BulldogDriver Posted April 18, 2023 Share Posted April 18, 2023 I’m trying to chase a problem with my engine running hot all the time. The temps around here in North Carolina have been in the 70-80’s lately. The engine is climbing up to 203-208* range whether it is below 50mph or above. It hasn’t overheated and I have put about 1000 miles on it since all of the upgrades and rebuild. Problem doesn’t seem to change with A/C on or off. Everything is either new or verified as new. Engine ran fine on 3000 miles cross country 4 years ago with speed up to 80mph. Engine did not over heat or show signs of running hot. I didn’t have a temperature gauge on it at the time so don’t know what the true temperature was and didn’t use the A/C as it had problems. Cylinder walls were glazed and was the only reason for pulling engine a part. Fresh rebuild on a 401 0.60” over with moly rings and Best head gaskets. Timing is set at 12* with 30* max on a rebuilt distributor with an electronic conversion kit. Vacuum is on the ported side of the carburetor. Timing verified as correct though out the rpm range. Cooling system has been gone over with original 3 row radiator cleaned and verified not clogged by a reputable shop. 160* thermostat, FlowKooler water pump, original 5 blade fan, 16# cap, new HD Hayden fan clutch #2747, fan shroud with baffles around the perimeter to make sure all air is pulled through the radiator, and original A/C pulleys. I have changed out the original A/C to a Vintage Air completely. The condenser is the largest I could fit and covers the front of the radiator almost completely which, if I remember correctly, was the way the original one did. I have also changed over to a 4L60E transmission that uses the radiator cooler along with an external cooler that sits in front of the radiator and condenser at the bottom of both. I know that the shown temperature is correct as it shows the same on the temp gauge and on the transmission controller, within a few degrees. Here’s what I don’t know: How far from the radiator did the condenser originally mount? What are the dimensions of the original condenser? How much hotter would a .060” bored engine run? How much more taxing is an external transmission cooler to the cooling system? My thoughts of the next thing to do is: Eliminate the external transmission cooler. Remove the baffles I added to the shroud. Move condenser further away from the radiator. Thoughts? Ray Link to comment Share on other sites More sharing options...
RivNut Posted April 18, 2023 Share Posted April 18, 2023 203 to 208 degrees is not hot. If you’re not having boiling over problems, there’s really no problem. If you didn’t have a temp gauge, would you even know it was “hot?” 2 Link to comment Share on other sites More sharing options...
tenugent Posted April 18, 2023 Share Posted April 18, 2023 Ray as Ed said that isn't hot.My 63 got to 230 on the way back from branson last year so I babied it home and had my radiator recored and new fan clutch.I have my radiator shroud sealed to radiator also.I haven't had a long trip yet so I can't see if upgrades have helped alot.On short drives it's about 195 to 200 so I'm pleased with that.Ive also read that when boring these nailheads they will run hotter,mine a 30 over 425.Ill get it on the highway for a couple hours and report back.T.N. 12969. Link to comment Share on other sites More sharing options...
Matt56 Posted April 18, 2023 Share Posted April 18, 2023 I agree 203 - 208 is not hot but understand may be higher than you would be comfortable with. Is their any particular reason you have connected distributor vaccuum to ported? Not that it would help with cooling at driving speeds but at idling you may get some cooling benefit by connecting to manifold vacuum. Link to comment Share on other sites More sharing options...
Matt56 Posted April 18, 2023 Share Posted April 18, 2023 Also, noting the additional transmission cooler - how large is that? I've never experienced the addition of a cooler causing issues but is it likely to be impeding airflow? Link to comment Share on other sites More sharing options...
RivNut Posted April 18, 2023 Share Posted April 18, 2023 7 minutes ago, Matt56 said: Also, noting the additional transmission cooler - how large is that? I've never experienced the addition of a cooler causing issues but is it likely to be impeding airflow? Exactly, anything in front of the radiator will affect cooling. Even if the fins in the a/c condenser are not lined up correctly, or if any of the fins are bent over not allowing air to flow through the radiator. As Tim said, make sure that you have the radiator sealed to the radiator core support. Run the factory a/c fan with a shroud. Make sure the fan is positioned correctly within the shroud. Lots of little things to consider. Plus a bored engine typically runs hotter than a stock bore. Link to comment Share on other sites More sharing options...
BulldogDriver Posted April 19, 2023 Author Share Posted April 19, 2023 (edited) Attached are a few photos of the baffle I added. Baffles are used in aviation to make sure air is controlled to be able to get the best heat exchange possible. In this case to completely go through the radiator then out the back of the engine compartment. The same amount of air is moved by the fan with or without the baffle. Though it may not be much of an improvement I wanted to get as much air through the radiator as possible with the engine running as hot as it does. The shroud is attached and positioned the same way as it would be if the baffle was not used. I have read that the fan blades should be partially outside of the shroud but if you look at the one photo, the blades are only about a 1/4 to 3/8” outside of the baffle. I was under the impression that they needed to further out. The shroud is a repop. The external transmission cooler is at the bottom of radiator and runs across the entire width. An external cooler was recommended by the rebuilder. Please ignore the position of the air cleaner snorkel, there are 2 other openings of the same size in the rear of it. It has to be in this position due to a TPS (Throttle Position Sensor) mounted on the carburetor. A lot of work on the air cleaner to make this fit on the Edelbrock carb. Ray Edited April 19, 2023 by BulldogDriver (see edit history) Link to comment Share on other sites More sharing options...
avgwarhawk Posted April 19, 2023 Share Posted April 19, 2023 (edited) Remove the temp gauge. It's not running hot at the temp the gauge is indicating. Edited April 19, 2023 by avgwarhawk (see edit history) Link to comment Share on other sites More sharing options...
tenugent Posted April 19, 2023 Share Posted April 19, 2023 Ray I measured my fan outside of shroud and it's the same as yours.Go to post war buick forum and machinegun has a post about fan placement in shroud. Link to comment Share on other sites More sharing options...
