OK, this will take a little time to explain but here goes. The engine is a 71 Chev 402 CID big block. I pulled it from a running car and I drove it before installing it in 48 Chev truck. No issues at all. Problem is it runs hot, but not just the normal way. When you drive it the temp goes up to 190 and stays there for a while, then it will send the temp to 250 and back to 190 all in less than 5 seconds. I ***umed that it was not a real temp so I have installed a second temp gauge in the truck. One in the intake and one in drivers head. Same readings. It is obvious that the temp going back to 190 is from the thermostat opening and letting in the cooler water so I have replaced the thermostat. (4 times) No change. Then I started replacing other stuff to see what I can find. below is a list of the new stuff that has been replaced after the heating issue started. NEW water pump High flow aluminum (yes it is the right rotation) new fan blade (yes it is on the right direction) New bad boy aluminum radiator. Fab shroud (no fan clutch) No room for one. New temp gauge New radiator cap Over flow tank Changes that were made to the engine between the time that it was running good and now. While it was out of the car, I changed it to a 4 speed, was auto Added HEI dissy to the engine. General clean up and replaced head gaskets and intake gaskets. Pretty sure they can not go on wrong, I have changed the timing 10 times. Everything from setting it by the book to setting it by ear the old school way. Truck seems to run OK but it just scares me to drive it long distances this way. I also have added a Vintage heat and air unit to this truck, however the heat happens with the AC on or off. I removed the thermostat completely for a test and the truck will not get hot at all. It will run at about 100 deg. I would like some heat to be able to run the 1000.00 heater. I am sure that I have left out something so please ask anything and I will do my best to answer. Questions that I still have that I have yet to answer are ....Is there something wrong with the new dissy so that the heat is caused by a timing issue? The old one was a points type and I do not have it or I would put it back it to test. The HEI is a new one but could have something wrong with it?? Seems unlikely. Is there a possibility that I could have 4 bad thermostats in a row? If not then why is it that I can not make it get hot or even warm running without one. Running 160 and 180 thermostats, still runs 190 or above. I have had a few "mechanics" look at this and take them for a ride. They all say the same thing. "I have never seen anything like that before" Now as you can tell, I have done "everything" and still can not find the issue. Any and all help would be appreciated, but please do not send info like "remove the Chev and replace it with a flathead" THANKS M
Does it do that sitting in the driveway & idling?? Random thoughts..do you have the byp*** hose in place from the intake to the water pump? How bout the lower hose spring, any chance it's partially collapsing? When the water goes 250 does the engine smell hot or seem pingy?? Basically wondering if it's a true reading. Should be acting like dog **** at that temp good luck
The temperature of the coolant cannot change that fast, so it has to be a gage problem...if it's an electric gage, look for loose wires, grounds, voltage spikes, bad instrument cluster ground, etc
Also have you tried the trick of drilling a small (1/16") hole in the thermostat? If there's a bubble that's causing the thermostat to open suddenly, this might help. Still, 5 seconds is a short time! if it were a minute or two, I would think this might help
Both gauges are hooked to the engine at the same time. They are both mechanical and new. Both from different manufactures and both read the same. The one near the thermostat is a little faster to swing and I believe that is because it is closer to the cooler water coming in. The hoses are all new and I have checked to make sure they are not collapsing and the byp*** hose is new and in place also. I also thought that it could not be a real temp, but I believe now that it is. It seems to run pretty good even when this hot but remember it is only that hot for seconds and this is a low compression smog motor. I can not make it ping or spark know no matter where the timing is set. Keep it coming and THANKS
Oh you can make a low compression smog motor ping at 250. Trust me. If the coolant is actually 250, then the engine is actually that hot. The coolant only absorbs heat, so it's the last thing to see temperature spike. Even momentarily I'd expect burning oil/paint/plastic smells and weird manners Have you verified the balancer ring hasn't slipped and the timing is true? That HEI hasn't stuck one of the advance mechanisms?
I have not checked the balancer....good thought, thanks. I have set the timing by ear also. That should eliminate and issues with the timing marks, but I will check this for sure. The water pump is running the right direction and I did check that. In fact the pump was changed because of this issue but made no change. AS for the ping, the temp is only at 250 for seconds, so it could be running bad and I just do not know it.
check the thermostat houseing make sure it does not have anything thats interfearing with the thermostat. If thats not it get a thermostat houseing that you can bleed air out of you could have a air pockett in the motor or heater core the thermostat could have trapped hope this helps
THANKS....the temp unit that is installed in the intake is the one that swings the wildest. The one that is in the head swings wild also but not quite as fast. Yes it seems that all of the stock stuff was good and the new stuff has been an exercise in how to spend money that I do not have. I do believe that the temp is for real, especially since 2 mechanical gauges hooked to the engine at the same time are reading the same thing. Both gauges have also been put into my Model A for testing and work perfectly? STRANGE I KNOW, but I am still missing something. THANKS,
I forgot to mention that I have worked hard to make sure there is no air inthe system. I believe it is out, but not 100%. The housing thing is a good idea. THANKS. M
Try the hole in the thermostat trick, just to see what happens, it will only cost you a gasket to do it.
