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Car was running hot before I replaced the pump with the new GMB unit. The GMB does have a stamped impeller. Is there a way to test if the impeller slips or is it just replace and try?
I had to replace and try as I would have had to remove the pump anyway to grip the input shaft and try to turn the impeller against it. Once you have the pump off, you can try that to see if it slips...
Yeah, I'd confirm your speedo by using a portable GPS or downloading an app for your smartphone and checking it. Using a quickie online calculator, w/ a 4.10 rear gear and 26" tall tire, you should be going 75.5 MPH at 4000 RPM in 3rd gear (although I doubt this calculator accounts for TC slip). Better yet, jack up the rear, spin the driveshaft and count the wheel rotations to determine your rear end ratio directly. My suspicion is that a prior owner increased the rear end ratio and pushed the cooling demand above what the factory radiator can provide. At speed, you can't blame the smaller than stock fan for this.
Last edited by JohnnyBs68S; April 9th, 2020 at 10:17 AM.
Yeah, I'd confirm your speedo by using a portable GPS or downloading an app for your smartphone and checking it. Using a quickie online calculator, w/ a 4.10 rear gear and 26" tall tire, you should be going 75.5 MPH at 4000 RPM in 3rd gear (although I doubt this calculator accounts for TC slip). Better yet, jack up the rear, spin the driveshaft and count the wheel rotations to determine your rear end ratio directly. My suspicion is that a prior owner increased the rear end ratio and pushed the cooling demand above what the factory radiator can provide. At speed, you can't blame the smaller than stock fan for this.
Thanks Johnny. Tried two GPS apps and they show speedo is off by 5mph. So instead of 60, it shows me going 55.
Thanks Johnny. Tried two GPS apps and they show speedo is off by 5mph. So instead of 60, it shows me going 55.
Well at least it's wrong in the right way and will help prevent you from getting a speeding ticket. One of my cars is slow by 5 MPH, and the other is fast by 5 MPH. The problem is I can never remember which one is which.
Last edited by Fun71; April 9th, 2020 at 05:10 PM.
Thanks Johnny. Tried two GPS apps and they show speedo is off by 5mph. So instead of 60, it shows me going 55.
Ok, so instead of 4000 RPM at 70, you are going ~65, an even larger difference than calculated. Unless you are running a really short tire (it doesn't appear so), the suspicion of a higher gear ratio is even more pronounced.
I read of a fix for a problem like yours was to change the pulley diameter. Spinning too fast or too slow can have negative effects on engine temp. I'm not saying this is the problem but if the pulleys were replaced as some point it could change engine cooling.
I read of a fix for a problem like yours was to change the pulley diameter. Spinning too fast or too slow can have negative effects on engine temp. I'm not saying this is the problem but if the pulleys were replaced as some point it could change engine cooling.
This fact is very evident when comparing the non A/C vs. A/C pulleys on these Cutlasses. The non A/C water pump pulley is very large when compared to the A/C pulley, while the crank pulleys differ by a small amount. According to specs I read, the non A/C fixed fan turns .85 of the crank, so slower, while the A/C clutch fan set up turns 1.4 times of the crank, thus providing superior cooling at idle speeds based on my understanding.
Coolant cavitation could be the problem. It would makes sense about a problem in the 3,400 to 4,000 RPM's and highway speeds for a period of time. Cooling problems could appear at lower speeds if the pulleys were changed. There may be a reason why Oldsmobile didn't offer A/C with certain rear end ratios.
Water pump pulley was marked KK so it appears correct for a 71 455 A/C Car with PS. I wasn't able to see the code marked on the crank pulley.
With the calculator Johnny recommended, it appears car has 4.10 rear. I would have anticipated a lot more off the line or smoked tires with that kind of rear. It does kick in hard though shortly after off the line. Again, perhaps back to timing.
I've been told GM had concerns with the belt coming off the A/C pulley at higher RPMs back in the day but that usually just resulted in a lower redline.
I do appreciate everyone's input and help. Ordering some parts and hope to try some of the recommendations next week.
These are pictures of two factory closed impeller water pumps that I have in the garage. I don't know if the differences are the same for all years or not, though.
Non-AC water pump with large impeller on the left, AC water pump with small impeller on the right:
Interesting topic, as I just installed a 5.5" non A/C pump on my 71 SX with a clutch fan and the set back water pump pulley and compared the impeller size in that pump to a 6" water pump designed for an A/C car and there is a huge difference. I was wondering the theory/reason for the differences. I presume it's tied into the speed the water moves through the rad for the given RPMs of the engine.
