I'm running the vortec heads and a shut off valve also, no problems, it runs cooler than the original heads. So I don't have a solution, only a doubt that the vortec heads are the culprit.

 

Huh - that got me thinking - if I remember - there were some guys on that thread that said the same thing. Some were running vortec heads and they were having problems , others weren't. I 'm not actually running a 'GM factory' head. I'm running an aftermarket Vortec head. Can't remember the name brand right now. Are you running GM vortecs?

 

Yes, I'm using gm heads. I guess yours could have a problem with the casting restricting the flow. Did you have the same problem with them on the 350 before the 383?

Just reread your post, same issue with both engines.

 

anyone really take a look at the factory valve and see if when closed it may have a port that allows water to recirculate?

Isn't this valve vacuum operated?

Neal

 

Heater cores and hoses are NOT there to cool anything.... period.... end of story. If it is overheating it is a coincidence, not the shutoff being the problem. If the heater core is acting like a radiator, the OP needs to find out what the cooling issue is in the COOLING SYSTEM itself, not the heater system. And no... the valve does not allow "recirculation" as that would circumvent the shutoff valve and its intended purpose.

 

I think he is referring to substitute 2 way valves that were used in different later applications. They divert flow before the heater core while still returning it to the pump.

I agree about the core not needed for cooling. something else is amiss. As far as I know there was no difference in the cooling passages in Vortec heads, just in the combustion chambers (heart shape). All 1st gen sbc that were not factory vortec engines had the coolant bypass hole in the pass side pump mount, so unless that bypass got blocked off with no holes in the tstat, problems may arise. Perhaps that's where all the results differ.

According to the avatar the OP has a BB anyway.

 

Just in case anyone is wondering where the bypass is in the pump ,here is a pic with the upper pump bypass blocked and the lower pic unblocked and the metal plug laying on top of the pump.

Noonie I thought he had 427 SB.

 

Good pic.
I know there is some confusion between the BB and sbc bypass.
Also, some of the aftermarket high performance pumps don't have that bypass hole at all.

Ya, it looks like he has a small block 427.

 

Roger - I got to say it man - You are absoultely amazing with those pictures of yours. It doesn't matter what problem we have out here in forum-land , you seem to have a picture to help explain to the masses what we're all talking about ! Me - if I had to come up with a picture of my son - ANY picture - (and he's 21) , let alone a picture of a water pump - I'd be hard pressed to do it. You rock my friend.

 

Thanks, I do run to the garage a lot to take pictures,my girlfriend thinks I'm nuts,especially when its midnight.

 

noonie is correct you have completely missed what I was getting at.

I don't have a factory valve to look at but was hoping that some one out there may. I'm curious if this valve may have a port in the valve barrel that may allow the water to re-circulate back to the pump to prevent cavitation.

If the OP is running a high flow pump and has stopped the flow of water to the heater core than with the water pump dead headed and no flow at the T-stat the pump can cavitate and loose system pressure. Two critical functions of the cooling system are flow and pressure. You have to have both for the system to function correctly.

The internal bypass may not be sufficient to supply a high flow pump with the needed flow to prevent loss of pressure and flow.

If you think about it when the T-stat is closed the majority of flow is through the heater core and the bypass. Without the flow through the heater core or if the shut off valve has a re-circulation port and its replaced with a ball valve than all that is left is the bypass. The bypass alone may not be sufficient to allow enough flow for the pump.

The bypass hose on a BBC is placed such that the flow is at the T-stat and is a good size hose and fittings that will allow a good bit of flow. When I block mine off on my BB the temps will swing drastically and when I re-install the bypass hose the temps settle down.

I've herd of people removing the bypass hose on a BB and not having any issues, the only thing I can come up with is I have a Stewart stage 4 pump and it needs the large bypass to prevent loss of pressure and flow.

Just something to think about

Neal

 

In the first place you don't need a heater and many early vettes were produced without one and never were there any cooling problems from its omission......If more people would leave the cooling systems alone and quit trying to out engineer the engineers with highly advertised aftermarket parts their cooling systems would be OK

 

If less people tried to out engineer the engineers - all we'd have is a bunch of people driving old cars. What fun would that be. Thats no hobby.

