Overheating... SBC 350

[jackbrad]

I should have a new set of answers tomorrow on this issue. I have been out of town but, I think my parts came in today according to my wife.

 

[jackbrad]

I wanted to post up that I did the bypass hose on my vortec heads and it seems to have made a difference. I did a bunch of research when I put the heads on and read many many posts about they were bolt up and no mods needed other than a manifold.

I've since found the bypass hole thing and found the water pump is not as long as a non-serp, non-votec long pump and is needed if you run the serp belt system with the vortec heads.

I do run a ball valve in my heater hose so that may make a difference too, although both heater hoses come off the water pump.

I don't actually understand the need for the bypass hose? Why is it needed. I used a long water pump with my serpentine belt kit.

 

[tawright]

I don't actually understand the need for the bypass hose? Why is it needed. I used a long water pump with my serpentine belt kit.

As I noted on Post #14, I discovered that when I put a new motor in that had Vortec heads, I started having overheating problems that did not exist with my older SBC350. After googling the problem, I came across several threads under "SBC Coolant Bypass" about the need for adding a bypass when using Vortec heads. Once I added a bypass by adding a "T" in my hose down to the manifold, I have not had an overheating problem since.


http://s1081.photobucket.com/albums... Items/?action=view&current=coolantbypass.jpg

 

[AdamKFarmer]

Just want to throw my 0.02 in here that PV=nRT is the ideal gas law, and has to with "ideal" gasses and has little do with a binary (water and EGL) system with mostly liquid and some gas in equilibrium. What you can really look at is a phase diagram for EGL and water and observe that as pressure increases the phase changes from gas to liquid, if you keep increasing it it eventually forms a solid! All types of matter do this.

 

['74 UA FJ]

I have vortec heads and don't have a T as posted above. My temps stay 185-195 all day long, and have for 10 years.

 

[chevurai]

If you don't know if the heads have an internal bypass adding one will do no harm.

 

[tawright]

I have vortec heads and don't have a T as posted above. My temps stay 185-195 all day long, and have for 10 years.

Fair enough. However, it is quite possible that the intake manifold does not have a coolant buypass, which I believe to be the case in my situation.

 

[jackbrad]

OK... wanna know what my issue was?

I figured it out yesterday.


Blown Head gasket.

Yep.

Between the number 3 and 5 cylinders the head gasket failed.

Coolant was going in the cylinders and combustion gas was going into the cooling system..

I found it by removing the spark plugs. I found one with coolant burnt on it. After removing the head we saw burnt coolant all over the combustion chamber and the head gasket failure.

I am in the middle of putting everything back.... Ill let you guys know how it behaves after we reassemble the block.

 

[jackbrad]

Fair enough. However, it is quite possible that the intake manifold does not have a coolant buypass, which I believe to be the case in my situation.

I have the stock manifold for the vortec heads but, I will look and see if the bypass is there.

Thanks for the clarications

 

[Pierps]

Yikes. That sucks man, but I'm glad you found the problem.

 

[miker]

Optimal cooling is with 6 to 8 cubic feet per second. If the rate is increase to 10 cubic feet per second or more, several problems crop up. Foaming and aeration of the coolant is one.

...Let's assume it is designed from the factory within the optimal flow rate of 6 to 8 cubic feet per second.

...Now the optimal flow rate may be at the low end, like 6 cubic feet per minute, or even lower, less than optimal.

All interesting reading in this thread, even some of the BS.

But, I just don't think these numbers are possible with an automotive type water pump:
6cf/s = 44 Gallons per second or 170 liters per second
8cf/s = 60 Gallons per second or 226 liters per second
10cf/s = 75 Gallons per second or 283 liters per second

 

[jackbrad]

Every thing put back correctly ... and still overheating.

It is not irratic like it was and there is no doubt I had a head gasket issue but, the overheating still occurs.

Driving around the neighborhood... everything is fine. Engine runs at 200 which is exactly where I expect to see it.

Get out on the highway over 55 for about 2 -3 miles and the temps creep up to 230. I turned at that temp because I cant stand another head gasket blow.

The only thing that I can figure is there is some issue with the configuration of block, head intake or intake gaskets.

I have 1995 Vortec heads, and older 350 block design (purchased in 2007 as GM performance crate engine), stock intake manifold design (1995 chevy g20 van)

This is getting ridiculous.


I am now taking tawrights information on a bypass hose much more seriously. But the information out there is not very complete.

Here is what I think I know.

Late 95 -2000 vortec heads did not have a coolant bypass cast into them. This bypass allows some circulation of coolant until the thermostat opens the system fully.

In a Vortec, a bypass hose was used to fullfill this requirement and it ran from the front of the intake to the top of the waterpump.

Here is the thing... My intake (which was stock off avortec engine) does not have the port for a bypass hose on the front. There is a port on the water pump however

Stumped.

 

[swapwap]

Well, I have an sbc. 350/290hp crate motor, those older motors run 200-230 degrees, that's just how they run, im sure putting the votrec heads make it run hotter with my hp. even with a hi flo water pump, 4 core alum exc. mine will get hotter if I sit in traffic or still for awhile. I put an aux 2100cfm fan that kicks on at 190 and pretty much runs all the time while I drive. With this I never get to 210 or higher. Don't know if it will help but for about $50 and some time it might help you out. I know many cars today are cooled by these aux fans and don't have water pump fans anymore.

 

[jackbrad]

I am 90% sure now however that i dont have vortec heads.

 

[fieldsken1]

Put a hiph flow thermostat in it. It's o ly 13 dollars and real simple

 

[jackbrad]

Thanks, I did add a high flow thermostat.

 

[kulangot]

Have you checked your lower radiator hose to see if it is collapsing under high flow and restricting water? Get one with a spring it it. That has gotten me before...

Have you also made sure that you don't have any air in the system?

Last but not least, I once took apart a motor because of a bad timing light and replaced a bunch of cooling parts because of a bad temperate gauge. Check all the basics!

My V8 truck ran best with a large mechanical fan and fan shroud.

 

[Bret]

I wish you were closer, we could start swapping parts from truck to truck till the problem went away. Finding a definitive solution would be helpful.

Fwiw 383, Dart Iron heads, Summit hi-flow water pump, miloden hi flow thermostat with small hole drilled in it, 7 blade 18-19" clutch fan, 19x26 Al 2 core Rad and it will sit within 3 degrees of the thermostat in the Florida heat on I95 doing 70.

The fand and shroud made the biggest difference overall.

 

[jackbrad]

... I know one thing. I need a set of new ideas

 

[GLSisk]

I was having the same issue with mine a couple of years ago; turned out that part of the problem was that the timing chain had stretched slightly (over 100k on the motor) and that jacked with the timing. I had a decent radiator and good electric fan, but as the RPMs increased, the timing on the motor would jump around a bit.

I disagree with electric fan=overheating comment. I'm now running the biggest radiator I could squeeze in there (all aluminum from Speedway, cost about 150.00) and an electric fan out of a Lincoln MK VIII. There's a speed shop out in LoCal that sells the fans for about 80.00 complete with shroud. I live in Texas and you know it gets hot here; I've had zero probs since the timing chain/radiator/fan additions. at PM if you want and I'll try to find the number of the place where I got the fan. Good luck.