Not that it makes much difference, but I don't think that's a Walker radiator. I'm also in the "check the timing" camp. After that I'd check/replace the water pump in case the impeller is bad.
I will probably get flamed by the "been done a million times with no problems" crowd, but cooling our transplanted engines needs to be looked at in its entirety. I won't address the tune-up specifics or thermostats because that's been brought up already, but let's take a look at the physics of what we do (in a basic shade-tree, common sense sort of way). First, we need to remember that an internal combustion engine is a HEAT engine. Use whatever efficiency number you want, but let's assume 65%... That means a 95 hp flat head is producing about 33 hp in heat. Now plug in a 275 hp SBC (into the same space using the same radiator), and we're producing about 96 hp in heat. We can't expect stock cooling components to handle that without helping them along: fan shrouds, air deflectors to force air through the radiator, and unrestricted air flow out under the car. A consideration to go along with with air flow out of the car is the dead air space between the top of the engine and the hood... gotta get that heat-soaked air out too (my '51 Chev pickup with a warmed up 327 holds a lot of underhood heat in this area). Louvers can help a bunch, but if you live where it rains, that limits drivability, and it also leads to the pain in the ass sanding, painting, etc. In the case of an above-the-grille deflector on a '40, a couple of up-side-down louvers may help to force cool air over the top. Fan shrouds should be setup with a way to get more air through the radiator when driving at hiway speeds: a shroud that only allows flow to the fan can act as a resistance at higher air flow created by increased ground speed... a couple of cutouts with rubber flaps located at the bottom of the shroud will allow more air to get through as you drive your "brick" down the road. Also consider the effect exhaust manifold/header temperature has on under-hood overall temp. Header wrap on headers or the first few feet of exhaust pipes will help prevent more heat from accumulating in the engine compartment. Each situation is different, but just remember, we're asking 80 year old technology and design to accommodate updates, so we have to look at the entire picture.
Does your Avatar still have the same nose down stance? If Chris' car had a similar stance then he would probably not have a heat soak issue. As air flows over and around the car the stance of a vehicle affects how this air flows and where air goes. With a lowered car there isn't as much air being pulled out from the engine bay as yours is naturally. Your stance creates a low pressure area under the car, air flows into this low pressure area, that hot engine bay air gets pulled out and allows proper cooling. A vehicle that is lowered all the way around is more likely to have stalled air flow, or worse an air cushion builds up under the nose and air pressurizes the engine bay which stalls air flow through the radiator. Air needs to be better ducted to get it moving where you want it, otherwise it just stagnates and sits in the engine bay as 28phonebooth says, Ducting may not have been commonly traditional, but air ducting tricks were used to aid a cars performance. IIRC the '57 SEDCO Black Widows had a few aero tricks to keep the FI system happy at speed.
The mechanical fan will be fine once you figure out what changed since the PO had it. My '41 p/u has a Babb radiator, an old clutch fan, no shroud or extra air deflectors and it was running @ 195 in the In-N-Out drive thru after idling for 30min in summer (and cooled right back down when air flow started again).
This set up worked, decent fan in close proximity to the radiator. Thought the deflector inside the hood controlled air bypass and the latch plate cover gizmo was just to look pretty.
Chris, no one has mentioned checking your hoses for collapsing. I have witnessed hoses sucking together on higher rpm's. Often springs were installed in them. You may recall seeing these. Might be nothing but worth a look as you investigate your cooling issue.
Since it is a new build engine you might want to check for exhaust gas in the radiator. Could be a weeping head gasket.
I just went through the same thing with the engine wanting to heat up when sitting idling. It would cool down when going down the highway. My '26 T has a very crowded engine bay. I did three things to fix it. I built a good fan shroud. I used a smaller water pump pulley to change the ratio to provide about 15% more fan and pump speed. I rerouted the belts to give more belt wrap on the water pump pulley. That high mounted alternator does not provide enough belt wrap on the WP. As you can see I have a power steering pump to deal with that is not on yours. I was able to use a longer belt to run the WP/crank/PS. You don't have the power steering, but you can go to a crank/WP dedicated belt as mentioned earlier in this thread. These three modifications worked well. My engine will sit and idle for as long as I like and it never goes above 185.
Looking at your pic of the engine, I see that you have single groove pulley on the WP. It also looks like the 7" pulley. You can get smaller WP pulleys to speed up the pump and fan. You would need 2 groove pulleys on crank and WP to go with the dedicated WP/crank belt. So you would have a little money in pulleys and belts. Less than $100 probably. Cheaper than blown head gaskets and cracked heads. WP belt wrap is more important than you would think. I bet a dollar to a doughnut that these modifications would fix your problem. They sure fixed mine.
How about rolling the alt.up and over more towards the rocker cover and welding an extension on the slotted adjuster bracket, that should put more belt surface on the pump. My avatar ruck has a cooling components fan and shroud and never overheats. Using an elect. fan will take most of the load of the water pump pulley as it no longer has to swing the fan blades. Ralphie
Chris you’ve had a lot of responses. I’m sure you will check the mechanics like timing. These are the items listed that worked for me with your set up. With the high alternator you definitely need the second belt from the WP to the crank if you keep the mount you have. There are mounts available for the left side low that may work. No over flow, keep water 1” low in radiator. Smaller pulley on the pump is great for street cruising. Remember the stock car probably had 4.11’s. Yours probably has way higher gears. 1” to radiator for the fan or a shroud. A shroud can just be a circle of metal the correct width to be over the center of the blade 1/2” off the blades for engine mount movement. Try the panel in front of the radiator. Make it out of cardboard and tape it on as a test. Same for the top but you probably won’t need that one if you correct the fan location/shroud. 5-6 blade fan. These are what worked for me when chasing heat.
