Hey guys, feel like I've been beating my head against a wall here so I thought I'd ask for some advise. I have a 27 roadster with a 468 big block chevy in it. My friend started to build the car over 20 years ago and I just recently talked him out of it and finished it up. He built the engine, all factory GM parts except the mag, runs a holley 4 barrel that's plenty rich. Ill start at the front. It has a walker 4 core model t radiator, new flexolite electric fan with shroud spinning in the correct direction. New (supposedly high flow water pump) with bypass hose connected to manifold. 160 thermostat with 1/8 hole drilled, but am going to change to a 180 sometime today. I've tried retarding the timing, tried advancing the timing, doesn't seem to help much either. I can drive it down the road for awhile but eventually it just gets hotter and hotter. Doesn't seem to cool down at an idle either. This is my first big block, am I missing something here?? Any suggestions would be greatly helpful at this point. Thanks guys!
I had a 454 (stock) in the OFT (29 AA) in mid 70's that did same thing. Ended up trading 454 to a guy for use in his Suburban (it ran hot in the Suburban also). Put in a 327-same setup cooling wise and no issues (in OFT). Same truck but 15 years latter put in a 396 with blower and lake's style headers. Ran fine no issues. Four years latter redid style of truck and put in another 454 (no blower)-it ran hot and would not cool down as yours is doing. Put back in the 396 with blower and it ran hot. After two different radiators it ended up being the Sanderson tight tuck cast headers that were close to block putting heat back into bottom end. Seems one of the issues with some 454 is it likes to heat up. "T" style radiator may not have enough capacity to cool it.
Try setting a box fan in front of the radiator and see if that helps. Another thought,is the water pump pulley smaller than the crank pulley?,you don't want them to be the same size. HRP
You can have the water pump turning too fast, as this can flow the coolant too fast and doesn't have time to lose its heat. Also what color is your motor painted as shiny light colors don't radiate heat well. The radiator is not the only place a motor gets cooled. JW
When it gets hot I'd use a infrared thermometer to see if the radiator is getting hot all over its surface. It should be somewhat cooler near the outlet hose side, but pretty darned hot all over, If not I'd say the circulation in the radiator is poor. Those infrared guns are convenient but they rely on something called the "emissivity" of the surface so bare metal, different paints and probably a bunch of other things make them inaccurate. Still very useful for comparative readings
Thanks for the info guys, going to try a few things today and see what happens I do have the larger crank pulley smaller water pump pulley Engine is painted a medium grey, I'm going to borrow an infrared temp gun today and do some checking with that too
I wonder how many guys have solved overheating problems by slowing the pump down or restricting the flow. Think of it this way, the longer the coolant is in the radiator "cooling off", the longer the coolant is in the engine heating up. Sorry, not buying that solution and my experience has shown that it exacerbates the problem. Big block Chevy engines are a bear to keep cool, I have one and have been solving cooling issues with them for some time. The NUMBER ONE cause of most of the overheating problems I have solved has been related to the bypass between the water pump and the intake coolant passage. If it has been removed or never installed, the coolant stagnates in the heads and forms steam pockets. A small hole in your thermostat will not pass enough coolant to prevent the steam pockets from forming. These steam pockets displace a considerable amount of coolant and can puke it out, hence the need for an overflow tank. When these pockets form, they insulate the back of the combustion chamber and if allowed to grow past the micro-bubble stage, they can and usually do cause your overheating issue. On my particular set up, I had to install a degas tank similar to what you see in modern cars. This, like the stock bypass keeps coolant circulating inside the engine but also removes any air pockets that form from the engine into a separate tank. I converted to a Vintage Air front runner a while ago that deleted the stock bypass and the overheating became a serious issue, even with a 1/4" hole in the thermostat. Air/Steam does not conduct heat worth a crap in a coolant system.
Once everything is determined to be ok on the engine such as timing being correct etc.,etc., and the cars still overheats. Rule of thumb, if it is going down the road and doesn't cool it's a coolant issue. If traveling in traffic, running hot then it's an air flow issue. Just reading back on your post,stating you had a high flow water pump. You also need a high flow thermostat or use a restrictor and replace your thermostat. The middle sized restrictor solved a problem for me with a Milodon high flow pump and a Ron Davis Aluminum radiator. The middle sized restrictor also allows the heater to work,plus you never have to worry about a thermostat getting stuck.
Some picture would help us find any issues you might have. What kind of lower and upper hoses are you running? what size? You want to be running 1 3/4" lower hose and I suggest using smooth rubber hose. This flexable stainless hose on the market is very restrictive, way to restrictive for a lower hose anyways.
@ironhill Can you verify the circulation through the radiator by looking in it? If you can see the liquid move fast when the thermostat lifts, that would be a help. If it's not lifting, you'll know, but generally speaking if the upper hose starts to get hot when you feel it, it's circulating & the thermostat is opening. When I fill a cooling system, I close it and pump the upper hose by hand. That helps fill air pockets in the system, the fluid always drops, & I re-fill & repeat the process. But I doubt that air pockets are that big a deal here because it overheats just cruising. That points to a serious circulation or airflow issue.
