Sounds to me like your bypass is partially kinked. and you are not running a heater core. do not just plug these off the water needs ALOT of flow. around and aroundand if the problem persists connect a 5/8" hose to the to the bottom or right side of the rad. Like most BBC's have. Im gonna guess your not bypassing enough
It has a by pass hose and has a heater also. The hoses are all new. I will check them again for sure. Thanks M[ quote=zbuickman;3597181]Sounds to me like your bypass is partially kinked. and you are not running a heater core. do not just plug these off the water needs ALOT of flow. around and aroundand if the problem persists connect a 5/8" hose to the to the bottom or right side of the rad. Like most BBC's have. Im gonna guess your not bypassing enough[/quote]
Does it have stock pulleys? Oem pulleys have a larger pulley on crank to overdrive the waterpump and alt.
Seems like a mystery.. I think I would say screw it and drive the shit out of it and not worry about it until either something gives, or NOTHING gives.... But I am just reckless that way...
I have had the same thing on a bbc and pontiac 421. In my case, it's the thermostat opening and closing. In temperate weather, it's not too noticeable. However, New Years Day, we went on a long cruise along the coast. The air temp was in the 30's and the temp would jump between 215 and 190. After the air temp warmed up, it quit flutuating.
Might try getting a really crappy temp gage, and then ignore it. If the engine isn't boiling over, it's not a problem!
SBC, 383, Hi-Flow water pump, Walker Cobra Z radiator and a SPAL 16" puller fan. New Classic Instrument electric gauge set put in awhile back with a dedicated ground, and temp would go to 180 for a few minutes, then on up to 200 and 210 and maybe get to 220 at idle, and turning the heater on would bring it down to about 185 - 190. Going over it with a temp gun gave a high reading of 175 on a freeze-out plug under the alternator. Was in the 108 - 142 range about everywhere else......radiator and heater hoses, sender, water pump, radiator etc. I then hooked up a cheap mechanical gauge and couldn't get it to go over 190 when idling for 15 - 20 minutes in 80 - 85 degree air temp, with the heater off, . The temp gun reading corresponded with the mechanical gauge as it climbed and I got the same readings as before with the temp gun, about 176 at the freeze-out plug. So to double-check it I boiled some water with the cheap mechanical gauge and our Taylor deep-fry thermometer. The mechanical was 20 degrees slower climbing all the way to 206, then both were the same at 206 degrees. They stayed the same while cooling down. Thinking it was out of calibration I spoke with a Classic tech rep. He suggested I run 108 ohms to two terminals, and if the gauge was calibrated it would read 195, or right in the middle of the needle sweep. The test yeilded a reading of 220-225, so Classic sent me a new gauge and sender. Hooked up new gauge and sender. New gauge reads about the same as the old one, with the outside air temperature about 70 degrees. And the sender leaks around the threads because of no pipe thread compound or teflon as per the instructions. Next I ran a 16 gauge wire from the sender to the new gauge in case there was a problem inside the wiring harness, and the gauge reading stayed the same. So right now I'm having a cold beer and playing with the baby's mother while the engine cools down. Then I'll go out and put the old sender back in the intake with a bit of thread sealant at the top of the threads, then check for continuity between the sender and manifold. The old sender seemed to screw in a bit easier and a bit further. And, the recommended torque of 20 inch pounds is a pipedream. A ton of rods & customs run Classic Instruments gauges, so I'm having trouble believing that the two electric gauges read the same and are both bad. But because the temp gun and the mechanical gauge read about the same, and the mechanical gauge and the frying thermometer are the same ultimately at boiling, it's 2 to 1 in favor of the cheap mechanical gauge being correct, but it doesn't fit the opening. I sure hate to drive it with the temp reading 25-30 degrees too high, but it's only about 64 degrees outside now, and with the cooling stuff I'm running on a mild stroker it shouldn't overheat. I guess I can buy another mechanical gauge that fits and see what it reads, but I'd really like the electric one to work. Any help will be appreciated. Thanks, Unkledaddy I SOLVED MY PROBLEM ENTIRELY BY REPLACING THE HI-FLOW WATER PUMP WITH A OEM ONE.