If you're looking for data points I have an off topic vehicle with a SBC, aluminum radiator, and a digital gauge that's accurate to a degree. You can literally tell outside temperature if the car's been shut off long enough. There's been a couple motors, water pumps, and thermostats in the car. You can watch the thermostat regulate flow on the gauge like no car I've ever seen. There's about 7 degrees variation in use, starts about 2 before setpoint and ends 5 over. It's freakish how consistent all those thermostats have been. Moral of this story...this can't be attributed to sender placement. Are you really sure those head gaskets are sealed up? Probably wouldn't hurt to throw in a silicate pellet, GM does it on everything that gets head gaskets or a motor at a dealer. good luck
Do not know what a silicate pellet is, but ***ume that I can get it at a parts store. Is it ok with the aluminum radiator? I have used the thermostat with the 1/8 hole drilled in it, no change. I agree that it can not be the placement of the sender. They have been in the same place for many years and if this was a problem it would be on many cars. I am not loosing water (coolant) so I ***ume that the head gasket are not leaking. The swings that I am seeing are big and fast. I ahve never seen anything like this before.
Have you checked to see if your getting combustion pressure (bubbles in the coolant)by looking in the radiator fill while the engine is running? Might try a compression test both hot and cold to see if there is a variation. Frank
Those sealer pellets are kind of controversial but probably a million plus vehicles on the road with em. Every now and then they get 5 years old and re-ac***ulate into a jellyfish that's gotta be flushed out of the heater core, but I've never seen them do any worse. GMs newest gasket-less designs actually rely on them. Mine come from a dealer tech friend but if you call a napa or other intelligent parts store and describe it, they've probably got something real close or even the actual delco product. Couple bucks a pill. Hate to say it but I'm starting to wonder if you've got a hairline cracked head or valve seat something else. good luck
That's what I was wondering too, a cracked or leaking exhaust seat insert or a leak between two cylinders on the head gasket. I have used those pellets on a lot of things, especially stuff with non-coated head gaskets. You should be able to get them anywhere. BarsLeaks pills are the same. I even put an raw egg in the radiator once to stop a pinhole leak from a collision with a "love bug" in the radiator. 2 years and holding. It wasn't much of a leak though. Something else on BBCs is a restrictor in the byp*** that equalizes pressure. There were different ones for different pumps. Too long ago to remember, but maybe it will jog someones memory.
That it runs cold and consistent w/o the thermostat is a clue. Have the thermostats all been the same brand? I'd take one and cut the works out of it so that there is only the flange left with the flared hole in the center and install that in the manifold. The restriction may bring the temp up a little. If not up far enough, make a washer with a smaller hole and keep going smaller until it runs @ 160 and see if the wild swings in temperature still happen. Also, pick up a cheap infrared temp gun at Harbor Freight for $15 or so and use it to diagnose hot spots on the engine, radiator, etc. and compare against your gages.
Out of curiousity, what's it do for temperature if you stand on it for a gear or two when it's running 180?
Aint saying this is the fix but its worth a look. I have a 72 blazer that i put a 468 in . I had been having a similar problem also , only it would peg the temp gauge then fall back. After doing some research and ALOT of trial and error , this is what i came up with . I had a week alternator, very week . I know it doesnt sound right BUT , those hei's like the correct flow , right around 12-14 amps. If something has happened in the regulator where it is not giving the dizzy the proper amps it can misfire a bit and cause the heat up . Believe it or not , thats exactly what mine was doing , i swapped out a bunch of thermostats , drilled holes , everything . Noticed at high rpms i was getting some bad popping and misfires. But not till i p***ed 4 grand. The dizzy was runnin out of juice up there and apparently even at low rpms was throwing it off a bit and causing it to over heat. Replaced the alternator and it has never heated up since , even had it out rompin the **** out of it on an old mud road and could not get it above 210.
The more i think about it , it all started when you dropped the hei in , That distributor is not getting enough juice causing the temp spike. Dont know what your set up is , but my fix was a 73 to 87 truck alternator , wired the main out put big red wire straight to the battery , and the 2 spade wires to excite the regulator , i wired both of those directly to a 12 volt switch to start the charging when i start it . You can wire them to any 12 volt wire that becomes hot with the ignition or put it on a toggle like i did. There is a good chance if you are running the original externaly regulated charging system that it isnt sending the right amps to the dizzy.
Also have you tried the trick of drilling a small (1/16") hole in the thermostat? If there's a bubble that's causing the thermostat to open suddenly, this might help. Still, 5 seconds is a short time! if it were a minute or two, I would think this might help <!-- / message --><!-- sig -->__________________ Pay attention to Sq....s advice. This often works well Don
seems to make no change, run it hard or easy. seems to go up more in traffic but as soon as you get and rpms at all the temp will go back down. I need to check to see if the swings come when just sitting in the driveway and not moving, but I do not know that yet?
WOW.........you know this makes a lot of sense. BIG THANK YOU. I will jump on it this week end and give a full report. I can run a temp wire direct to the battery. If it solves the issue then I will dig deeper into the wireing. THANKS AGAIN. M
Just one of those things -- but could there be something in the coolant floating around and sometimes blocking the thermostat? I know it would be something strange to be able to go through the water pump without getting chopped up, but this is getting to that point if the dizzy isn't the problem
Never say never but I do not think so. I will drain it again if the dissy turns out to be OK. THANKS and I must say you guys are great. Thanks for the help. I have lots to check now and before I wrote this I was out of options. Keep them coming and I will give a full report soon.
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