MrFreeze Posted April 19, 2023 Share Posted April 19, 2023 Why would a rebored engine run hotter than a stock bore? Is the engine making more heat now? Maybe, if you also modified it with some performance parts during the rebuild (hotter cam, modified heads, etc). If not, it is making the same heat it always did, and that heat is leaving via the radiator, the same way it always did. Thinner cylinder walls will have no effect on this process. Thicker walls do not "store" heat" and magically transport it away. This old wives tale has been around for decades and still seems to have traction. Kind of like the one about coolant going through the radiator "too fast" if you don't have a T-stat installed. Not trying to ruffle any feathers, but I have spent a lot of years in the heat transfer profession, and I can tell you unequivocally that, by itself, reboring an engine does not make it run hotter. This information comes to you not from a car guy (which I sort of am, kinda), but from a heat transfer engineer with 2 degrees and 30 years of experience (which I definitely am). Getting back to your problem, as stated by others, up to 208F is not really a problem, and if your temp is consistent during idling, cruising, and high speed driving, then 208 might just be what your thermostat is controlling at. But if your temps change depending on driving type or ambient conditions, then you have an issue with your cooling system. With a 160F T-stat (why so low?) I would expect your consistent temps to be lower than 208. The addition of a trans cooler is definitely impacting the situation - you have impeded airflow through the radiator, and also pre-warmed it even more than just the AC condenser would do by itself. Where are you temp gage senders installed? In the factory location, or somewhere else? A couple of random thoughts - you mentioned an Edelbrock carb, overdrive transmission, electronic ignition - any other performance mods? As I mentioned, more power made definitely equals more heat needing to be shed via the radiator. Also, moving the condenser away from the radiator probably won't do anything much, except maybe make your AC not work as well and take more engine power to run. Was the engine hot-tanked before the rebore? I'd "assume" it was, but that can be dangerous thinking... Good luck with this issue - hopefully this excellent forum can help you sort it out. MrFreeze Link to comment Share on other sites More sharing options...
RivNut Posted April 19, 2023 Share Posted April 19, 2023 What I’ve been told is that the thinner walls of the cylinders don’t hold the coolness of the water in them and more heat is transferred to the circulating water. I have no idea if what I was told makes any sense technically, but I do know that ever since I bought my 66 back in 1973 and started messing with nailheads, everyone that I know who has bored out a 401 or a 425 has seen some kind of an increase in the operating temperature of those engines after the rebore. 1 Link to comment Share on other sites More sharing options...
EmTee Posted April 19, 2023 Share Posted April 19, 2023 9 hours ago, MrFreeze said: A couple of random thoughts - you mentioned an Edelbrock carb, overdrive transmission, How do the sparkplugs look? With a different carburetor and an OD transmission the engine might be operating a little too lean. Link to comment Share on other sites More sharing options...
Jim Cannon Posted April 19, 2023 Share Posted April 19, 2023 Is the little butterfly valve mounted on the passenger side exhaust manifold free to move and opening when hot? For this transmission (not a Dynaflow) I think you are better off doing the ignition timing like they call for on the 1964-66 nailhead with an automatic transmission: don't use ported vacuum and start with initial timing (no vacuum advance connected) 2.5 degrees BTDC. Did you check the temperature gauge calibration before you installed it? Is it a mechanical or an electrical gauge? How many rows of tubes does your radiator care have in it? 2? 3? 4? Link to comment Share on other sites More sharing options...
Seafoam65 Posted April 19, 2023 Share Posted April 19, 2023 203 to 208 is NOT HOT!!!!!!!!!!!!!! If your car had an idiot light it would come on at 240. Drive your car and quit staring at the temp guage....it is fine. 1 1 Link to comment Share on other sites More sharing options...
RivNut Posted April 20, 2023 Share Posted April 20, 2023 Remember. A 195 degree thermostat opens at 195 degrees when the engine comes up to an operating temperature of 195 degrees. It DOES NOT keep the engine at 195 degrees. The radiator does that. If the radiator can cool your engine to something cooler, the thermostat will close and reopen when the coolant temperature gets up to 195 degrees. The thermostat keeps the engine hot enough to run an efficient operating range. 1 1 Link to comment Share on other sites More sharing options...
Seafoam65 Posted April 20, 2023 Share Posted April 20, 2023 On my 1995 Corvette, GM designed the electric cooling fans to come on at 227 degrees if the A/C is turned off. The fans run with the A/C on because the condenser for the A/C has to have constant air flow. 1 Link to comment Share on other sites More sharing options...
Wayne R Posted April 20, 2023 Share Posted April 20, 2023 Have a read of this,----go to google, put this in. Should you run a 160 degree thermostat,---Bad luck garage. Link to comment Share on other sites More sharing options...
BulldogDriver Posted April 20, 2023 Author Share Posted April 20, 2023 Everyone thanks for the replies. I’m out of town till Tuesday and will respond when I get back. Ray Link to comment Share on other sites More sharing options...
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