There are 2 side air & a lower metal deflectors in front of the rad to keep the air in front of the rad for better air flow. Also adding the top deflector that has been recommended with all the original deflectors makes for a good duct. The arrangement keeps the air where it is needed. It would help for a more laminar flow through the rad especially if there is a fan shroud.
I agree with Fordors. The alternator is mounted so high the chrome water pump pulley does not have enough surface to bite the belt. A idler running on the back side of the belt between water pump & crank would give the water pump pulley more surface to bite instead of slipping on the chrome.
This is a great suggestion and many times overlooked, a lot of OE setups used a spring in the lower hose.
One thing no one has mentioned are the fender brace/shields at the back of the fenders. These need to be used as they help to pull the air out of the engine compartment.
The fan needs to be closer, and as mentioned block off the top inlet side to trap the air and force it through the radiator. But another issue on these older cars is the fan isn't usually centered on the radiator, so a lot of radiator core doesn't get air pulled through it, which results in running hotter. A fan shroud will help a lot to direct air to flow through the whole core. And in a pinch you could run an electric pusher fan on the front side with a thermostat to call it on. Set it higher up to compensate for the mechanical fan sitting low. I use this setup on my '39 Chev and have the stat set at 185 degrees. It keeps mine from ever going over 195, even on hottest days.
My '40 coupe with a 375 HP Rochester injected 327 runs at 180F all day in traffic, 96F air temps. I use a Walker 17 inch fan and shroud on a Walker radiator. 40 years operating with this set up.....recommended to me by Vernon Walker.
I had some weird cooling phenomena on my 40 with sbc and the greatest help came from installing a Robert Shaw high flow thermostat. It was the 5th and the last one I tried. It was even better than drilling holes ( 2-3/32 in holes in Napa stat). Sent from my iPhone using H.A.M.B.
I would be willing to bet that after you install a fan shroud and close off the top of the grill your problem will be solved.
Louver the hood to let more hot air out, no big science involved. Also 40's had a rear fender brace that was a shroud, sometimes people leave them off, they're needed to direct air flow.
Thanks again everyone, there are some really good ideas I did not even think of being brought up. This will be a winter time project, nothing I am messing with at this very moment. So I apologize if I draft a thread and then go silent for a bit. I will start trying some of these things and will report back eventually. Thanks all, and MERRY CHRISTMAS!
Here's something else to consider, and I almost forgot it until this morning. I had a real cooling issue with the BBC in my '63 Falcon gasser, even with a huge aluminum radiator, and electric puller fan! It ran hot all the time, and anytime I stopped in traffic I was immediately watching the gauge to see if I needed to get out of traffic. I tried adding an auxiliary small radiator even in an attempt to add more cooling, but it did very little to help. I was complaining to a buddy about the issues, and we discussed how far it had been bored, plus other cam specs, etc. Nothing brought up concerns until he asked me about carb jetting on the BBC. I told him I'd never checked because the engine ran so well. But I went home and pulled the bowls on the Holley carbs to check. I called him to tell him the jet sizes and he recommended an increase in jet size of about 10-12 sizes larger. Not having spare jets I simply got my numbered drill set out and drilled all the jets out. I took the car out for a drive and it ran 20 degrees cooler, and never got over 190 even idling in traffic. I went home and pulled the auxiliary radiator off also, and it still ran cool. Lesson learned that a too lean carb can really cause overheating and still run really well.
Ok...well I have not actually messed with it. I have NOT checked the timing or done anything. That will be first on the list. However, I was out in my garage so decided to at least open the hood and take a peek. Water pump pulley is 7”. I am not sure if that’s normal or what. Fan is 2” from radiator. Yes, the little shields on the grill sides are in place, as well as the pan below radiator. I see what you guys mean about the height and angle of the alternator. I can grab the fan and easily turn it without turning the belt. The belt also does not seat into the grove that well. I’m assuming it’s an aftermarket pulley. Im still going to check timing first. If that seems ok, I have a friend donating a GM power gen to the cause so I will address the alternator/belt issue then. I can raise the radiator if necessary and get a stock style fan closer and possibly add a shroud. Sorry, these pics are dark, hopefully you get the idea
Another idea is, the long water pumps flow more, and you have plenty of room for it. Since you are going to remount your alternator anyway...
You mentioned the rear fender braces, are these the ones behind the front wheels in the fenderwell? Big 348 with fenderwell headers in my 40, I think cooling may be an issue, despite louvered hood..
I’m pretty sure that a big part of your cooling issue is that fan. Those flat on the front flex fans just don’t move enough air. I tried one on my RPU and it was useless. Overheating. So I switched it out to a Derale steel fixed blade race fan and the problem was solved believe me the blades of the Derale fan really move air. That and a spacer to put the fan an inch away from the rad and you should be good. https://derale.com/product-footer/b...shroud-kit2013-10-18-11-52-51999354306-detail
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