curtis75

I just put together a 427/390 engine with a roller cam and forged pistons. When driving it pumps coolant out the over flow (no catch can, its a '63) until it is too low on coolant and overheats. It has an aluminum water pump that is suppose to flow 30% more. I used copper head gaskets, new rad hoses, 160* stat. Any ideas? Thanks

midyearvette

what kind of sealer did you use on the head bolt threads??

rongold

What type of radiator are you using ??? Do you have a shroud ??? Is it sealed all the way around to prevent air from bypassing it ??? Are you running a distributor with a working vacuum advance unit, and is it connected to full time vacuum ??? Is that radiator cap in good working condition ???

curtis75

bolts were sealed with teflon tape, I have the stock big block rad, it has a shroud but isn't sealed. The distributor is a new HEI unit with a working vacuum advance. Haven't checked the cap yet I'll swap it with another car tomorrow.

When the coolant is full it runs at ~165 so I think the system can keep up, I dont think its a capacity issue.

JohnZ

Teflon tape works great on tapered pipe threads, but I've never seen it used successfully on straight machine threads; head bolts into water jackets need a non-hardening sealer like Permatex #2.

TXSTICK

Is that radiator cap in good working condition ???

wow

Sure alot of posts about this. Most of them mine. I found out that ignition timing and advance are the most crucial aspect in regards to overheating. When we first built my 427/435, I spent most of the first year on this forum asking about and checking posts on BB overheating. Someone told me to check my timing and advance and I was like WHUT??? Got it spot on and most of my overheating disappeaared. Still can't do a long parade in 90 degree weather, but as my builder says, "they don't call them HOT RODS for nothing." Good luck.

Westlotorn

Why Copper head gaskets? Copper is old technology and leaves a lot to be desired.
It sounds like you are pressurizing the radiator with compression leaks. Easy test to see if combustion is leaking into the radiator. All shops have tools to test this or you can buy kits at parts stores.
I would use Fel-Pro head gaskets, they have a full selection to protect you, choose based on your compression and Horse Power level. You will need to know the year of your block and heads to get the correct gasket. There is a good tech bulletin on this if you search previous posts.
Teflon tape on head bolts is a big no no. Threads should be chased to make sure they are free of any rust or other potential obstruction and when installed use a Head Bolt sealer as recommended in posts above.

MikeM

All I'll add is it's not the radiator cap! If the engine never gets over 165 with the system full, you don't even need a radiator cap.

It does seem like compression is leaking into the cooling system and pushing the coolant out. Take the water pump belt off, the thermostat housing off, top off the cooling system to fill the intake, start the engine and then watch for bubbles at the thermostat area.

midyearvette

this is why head bolt sealer is always my first question on these new builds....hopefully it's not the teflon tape although the symptoms sure point that way......

Kerrmudgeon

Depending on your heads, you may have needed to use a certain GM intake manifold gasket set. I'm learning quite a bit with this new 454 +.060 build. Aluminum heads call for this special set due to coolant distribution. I'm told without them, it will overheat.

And I agree with the copper gasket reply. Not the best choice, unless you want to cut the compression ratio down with a thicker than stock one.

racecar14

Ok, here is my two cents. I just finished a fresh rebuild on a 327. I had the same problem with overheating. Talking to an old gear head he said you have it timed too slow and or pre-loading the cylinders. I was 7 BTDC with 28 degrees total. He said time it at 12--14 BTDC with 35 degrees total. I was under the imppression that more timing produced more heat but after I ajusted the timing like he said it ran 175 degrees. Live and learn I guess. I hope it will fix your problem. It worked for me. Jerry

Vet65te

As Westlotorn mentioned in post #8, there is a kit you can buy that will show whether you have combustion gases in your coolant. NAPA Auto Parts might still carry this kit.

Mike T.

Derrick Reynolds

The way I think of it is that it takes a given amount of time to burn a given mixture at a given pressure at a given temperature to completion. The more retarded your timing, the more likely you are to push still-burning mixture up into your head and out into your exhaust manifold, causing a hotter head and exhaust, as opposed to letting it burn down in the cylinder where a larger amount of the energy will be used to push the piston down.

MikeM

I have seen engines running without bolt sealer. The symptom I saw was coolant coming out from under the head of the bolt, under the valve cover.

I'm not sure how combustion pressure would get in the cooling system past unsealed bolts. Seems like it would have to blow by the head gasket to do that. Head gaskets, in my experience generally blow between the bolt locations not at the bolt locations due to the clamping pressure at the bolts.

midyearvette

.....and i have thought over the years, how the hell does it happen?....you would think the head gasket would seal the combustion from the water jacket, but without a pliable sealer on the bolts, most of the time it will give a combustion leak in a cylinder or more than one bore
i have also seen what you describe, coolant leaking around the head bolts and no combustion gasses at all!...go figure
it's just always best to seal the open holes and still after all the years of engines, the old standby #2 as johnz suggests is the easiest, cheapest, and most reliable......jmo.....

curtis75

I guess I will do the head bolts again with sealer this time.

I used the copper gasket to get the proper quench number. I couldn't find gaskets thin enough (0.032 compressed height) that weren't copper.

I did replace the rad cap and it is better but still leaks a bit.

midyearvette

you can do all the head bolts, one at a time, torque each one as you go, just remove the exhaust manifolds and drain the coolant from the red, then remove the two rear head bolts on the lower set on each side and use a siphon hose to drain the block down an inch or so, clean the bolts, seal them with #2 and re install and torque....