 6 month old gas in the car, but after I filled it with non-oxygenated premium about a week ago the problem didn't go away. I changed plugs a couple of days ago (to AC45R's), and things got better, but it still has the occasional stumble. The timing, dwell, and vacuum advance are right on as far as I can see. Thought that because of the nature of the problem, it might be a power valve problem, but I tried a couple of different ones with no improvement, so I am back to a new 6.5 with a new gasket.
Someone asked whether the plugs look gas-fouled or oil-fouled; I think they look oil-fouled, and that the constant rich condition since the rebuild may have washed down the cylinder walls. I will take some pictures of the plugs to post when I get back to my shop. I think I may be screwed here. It seems to want to use about a quart of oil every 2 tanks of gas, and the mileage around town is about 8 MPG. I went on a 150 mile trip last fall and got 14 MPG As I said earlier, the car runs cool all of the time. The laser thermometer shows 176 at the thermostat housing and less in the radiator, which temperatures are in line with the dash gauge.
At this point, I suspect that there is a problem deep in the carburetor, so I have gotten another Holley to swap in. Wish me luck.Comment
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Re: 195 thermostat?
Dennis,
Thanks for posting the complete story about your engine because it really helps when making suggestions on possible cures.
IMO, after reading your post I would start by checking with the engine builder about exactly what oil pump is in the engine. If it's a high volume/high pressure pump I would change it back to a stock GM 45psi relief pump. It's possible there is so much oil/air up inside the engine the PCV is pulling some oil from the crankcase. Also, the oil thrown on the cylinder walls may be to much for the rings to wipe so that may be something to think about. You could also have so much oil up stairs that it's passing the valve guides. If you ever decide to change the pump be careful what pump you buy because the Melling pump makes to much pressure but they say the spring can be changed to a 49psi spring they sell. If you have the original pump reuse it after inspecting the internals.
Do you have the stock breathing PCV on the engine? I believe the comp 262 camshaft makes approx 10" vacuum at 900-950 RPM so make sure the vacuum advance control is the #236 or equal.
Are you running a 3810 Holley service carburetor on the engine? Make sure the accelerator pump is adjusted so .015 clearance with throttle shaft wide open. Double check the check valve inside the accelerator pump to be sure the check ball only has .013-.015 so it seats right away when the throttle is moved, that will cause hesitation. I use a wire tie like what's on a loaf of bread, they are usually about .015. Make sure the squirter check valve is in place under the squirters because the pump will fill up with air instead of gas.Comment
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Re: 195 thermostat?
"IMO, after reading your post I would start by checking with the engine builder about exactly what oil pump is in the engine". Unfortunately, the engine builder (who had a very good reputation) died from stomach cancer half way through the rebuild, and it was finished by his son. Tim, thank you for the response; do you think the oil pump may be a part of the problem? My problem is that I am 71 years old and cannot get down on the floor any more because of my arthritis. I really wouldn't mind the gas mileage and oil consumption problems if I could get rid of the stumble (as long as they don't get any worse). I do have a (relatively) young guy here that I have a good relationship that would probably change the oil pump for me if it's that important. I am still going to replace the carb, since I have one.Comment
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Re: 195 thermostat?
I think you need to focus on the oil fouled plugs and high oil consumption.Comment
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Re: 195 thermostat?
I think you're right (which lead me to post that I am probably "screwed". It puffs out some blue smoke at initial start-uo, but seems fine afterward, which sounds like valve guides This is supposed to be a top level rebuilt). As of now, I'm waiting to replace the carb.Comment
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Re: 195 thermostat?
Dennis,
If it were mine I would seriously think about changing the oil pump if it's a HP/HV pump but that's just my opinion, you need to find out what pump is in there first. Before doing anything to the engine double check the accelerator pump adjustments I mentioned in my post, you may eliminate the stumble because I think it's a different problem.
I once owned a 1968 Corvette that I had bored .030 and rebuilt that had the same problem as your engine. I tried everything including re-ringing the engine and never could find anything wrong or fix the problem. I had to change the plugs very often. The engine had a HP/HV GM pump that I now suspect was the core of the problem. All eight plugs oil fouled, and I think the valve cover baffles were overcome by the volume of oil air forth and the PCV pulled that vapor into the engine.Comment
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Re: 195 thermostat?
While I don't think a high pressure oil pump is a good idea for an L79/350 HP, I doubt it would cause excessive oil consumption. After all, the same high pressure pump is used for all L76/365 HP engines and these engines didn't have excessive oil consumption problems.
If any fresh rebuild engine requires more than about 15 seconds of running to break in with modern piston rings, there is something seriously wrong with the bore finish or?? If an engine builder tells you it will take hundreds of miles to seat the rings, find a different builder because he has no clue. Those stories go back several decades, to the days of rough hone and chrome rings.
If your engine builder does not have/use an automatic feed precision hone, find another builder. Period!
Spend a few extra bucks and insist the block be honed with deck plates installed.Comment
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Re: 195 thermostat?
Mike,
But didn't those solid lifter engines use a standard volume oil pump and edge orifice lifters.Comment
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Re: 195 thermostat?
Timothy,
I don't remember on the lifter design (side orifice/piddle) but all mechanical lifter engines from mid 63 through 65 used the high pressure oil pump.
I don't remember the exact oil mileage on my new 365 HP 64 coupe but I do remember that it didn't use more than about a quart in 1,000 miles. There was never burnt oil coming out of the exhaust, even with less than 10 miles on the car. And that was with almost 50 year old technology.
Modern honing processes and much improved piston ring design should pretty much completely eliminate break in.
The old "rough em up so the rings seat" theory and "it's tight because we just rebuilt it", died with the disappearance of the dinosaur.Comment
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