I was wondering the theory/reason for the differences. I presume it's tied into the speed the water moves through the rad for the given RPMs of the engine.
That was the consensus in the discussion many years ago, that the engineers matched the impeller and pulley to achieve the correct coolant flow rate and not have cavitation, and also to have the correct fan speed.
Interesting. I didn't measure the impeller size before it was installed. I went with the GMB 130-1260P as it seemed others with 455's and A/C had good luck with it. Tech at Summit Racing said it was specifically for cars with A/C or HD cooling.
I didn't read through entire post. Have you checked inlet and outlet temps of radiator? Should be a 10 degree difference.
I replaced the fan,clutch, and removed the t-stat today. There is a 10 to 11 degree difference between the inlet and outlet of the radiator when running at idle. Does this mean radiator is ok?
Still seeing issues with overheating at higher speeds all though it seemed to increase a little slower. Idle seemed to top out around 200 degrees without A/C on and after a while got to 215 with the A/C on before I shut it off.
The HD clutch is shorter than the standard one and the fan seemed to stick out about 1/2 to 3/4 inch from the shroud so I tried this run with the standard clutch.
Still waiting on the spring to try in the lower hose.
Years ago a friend started having issues with the engine running hot at highway speeds, but all seemed well at lower speed. After lots of troubleshooting, he eventually pulled the radiator and found that a field mouse had built a nest between the radiator and the AC condenser, and the nest was partially blocking air flow. After cleaning out the nest materials (and a cooked field mouse) the engine temps went back to normal at highway speeds.
Hi FL442 - were you able to resolve this? I am having the exact same issue. I was thinking of ordering a
FlowKooler 1775P - FlowKooler Hi-Flow Mechanical Water Pumps from Summit...
Still working on it. Waiting for a few more parts and a timing adjustment. If I had found the non-polished version of that before, I probably would have gone with it. Apparently it used the GMB aluminum housing but a specially designed impeller.
It was a hot 90 deg FL day and I ran the car with a new taller HD clutch (hayden 2747). I was able to do highway speeds with the car topping out around 210 deg. You could hear a fan roar kick in and it would drop to about 200 or 205 before the roar stopped and it would go back to 210 and the process repeat. Ran with A/C on and off. Same result. This is much improved over the uncontrollable heating at highway speeds. This has me somewhat concerned though as it should be kicking in at a lower temp and staying engaged longer. Hayden says 180-190 engine temp and a 20 deg drop before disengaging. Defective clutch? Other area to check?
Car does heat at stop signs or traffic lights up to about 220. Idle is only around 700 RPM at that point. Still waiting on update timing and it looks like the post office lost the lower hose spring in the mail. :\
Are all the shrouds and baffles present around the radiator? There are tar paper-like shrouds the clip to the radiator top plate and then to the core support. One on each side. There are also rubber insulators that clip to the core support to take up the space between the radiator tanks and the core support. There are also shrouds around the bumper brackets, all designed to funnel air thru the radiator.
Matt, I just realized I don't have the side rubber sheet seals. Do you know which version is needed? I see two types. One is short and fat, the other longer and narrower.
In another thread, a temperature difference between head was measured. The problem turned out to be caused by a frozen stuck heat riser. Did they even still use them that late?
The Flowkooler or a factory closed impeller pump rebuilt is the way to go. No doubt those flaps make a difference, get them in place. A big two core aluminum like the Cold Case rad, Flowkooler pump and factory flaps is the way to go. It sounds like insufficient air or coolant flow at low speeds and too small a rad at high speeds. I know you guys get very hot down there but at highway speeds the fan should be doing minimal. I added the GN surround flaps and the larger A body rad to my 88, no fans needed in this cool weather with this 8 to 1 350. I had endless cooling issues with it when it had a 403, tiny Euro grills don't help. I would hit 230+ towing, 195 to 215 with a Champion 3 core, not a big enough rad. As said, check with a IR gun. Mine gauge was showing 40 degrees difference, must have been an air pocket.
Mechanic and I have gone through a number of steps and tried various recommendations from folks in this thread. Thank you all for your input.