Here are a few pics of what is going on, just tried a 195 thermostat with no luck. Ulu I can't verify the flow due to the 90* water neck but you can feel it through the hoses and radiator. Jerry just using good old plain rubber radiator hoses can't stand those other fancy ones! elpolacko I believe the air/steam pockets may be the issue I'm battling, after installing the 195 thermostat I tried to bleed all the air out, filled the passage back full of coolant, as it warmed up it jumped in temp quite fast from about 150 to 195 then backed off as the thermostat opened. Once it was getting back up to 190 it started to puke some coolant out which makes sense as to what you are saying. That walker radiator is roughly 4 1/2" thick
I hate to suggest this, but I'd hold an exhaust gas sniffer over the open radiator with the engine running & see if you're leaking combustion gas into the coolant. Or if bubbles keep coming out but the coolant level doesn't drop, could be head gasket leaking. BTW, that bypass hose looks a bit crippled. It's sorta kinked looking.
Here are two inexpensive and relatively simple attempts to solve your problem. An air bleed in your thermostat housing. GM LT1 engines have an air bleed screw to help with purging air. The thermostat housing won't work, but you can either drill and tap yours or buy another with bosses that you can drill and tap. The bleeder itself is inexpensive. These guys are selling what looks like fish tank equipment for $17 bucks: http://www.yourcustomcar.com/coolant-bleeder-valve.html and yet another pretty neat solution and not terribly expensive either: http://jagsthatrun.com/Pages/Parts_Cooling_SightGlass.html The next suggestion is to put a higher pressure radiator cap in. 14# is normal, but try an 18 or 19# to see if it moves up the boiling point enough to stop the overheating.
If you are running a hi-flow water pump that could be the root of your problems. A few years ago I had the same things you've described happening with a new-build (SBC). It was driving me nuts (aargh!) as I had tried everything mentioned to cure it. The wife said to me one day, "Why don't you put the original water pump back on, as that's the only thing that's different now?" So I did, and it's been running perfectly (185F-190F) ever since. About 6 months later I got a PM from a guy in Atlanta, Georgia thanking me for my thread. He said he hadn't been able to drive his (BBC) anywhere without it overheating, and since changing out his hi-flow water pump it too ran perfectly. I never understood a hi-flow water pump with a restrictor. Doesn't one just negate the other?
Because your radiator outlet is lower than your thermostat housing you may have air trapped in the system. Until that air is purged, it will run hot. Also i don't see a coolant overflow tank, which you you should also have as it will catch coolant and will also pull coolant back in the system.
You may still have air trapped in the system. Remove your radiator cap and start the engine with the cap off. Let it warm up and when the thermostat opens it should let the trapped air out.
Oh I missed that entirely. Without a recovery tank, any air that is expelled is just replaced by air instead of coolant. I've had cars with bleeders, but usually never needed one on a car with a proper recovery tank. It just bleeds itself. My OT Bonnie had a bleeder, but it wasn't in the best place. The key to that car was to just fill the system with the front end jacked up, and it bled itself OK. I have seen too-high flow causing improper cooling, particularly on propane vehicles where too low a manifold temp caused the regulator to freeze up. There, just cardboard over the radiator made it run. Anyhow it's easy to test. Just put a temporary restriction in the upper hose and go run it.
Ok so went back at it again thinking what the old owner had told me how much of a pain it was to get all the air out of the system as 54 chevy recommend I left the cap off jacked it up in the front as high as I could. Bubbles came out as well as some coolant, once it settled down i put the cap back on and left it idle for 1/2 hr temp actually came down!! Ok after I shut it down it sounded like it was sucking air back into the radiator through the overflow, since I don't have a catch can could this be my problem since the filler is a tiny bit lower than the thermostat could it be creating air bubbles by itself? Would a catch can eliminate that like ELpolacko was talking about? I think I'm getting close to figuring her out! Thanks for the help guys!
Ulu! I think you just answered my question as I was typing. Off to order up an overflow can and see where that gets me. Fired it up again let it warm up and took it for a spin and it stayed right at about 200 so I think I'm getting there!
an overflow will help recover and replace any displaced coolant due to expansion or steam generation. A surge tank or Degas tank like the one on my truck or modern vehicles works because it is usually the highest point in the system. You may want to do something a bit different since you don't have the available (aesthetic) space to put a degas. http://www.jegs.com/p/JEGS-Performance-Products/JEGS-Intake-Manifold-Fill-Neck-Kits/761020/10002/-1 That would replace your existing water neck, and you would run your pressure cap there with the overflow bottle off that. Then run a fixed radiator cap on your radiator water neck or one several pounds of pressure higher than the one on the thermostat housing above.
I hope that fixes your problem. When I was a kid dad always had a Prestone bottle strapped under the hood, to catch the overflow. I've always done the same, until I finally owned a car with a factory bottle. Edith 'd' Plymouth always had a Prestone bottle, painted black, right behind the nose. It was just hung from a wire clip through the grille, which I made & sleeved with rubber tube.
This is similar to the factory setup on my '96 Bonneville, & it makes sense, especially for any car with a low hood line.
The Jalopy Journal
