Hey guys -- trying to finally finish my "covid project" (a bit late I know haha). Its a 68 with a 396. I redid the entire car including engine work (stripped down to short block... checked bearings, replaced all gaskets, cleaned the heads, etc...). Its working, for the 1st 5 minutes -- it eventually gets hot, and goes over temp. I have Dakota Digital gauges, and they are reading 223 when my alert goes off. I have an upgraded champion radiator with a 16" electric fan that I believe comes on between 180-190*. Thermostat is a gates 33008s which should be a 180* t-stat (pretty sure I drilled at least 1 hole in it for air bubbles). I also upgraded all my front components incl the waterpump (see pics).

I went to squeeze the upper hose and it was solid, so I figured there was trapped air in the system. The coolant in the overflow was cold. Both hoses were warm so Im assuming the t-stat is working properly. Then I started seeing smoke from the vent valve on the pass side (see vid) -- assuming this isnt normal haha. Also heard a bit of pinging from the engine at this point, and turn it off (you can hear it in the video)

Sorry for the dirty/ junky engine bay. A lot of stuff it still temp zip tied and dusty until I can give it a final clean up!!

Questions:
Is there a trick way to get air out of the system that I dont know for these engines? Seems like it should be pretty straight forward.

I dont have that bypass hose on the top of the waterpump to the intake manifold. I think I read last year that it isnt necessary -- I couldnt find a flange to get it at an angle that would work. Do I need this?

Fan too small? I dont think so, but I guess its possible. Im also not running a shroud at this time. The OEM overflow tank was in a weird position so I upgraded it to a smaller one, but put it in a more convenient location. The coolant wasnt getting to it until I opened the radiator cap, then it would finally flow to the overflow. Not sure why this would be the case --

Theres no oil in the coolant or coolant in the oil, I don't think it could be a headgasket issue -- it was newly replaced and dont see any signs that that would be the case.

Any other ideas would be welcome!

Video of the car running" target="_blank">Video of the car running

overall view

waterpump -- no bypass

rad/fan

new overflow

 

sounds healthy

I like by-pass hoses.

as long as pump is spinning in correct rotation and thermo is opening fully,
its hard to pinpoint.

using heater will give an idea of water flow and temp by grabbing the hose/s.

wrong head gaskets not ling up with holes from block to head?

you need to verify water is flowing from pump to block to heads to in-take to upper rad.

sometimes you can feel flow in hoses.

there, a start to thread has happened

.

 

I wouldn't consider that smoke coming out of the breather and with no PCV valve is the other valve cover its just venting. The Fan hooked directly to the radiator with no shroud is never going to work but you won't find that out till you start putting a load on the engine. I wouldn't believe any new gauges till they can be verified with a Temp Gun. And a temp gun is where I would start diagnosing what's going on. I would check the thermostat housing to see when it opens. Along with every other component of the cooling system I'd be willing to bet your going to find out its not as hot as you think.

 

i have a list of things for you to check
Is the Dakota Digital gauges using their own sensor? I have their fan controller and it says that their gauges need their sensor.
Have you used another way , mechanical gauge or and infrared heat gun to verify the temp?
Does the lower radiator hose have a spring in it, doe sit look like its collapsing ?
Who made your water pump? can you verify the part number has the pump designed to spin clockwise versus counter clockwise for newer motors that use a serpentine setup?
Dont worry about air bubbles, its a forced system with the pump. Once you drive it up a hill if there is an air bubble it will sort it self out. I have never, never, never had an air bubble issue. Just doesnt make any sense in these old motors versus the newer designs without caps in the radiators...
Your motor shouldnt get that hot in 5 minutes without a circulation issue. My 427 takes twice that to get up to temp.

When you had the block apart did you blast out the water passages and take out the freeze plugs to clean out around the cylinders?


also
You will need a fan shroud that will bring that cooling fan away from radiator and will allow the fan to suck air though the entire surface. Without it when you get in hot summer traffic you will over heat fast. Your setup would be fine on a highway or cruising country roads but any traffic will make it heat up fast. That fan will only draw air through that small openning. And make sure you have all the radiator seals in the forward radiator compartment and around the radiator and radiator support or it will run hot while cruising as well.

also you should consider a bigger air dam than the stock tiny one for the 68

I added a bigger one that resembled the 71 extension that GM added to help cooling. Eventually I got a fiberglass dam

 

I checked the HG when I installed it. Everything looked like it lined up. I think I took pics too, I'll double check.

I'll check flow as well

I'll use the temp gun to verify. Is there any place in particular I should be pointing it?

