Our 261, with a 235 head, which is mounted aft in our 1945 Flxible Clipper, takes very little time to warm up and runs warmer than we anticipated it would.
We have flushed the engine, having found much 'muck' behind number 6, thoroughly. Removed the water pump up front, as well as all core plugs, blasting and running water until no more muck or discoloration of the water was observed.
We have a new radiator, with two (2) 16" electric fans sucking through said radiator, switched - but nearly always on. While driving, road air is jammed down from a scoop on the roof, across the radiator, in the same direction as the fans suck air.
It warms to @180 in short order and seems to run @200 when going down the road. It climbs above that, though does not/has not boil(ed) over when at idle.
There is no thermostat in the system, as the shutterstat system opens/closes the shutters based on coolant temperature. As such, coolant is always flowing wide-open through the engine and radiator.
We have 2" lines running to/from the radiator/engine.
What is the optimal operating temperature for the 261? Is 200 too warm?
What pressure rating does the radiator cap have? Every pound of pressure on the cooling system raises the boiling point 3 degrees at sea level. A 15 pound cap keeps the coolant from boiling all the way to 257 degrees, and as long as the coolant is liquid, it's still moving heat from the engine to the radiator. If the engine doesn't go above 200 on a hard uphill pull, it sounds like you're OK. If you want to run a lower coolant temperature consistently, you're going to need a bigger radiator or move more air volume over the one you've got. You could also install a restrictor washer in the thermostat housing to slow down the coolant flow- - - -it might not be spending enough time in the radiator to get cooled adequately before going back to the engine to pick up more heat. Use a laser temp gun to evaluate the efficiency of the radiator- - - -aim the gun at the inlet and outlet nipples of the radiator to see how much heat is actually getting transferred to the cooling air. The results might surprise you. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
I will have to check the cap. It is a bugger to access and take off.
We are getting +/-20F drop across the radiator, with the electric fans on, sitting at idle. It varies, but it always pretty close to 20F drop. If the numbers matter, 178F up top and 158F on the bottom. That is read on the tanks, as the nipples are covered by the radiator hose(s).
The hottest point in the whole system seems to be the thermostat housing. It is a pretty solid 220-230F there. Moving over inches (as in 3-4") to the radiator line, it drops 40-50F, which seems odd, but I checked it a number of times to confirm.
The radiator is coolest, right between the fans, dead center in both directions. It reads 120F there, rather steady.
Attached is an older photograph of the setup we are running. Fabricated here on the farm, not the least bit stock. The stock radiator, while thicker from front to back, by about 1.5 times, is nearly the same size in all other dimensions. That radiator is beyond repair, or so we have been told, but we have it in case we run into someone that wants to rework it on the cheap. The stock setup did NOT have electric fans and relied entirely on air from the roof scoop, which is why we are puzzled with it running hot, WITH the fans.
I think I'd try restricting the flow rate a little, to give the coolant more time in the radiator. Don't overdo it- - - -mabe reduce the diameter of the hole in the thermostat housing by 3/8" or so, maybe 1/2" at most. Online racers' supply places like JEGS of Summit will have the reducer washers in whatever size fits the housing. I've made a little more durable ones from a piece of 1/8" thick aluminum with the edge thinned down to fit the counterbore in the housing. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Heat produces power so the more heat you can generate the more power you can get. My wife had a Buick station wagon that the first fan didn't come on till 238* and the second came on at 256*. Of course a lot of this was to meet emission standards. If your cooling system components can take the pressure run a <> 10# cap and throw the worries out the window. The qualifier here is you have oil that won't break down or clearances that won't seize.
If you reduce the flow through a heat exchanger the heat transfer rate will be reduced (q=UAdT). Less heat transferred in the radiator means the engine temperature should rise.
First troubleshooting process question, what changed? The radiator? The radiator is smaller ("stock radiator, while thicker from front to back, by about 1.5 times") and the picture appears to show fans that move air across 60-70% of the radiator.
First troubleshooting process question, what changed? The radiator? The radiator is smaller ("stock radiator, while thicker from front to back, by about 1.5 times") and the picture appears to show fans that move air across 60-70% of the radiator.
Harold,
Correct, the radiator changed. That said, we never ran it with the factory radiator as it was unable to hold coolant long enough to try it. I would say your estimate of fan to radiator is correct, however the factory setup did NOT have any fans other than the standard engine fan - which we still have, but it does nothing to push/pull air across the radiator as it is 3' below and 3' behind the radiator.
It's tough to get a feel for how this is setup from the photograph. The radiator is about 5' off the ground, sitting at about a 15 degree angle, such that air gets jammed across it from the roof air scoop. The engine sits backwards, when compared to a 'normal' engine orientation. The engine has the stock fan, but as noted it above, it does little else besides blowing air and presenting an in-your-face body part remover if you are not mindful of said body parts.
Restricting the flow rate through our racing radiators always resulted in the engine running cooler. Of course, at extreme RPM, it's possible the water pump impeller was cavitating and reducing its ability to move the coolant. I'm still thinking the most likely culprit is reduced radiator capacity. An aluminum radiator sinply can't transfer heat as efficiently as a copper core OEM style. If you have enough room, which it seems like you do, put a bigger radiator in there and solve the problem. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
I have used a surfactant called "Water Wetter" on my rig. It is supposed to improve heat transfer from the metal to the coolant and vise versa. It helped some, maybe 10deg.
Also, I have run across situations where the crank pulley was slipping on the rubber it was supposed to be bonded to. So the water pump/fan did not turn as fast as expected. This problem took me much too long to figure out.
I have run Chevrolet 235s for many years and 200+ water doesn't seem to bother them. Running continuously above 2800RPM does heat the oil to 250 and up. I don't think that's good. Do you have an oil temperature gauge? On a 261 with an external oil filter you could install an oil cooler if you find high oil temperature.
1951 3800 1-ton "Earning its keep from the get-go" In the DITY Gallery 1962 261 (w/cam, Fenton headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971.
I’m currently running a 261 in Texas (100 degree days already). I have an aluminum radiator, 7 lbs radiator cap, pusher fan, 160 degree thermostat, and 848 heads (with steam holes). Have not had an issue getting above 190 degrees yet.
Do you have the correct steam holes in your head or have a gasket blocking a hole?
Just a thought. You’ve gotten pretty good advice in this thread!
Do you have the correct steam holes in your head or have a gasket blocking a hole?
Chris
Chris,
Thank you for your post. I have only just recently become aware of the steam holes 'issue'. I have not the first idea if the holes are present and/or a gasket may be blocking said holes.
If other remedies do not resolve the high operating temperature (high by my estimation) we may have to pull the head and have a look. That is not something I have ever done but suspect we could figure it out.
"Steam hole" is a misnomer. The holes in the head are there to provide coolant flow alongside the three pairs of cylinders that are "siamesed" together without a gap between them to allow for the big pistons. An 848 casting number head can be drilled to work with the 261 engine by using the 261 head gasket as a drilling template. The small block 400 V8 used the same system to avoid hot spots when the cylinders were siamese-cast to allow for a 4 1/8" bore size on that engine. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
I used waterwetter in my race bikes which were only rode when warm out and kept inside. Although it’s good for heat (racing), I’m not sure if I’d use it in the great white north. It changes the freezing temp of your radiator fluid mixture which will cause issues next fall when the tundra freezes.
The only reason we ran water wetter in the race engines at Nashville was a $500.00 fine by the track management for getting caught with antifreeze in the engines. Even a tiny coolant leak while running antifreeze left the track as slippery as snot! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