 

I am actually an engineer, and I have learned one or two things and found one or two design flaws shice my 68 was built 43 years ago.

But, since the topic is overheating and temperature rise when ONE line is bolcked, and the symptom dissappears when the line is UNblocked, and the cooling system was not problematic prior to this single change, lets help this guy troubleshoot his problem.

My suggestion would be to eliminate the heater flow loop by connecting the return to the heater feed at the water pump. YES, the hose sizes are different. This is a test.

Does the overheating remain?


Also, please make certain there is no airlock in the system. The BEST way to eliminate airlock is to run the car at operating temp with the cap off the radiator or overflow, depending upon your radiator/year/ etc. As the water level drops i nthe radiator, add more.

Since I'm not there, I won't "bet" what the problem is. But I'll help troubleshoot.
D

 

one thing being missed is coolant capacity, with the heater core shut off there is about a quart of coolant not cooling. i like the concept of a bypass don't know if that would fix your problem but it should be easy to find out.

 

I havent messed with the shut-off valve since my last post... Ive just dealt with the extra cabin heat. At least the weather is cooling down now.

As far as the rest of my setup, (unfortunately ) I do not have a 427 small block. Just a nice built up 350. The heads are AFR 180's.
I only had the engine builder put the short block together. I put the heads and water pump back on and I didnt change anything on them. The water pump is the same cast iron one that was on the car when I bought it, so its probably pretty old. If I end up picking up a new water pump, Ill close the valve again and see what happens. Until then, its staying open.

 

That would be the same as not ordering a heater and those Vettes didn't overheat and most of those were southern cars or a hot climate which would be in hot conditions all the time.......

he has something else causing the situation

 

Well - looking at it logically , I don't think you need a new pump. Your system is like mine (somehow).

Valves open: gauge? 180
cabin heat? LOTS and LOTS
outside temp? +90 degs. Rad working (thanks DeWitts)

Valves closed: gauge? 180 climbs to 240 , drops to 180 , climbs to 260 ! , drops to 180. Over and over and over !
cabin heat? None. Nice and cool.
outside temp? whatever. 50 - 70 - 90 .

Valves closed + bypass open:
gauge? 180 (rock steady)
cabin heat? none.
outside temp? +90.

What do we know? Pump HAS to be working. I've driven the car in January and I know that heater core pumps out all kinds of heat so the pump HAS to work. If the pump wasn't working , the heater core would get cold pretty quick when its -30 outside. It has to be something with the aftermarket heads. Guys do this mod all the time with the factory heads.

What is it exactly - I'm stumped. But I don't think its the pump.

* If you do end up changing out the pump someday though - and it fixes it , can you send me a PM ?

 

Vette427................mine does exactly the same thing as yours. I have a 350 w/Brodix heads and it'll scare the heck out of me how fast the temp gage goes up. Usually happens when I first start driving it but it almost immediately goes back down to 180 or so especially when I gun the engine a little. I also have a De Witt radiator. I've come to the conclusion that it really isn't overheating as the gage says, I think somehow an air bubble or pocket is being formed because of the location of that shutoff and it finds a home near the temp sender but it defies logic, I know it doesn't make any sense. As soon as I open the shutoff it'll never do it again. I've felt the hoses radiator and intake when this happens and it does not appear to me to be overheating.

I think 68sbcoup has the best idea about replacing the heater lines and shutoff's with a loop as a test. I always wanted to try that to see if corrected the problem.

Not sure how long yours lasts but mine doesn't stay up there very long and it comes right back down. Once in a while it'll do it on the highway but it doesn't last long. I've changed thermostats and all that too. If you happen to have an IR gun it would be interesting to check the temp to see if it really is overheating or it's just the sending unit.

Where is your temp sending unit located? Mine is in the intake next to the gooseneck.

 

Mine is also located next to the gooseneck.