-The DD gauge is theirs that came with the kit.
​​​​​​- I'll double check with a temp gauge. As of now just the DD gauge and the on/off temp of the fan as a loose measure
-it has a spring on the lower hose, so no collapsing. It's just under pressure like the upper hose. It gets really hard, like it's ready to pop
-i can try and find the part# for the wp. That the alternator and a few other items all came together as a chrome kit. But wouldn't the WP just spin whichever way the engine was spinning? I don't think it had any special internal features that would reverse the flow.
-it was maybe 10-15 min haha I think I exaggerated
-it flushed the coolant but didn't take out the freeze plugs. You're thinking there could be a clog?
-do you think I should have went with 2 smaller fans vs the one 16? Or maybe an 18 or 20"? Not sure what the biggest one is that would fit. I'll look into the shroud though. Thought I could get away without having one for now 😩
​

 

I used a single 16 inch for quite a few years. It worked fine but was really loud.
When you look at shrouds i think i found my first one at Jegs. You cut the center hole yourself. It sat just over an inch from the radiator so it got good volume.
The water pumps have fins that force the water the way they are designed. If it was all in one kit it is probably a clockwise designed pump.
Yes the block could be full of sludge. If you can get one of the block plugs out it should shoot out of the block....when i pulled my 396 plug i had to use a punch to get through the rust.....
Verify the temps with a heat gun and go from there. Fords have diectional head gaskets, havent seen one for a big block chevy but who knows. Whats your timing set at, maybe back it off and see what happens. What type of cam are you running...hydraulic or solid

 

Thinking more into it you should eother put a big fan in front of your car and nlow air into the radiatot or take it for a cruise above 40 mph and see what happens. It could just be because your in the garage and your fan isnt doingnit because of the shroud

 

It doesn't sound right saying the hoses are ready to burst. Could there be a plastic plug in the new Radiator?

 

When I had the heads off I could see the coolant still in the block. It was green green, no signs of sludge... Of course it could be all the way at the bottom I suppose --

Where should I point the gun to get the most accurate temp?

I haven't checked timing since last year, I'll have to verify it again tomorrow.

Cams are solid, OEM style I'm supposing. It's the one thing I never took out to look at. I was going to upgrade it but wanted to stick with basic stuff 1st just to get the car running

Thought so, but it was outside haha. Cool day today, maybe 60s

Plastic plug in the inlet outlet? Shouldn't be. They came with red external caps you had to take off before putting the hose on them.
When I ran the car last year I didn't have this issue. It only started when I added my aftermarket reservoir for some reason.

 

For infrared readings the radiator hoses are a good indicator. Depending on the gun the sensor may give different readings if the surface is reflective. I find the upper hose is easy to get to and gives the outgoing fluid temp. the front of the upper intake manifold where the crossover is is easy to get to as well. Maybe the front of the heads if you can get to them.

 

Lotta good suggestions above on things to check.

My personal opinion, seriously consider connecting the bypass/recirc hose at the intake and water pump (although it doesn't look like the pump has the normal location for a hookup). The bypass allows an adequate amount of water flow inside the block while it's warming up, for better heat distribution.

 

OP, you stated you didn’t have this overheating problem last year and the overheating just started this year after you changed to the aftermarket reservoir?
Is the reservoir cap vented and is the water in the reservoir under pressure?
Not that it’s the problem, but if the overheating started only after you added the reservoir, then try disconnecting it and see if the problem goes away going back to the oem reservoir.

Did you just do the engine work this year?

Where is your vacuum advance to the distributor hooked up?

I would double check that you used the correct head and intake gaskets.

It is somewhat common for a new thermostat to malfunction.
If it isn’t opening, this could be causing your overheating issue.
Try removing the thermostat and see if the overheating goes away.
If so put in a new one and be done.

 

It is possible to check the thermostat without removing it.
Remove a little coolant from the radiator, just enough to see the fins inside.
When the engine is cold, start it up without the radiator cap on.
You shouldn’t see any water flowing through the radiator, or you may see slight movement.
When the water gets up to temperature the thermostat should open and you will see the water flowing rapidly through the radiator.
If this doesn’t happen swap the thermostat and try it again.

If you run the engine without a thermostat you should see rapid coolant flow through the radiator even when the engine is cold.
If you don’t see movement you have a blockage somewhere, or as stated above a reverse rotation water pump.

 

I was excited to come here and tell you guys I figured it out... But you stole my thunder haha

I decided to disconnect the reservoir and drain it. I only filled the radiator and let it run. It seems like the coolant in the reservoir was creating a pocket between the radiator cap/overflow tube and the overflow reservoir, and the air couldn't get to the reservoir.
I redid my timing (14* at idle, 36* @ 2800 -- both with the vac advance on) which took maybe 10-15 min. I went back and looked and the temp gauge was dead in the middle. Checked my DD gauges and it read about 185 or so, and my IR temp scanner read about 188 where my electric fan cut on sensor was getting it's reading, so I think we're good!!

If I go to start it and have the same issue again, I'll chime back in, but I want to thank everyone for the quick and informative help! Maybe I can finally drive the car this year haha!!

 

Thats a new one...congrats on figuring it out

 

Haha yeah 1st for me too! Appreciate your help!

 

You check and set timing with the Vacuum Advance unplugged......when plugged in it should be on full manifold vacuum.....

Jebby

 

You don't check timing with the vac can connected. Unless your checking how much timeing your vac can is putting in. Unplug the vac can and plug the hose. Set timing. Then make certain the vac can is connected to manifold, not ported vacuum. Then you can recheck and see how much timing your vac can is adding in.

 

Correct, that's how I did it -- was just stating the overall, with the vac hooked up afterwards!

 

Cool....a closed chamber 396 like your will probably want 38 degrees total.......so just keep that in mind.

It is amazing what proper timing does to cooling in an engine......especially these Vette's with the cramped engine bay......not only does it directly effect temperatures in the coolant....it indirectly heats everything up outside the engine due to elevated EGT's.....

Jebby