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Mysterious slow heat creep in a 65 w/5.0

1343 Views 16 Replies 8 Participants Last post by  The Greek
I've asked for suggestions before on this same issue, and they sorta worked, but I'm back because I'm still concerned.
Back story:
Dropped in a 5.0 from a '91 F150
Kept 289 front end dress (v-belt pulleys, 50oz 289 balancer etc)
Had humongous overheating issues
replaced thermostat
replaced water pump (edelbrock victor high-flow)
replace temp sender for mechanical gauge
added fan shroud
changed from flex fan to rigid 5-blade
removed fan shroud
replaced thermostat
replaced radiator with new 3-row copper
replaced thermostat
replaced radiator with new 2-row aluminum
replaced WP pulley with correct size (old one was incorrect for car and slightly underdriven)
and used roughly $150 worth of coolant and Redline water wetter at regular intervals in that list.
The symptoms:
At first startup, engine heats up, albeit very rather quickly, approaches 'stat temp (180), fluctuates, holds around 190ish. Fine.
After running for more than an hour, temps start to creep up. This is in 60-70 degree weather. Usually she'll peter out around 210-215, but the engine does not like it at all, starts stumbling and idling extremely rough. Pick up the rpms and it drops to about 200, but the process restarts at the next red light. The other day it was 80 here and the temp gauge hit 235-240. Very, very concerning.
One thing I did notice while watching the top of the radiator to ensure 'stat was opening was that flow seems awfully sluggish. i remember a time with the 289 i looked in there as the stat opened and hot coolant came gushing across the top of the radiator. Now i cant get it to do that even by picking up the rpms.

At first I attributed the heat to the recent overhaul and over-bore the engine got, but this is nearly 2500 miles after that happened. The one, final thing that comes to mind is this: while the engine was on the stand, I had rags galore in all the holes so no dirt/debris would ruin the fresh motor. I would swear that i got each and every rag out of the block, but.... a blue shop rag in a cooling passage would certainly cause the sort of ailments I'm seeing...

Thoughts? Criticisms? Want to call me a moron? I'm 99% out of ideas. Would a high-pressure reverse flush be enough to force a rag outta the block? Or should i bite the bullet and disassemble the entire engine one final time and search every nook and cranny ?
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Does it have underdrive pulleys? If so swap back to stock. I would also put the shroud back in, that does a lot of good to cool it down. Maybe check and make sure the stat is in right (though if it were backward you would have obvious signs)...

A rag in the coolant passages would certainly be a problem, but you'd have to be in heck of a hurry slapping it together to overlook a rag in there.
No underdrive, stock pulley size of 5 3/4''. Problem with shroud now is the one i had bought was for the stock radiator, and I forced a larger aluminum radiator A-la Mustang Steve style...
Stat is in the right way around, triple checked the last time I put a new one in.
I may have been in a hurry to finish the project at the end when my parents wanted their garage back, but when I was assembling the long block on the stand I (thought) was taking my time....
somebody back me up or say I'm wrong...does that motor use a "reverse rotation water pump"? If so, that could be your problem
this may seem a no brainer but did you install the head gasket correctly? it only works one way and if you did it backwards it would overheat. -doesn't seem this extreme though.

how far overbore did you go? I would think that much over .40 is pretty large.

did you forget the backing plate to the water pump? that would cause the problems you are experiencing also.
if its an 80s engine and timing cover then it uses the reverse flow pumps I believe. at least that's how my 86 is.
- I think the symptoms you describe best point to issues with your water pump.

it really never turns out well when a build is being rushed
I think 2ManyMustangs is on the right track. The 5.0 have reverse flow, and you kept the 289 front dress. They changed to reverse flow to enable the use of the serpentine belt setup.

So the question is if your new Edelbrock pump is standard or reverse flow?

A shroud is essential in my opinion. There is a reason all modern cars have those. :shiny:
A stock 91 5.0 does use a reverse-rotation water pump, but I retained the 65 style timing cover so the dipstick and timing pointer would be in the right place. The Edelbrock water pump i got was supposed to be for the Hi-Po K-code engine, the only one from them I could find at the time that was standard rotation without a backing plate. The original pump that I took off did not have a backing plate either

Head gaskets backwards were the first thing I checked.

Engine is only bored 30-thousandths over
I have a 3 row brass old school style radiator on my car. It is marginal for my stock 95 motor. I added a switch to be able to turn on the fan while in traffic since if I let the computer control it during that situation, the fan turns on at about 210 but the temp still climbs, reaching 220 before the fan is able to bring it back down to 190.

Since you have done some mods, I bet the radiator is simply not up to the task. Since you have a standard rotation pump, and you've done all of that other troubleshooting..........may be time to invest in a radiator that has more BTU killing capacity.

Edit: Just thought of something else. Check the timing. You mentioned it started to run rough when really hot. There is a process to setting the timing in these computer controlled cars. Sorry if I am telling you something you already know. Also, does the system ever pressurize? You mentioned it won't spew like the 289 did.
$400 and two radiators, not really looking for another one :/...kept the engine carbureted and still have the stock ignition, (well, stock distributor with pertronix ignitor), fuel isnt too lean and timing is moderate at like 6 I think is where I stopped backing it off. I had it at the spec'd 12 degrees, but backed it off at the suggestion of the forum.

And yes, the system does pressurize, takes a while for the hoses to get hard tho
another possibility is that the gauge is infrared thermometer can show the real temp of the motor
thought of that early on, but no, gauge is accurate...might do the reverse flush this weekend to see if it yields any results..
When I read 5.0 I assume it is fuel injected. Guess I need to stop doing that. :)
So are you saying the pump has an exposed impeller blade? I think you need a backing plate on the pump with an early style front cover.
I just looked at the edelbrock victor high-flow water pump on the Summit site and it looks like the 8841 pump fits the early small block Fords. It indicates that pump come with a backing plate, you may want to make sure you have the correct pump.
I'm not sure on the backing plate, because the original stock pump that came off the 65 289 timing cover did not have a plate, and it never had issues with heat
I just looked at the edelbrock victor high-flow water pump on the Summit site and it looks like the 8841 pump fits the early small block Fords. It indicates that pump come with a backing plate, you may want to make sure you have the correct pump.
There were two models of water pumps available for 65. The early pump is aluminum and has no backing plate. This is the style it sounds like the OP has. If so, then the 8841 is the wrong pump. He needs the 8842. The other model of water pump is cast iron with backing plate. Both pumps rotate the same direction but each requires a different timing cover. The cast iron pump will not fit on the early style timing cover due to the bolts that hold the backing plate on. Ask me how I know :grinroll:

OP, it sounds like you may have air still in the system some place. I kept having a ton of heating issues due to air in the system. it was a major pain getting all of the air out. Easiest way to get the air out is to just idle the car at a few hundred RPMs faster then normal. That helps get the car up to temps and circulate the water a bit faster and harder to force air out. Just be ready to pour more coolant in as it forces some to over flow sometimes violently.
Since the engine will run for a period of time before it starts running at too high temps., something must be moving around in the water jacket that's varying the way flow is circulating through the cooling system.

An old freeze plug that has been driven into the water jacket could be the cause. Just the plug being there may be enough to restrict the coolant flow more than it should be. If it's able to move around, the plug may be restricting even more.

The rag left in the coolant passage is another good possibility. I read where you said that the flow doesn't seem to be as good as it was. The mention of air being trapped is another. This is possible if the top of the radiator is sitting too low in relation to the engine. You did mention that the radiator isn't sitting in its original position, I believe.

When I put new coolant in my pony, I always "burp" it by squeezing the upper hose several times.
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