We have reached at point where I at least feel comfortable with the temp. The new fan and clutch made a big difference. I was able to source a 19.5 inch fan from a later 70s chevy 454. Keeps the temp below 210 at very high RPMs and speeds. You can hear the clutch lock up at high RPMs once the temp gets over 200, close to 210 and the temp starts falling.
It appears part of what has been driving the temp issue was crud in the block. The regular flushes didn't get this out. I ended using the Evaporust Thermocure and it got a lot out. I plan to do another run with that soon.
An unexplained situation we have though is the rear ratio and speed vs RPM. As you can see form a few early posts, it looked like the car must have a 4.10 or similar rear based on speed/rpm/tire size. However, count the driveshaft spins for one tire rotation, we get something like a 3.08 rear. I will probably have to start another post for that one. Makes no sense.
No need to start new thread. Just pop the diff.cover and have 110% accurate answer instead of 20+ something posts quessing whats there, until you still pop the cover....
It seems, he indeed did answer his own question. It's as simple as revolving the tire until the valve's at high noon and then marking the driveshaft with a piece of chalk. Then, count the driveshaft revolutions for every wheel revolve. He'll either get 2:78, 3:08 or 4:11, being that there are no in betweens
I got 3.08 as I mentioned. That is the rear ratio. There is no point to count gears. I am trying to figure out why based on RPM, Tire Size, and Speed calculations it shows something like a 4.11 ratio. As others suggested I am going to try a second tach. Maybe with the conversion to petronix the voltage is off to the stock tach.
If you're running a stock tire size, then you've evidently got the wrong speedometer gear installed in your transmission. Wasn't this previously mentioned, on this thread?
I second the support of flowkooler water pumps. They have great impellers & are quality parts. I use them on both of my big blocks. Looks like I last messed with this stuff in 2016, so that's a point for parts durability too. The data below is from 2 66 big cars, so it may be a little different for your A body. One of my cars is a '66 425 with no A/C, the other is a '70 455 with A/C. Both have 4 core brass radiators.
I hate over heating old cars so much they both have 160 degree robertshaw thermostats and 74 Eldorado puke tanks. I'm getting to believe 160 might be too cool, but can't quite bring myself to return to the stresses I felt long ago when I ran a 180. The cars get up above 180 anyway on longer drives, so not a big deal, just a question in my head.
Be sure the fan shroud rear of the radiator is in good shape. If you want, add a rubber seal to the leading edge of of the shroud to really seal it tight agains the radiator. Not stock, but it might help. See the Trimlok catalog for seal shapes, measure the width of the lip and get a seal with a U channel that more or less clamps on the front of the shroud. My guess is your radiator is 1/4" thick plastic for reference. Just a guess.
Next there should rubber pieces in front of the radiator. My '66's have 3 - left, right, and lower. You can get mastic rubber from Fusick by the roll & remake yours. The idea is to have those seals tight enough to force air into the radiator and not around it on the top, bottom or sides. I've just redone my Starfire and the bottom one was original factory and full of holes and tears -- meaning air leaks. If you want to get creative, cut the side seals extra long so that you can tuck the top "ears" in under radiator top plate and really force air through the radiator. With those seals tucked under the top plate, it creates a really clean look when you pop the hood too.
I think you have the word on the fan itself, my advice would be to go stock which I think is 19", maybe 19.5. I prefer the 7 bladed fans over the 6 blades, but that's just instinct, not testing. More blades = more airflow? Don't know, but I'm running 7 bladed fans now.
There's magic in the clutch fans though. Hayden has a whole catalog of clutch fans that fit our 455's. My old test resuts refer to the 2705 standard duty, 2747 heavy duty and 2765 standard duty parts. What I learned on my mid 60's big olds (can't remember - probably the Starfire with A/C) is that the 2765 runs quieter but hotter, the 2747 is noisy and cool. I'm running the 2765 now and have since 12/2016. It looks like the 2772 and 2797 may also fit mid-60's big olds. What Hayden varied in standard vs. heavy duty was the cut in temperature, length of the clutch fan fore/aft, and depth of the clutch fins. HD clutches cut in at a lower temperature, SD clutches run quieter and cut in at a higher temperature. Then the question is how long the clutch should be. The rule of thumb I recall is to have your fan blades halfway in the shroud, with the rear half of the blade out. Mine aren't quite that, but close.
FWIW I briefly tested some Dorman plastic modern fans to see if 11 or 12 smaller blades would pull more air. They didn't help. Factory style was the way to go for me.
April 9th, 2020, 09:25 AM