All of my big blocks always ran cool, never over 190 even in traffic. With your temperature instantly fluctuating like it is, I agree with the gage issue. I always ran pure mechanical gages in my cars, the only thing that was powered was the light so I could see it at night. Go grab a cheap mechanical gage, hook it up and go for a ride. Any BBC I had weren't prone to air entrapment either. Bob
This is bugging me, wasn't there a bypass restriction sleeve that you used to slow the water hammer effect when the pump bypassed to the intake (where the gauge sender is) they put in according to whether it was an AC car or not. Way back it seems like I ran into a deal like this. A higher flow pump was installed and everytime it bypassed hard it would hammer the sender and make the idiot light come on making you think you were overheated. I was doing dealership work, but this was a friend of mine who had the trouble with a 396/402 in a '71 Chevelle. Any recollection?
You mentioned in your first post that you replaced the head gaskets. Do you know what brand of gasket you used, and the part number?
They are Felpro and came in a head set. I do not know the part number but can get it toninght. Thanks M
Man...any help with this one would be great. I have no idea what this is about, so details please.......THANKS M
My only statement to this is that the problem was there with a stock pump, I put a new high flow pump on to try to help but iy did nothing for the issue. I do have the stock pump still and can put it back on. It was a rebuilt unit and has a few thousand miles on it.....maybe I will just buy another stock pump and put that on. Let me try a few of these other ideas first and then I will go with a new pump again. THANKS SO MUCH FOR YOUR HELP. M
My sending unit is screwed into the intake manifold and the mechanical gauge temperature probe on the sending unit is a lot longer than on the electric one. I considered that with a high-flow pump and short probe there might be cavitation and a steam pocket issue.
Get a high volume or heavy duty thermastat or drill a small hole in the one you have. Todays thermastats are made for FI, and don't work well carbs. Took me three thermastats before I figured that out.
The water flows the OTHER way. Into the engine at the bottom, out to the radiator at the TOP. My guess is like one of the others, BOTTOM radiator hose collapsing. Since you have the "high flow aluminum" water pump you absolutely need the spring in the hose. With the thermostat OUT the flow is so high that no heat is drawn from the metal to the water and the gauge shows low reading. Put the spring in the bottom hose.
Sounds good, I will do this tomorrow and give a report. Thanks a million. PS, I did run straight 12 v to the dissy , no change. I did put a new thermostat with 1/8 hole in it, no change. Thanks M
I had a very similar problem on my wifes Tahoe with a 350. The problem was due to a plugged bypass hose. Brian
Chit,,, I thought all 1st gen SBC had internal bypass.... = no hose? No doubt the internal bypass could get plugged, and I am more than willint to accept correction if some SBC have external bypass, I have just never seen one that I paid any mind...
OK, WOW........I believe we have a winner. I put another new bottom radiator hose on the car and this time got one with the spring in it, even though the hose from the factory was not that way. I took the truck for a short drive 2 times now and no issues. The issues normally came up pretty fast so, I am not 100% sure that it is fixed, but believe that it is. All I have to say is THANKS TO ALL THAT HELPED. I was completely lost and it was getting very old just throwing 100.00 dollar bills at the problem and having the truck laugh at me. THANKS....AGAIN, to ALL
OK, new update........problems came back and so I drove it to a local engine rebuilder. He gave me some of those washers that you put in where the thermostat goes. That made the overheating go away and the fast temp swings, but it runs too cold now. I was told by unkledaddyto get the high flow pump off and I believe that I will try that next. I have ordered a stock rebuilt pump and it will be here next week. Parts stores in my area have nothing for old cars. Thanks ,,,,,,,,,,,,,,,,will let you guys know what happens.
The one thing that sticks out, to me, is that you said it was running fine...replaced the head gaskets...and now have troubles. That's why I asked about the part number...I wondered if perhaps you had used Gen V-specific gaskets by accident. Was it ever running cool in the truck (before you did the work to it), or, was it fine in the car but never in the truck?
fine in the car and never in the truck. I do not have the part number for the head gaskets, so the only option there would be to rip it open again? THANKS for all the help
If you ordered the set by application..i.e. 1971 Chevrolet 402-powered "whatever', chances are it's fine.
WELL, I can not believe it but this was the trick....stock water pump solved all the issues...........THANKS UNKLDADDY
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