BBC thermostat bypass

[RedRacer]

When building a street BBC, using performer RPM intake and a stewart stg1 water pump, should we keep the line that goes from the water pump to the intake manifold, and what is that line for... to keep water moving in the heads when the thermostat is shut? Thanks, Red

[bill jones]

-if you were to plug off that hose and still run a thermostat you'd have to drill some holes in the flange of the thermostat so that water has a place to flow while the termostat is closed.
-All the water that runs thru the bypass hose is doing virtually nothing towards cooling of the engine as that water is like a big leak and never actually goes to anywhere inside the engine that really counts.
-If you do eliminate that hose---and decide to drill holes in the T-stat flange---I'd recommend that you make an aluminum or brass tag with notes to drill all T-stat flanges----and attach that to the T-stat housing bolt so that you don't inadvertantly forget about it.
----------------------------------------
-Personally I'd plug the bypass and drill the flange and tag the housing especially if you are up against a hard to keep it cool situation.
-For holes I use at the most six 3/16".
-The inside diameter of the bypass hose and fitting is approximately a half inch which is .196 square inch of area.
------------------------------------------------------
-Six 3/16" holes is only .164 square inch area and six .203" holes (the next size above 3/16") is .194 square inches of area.

[SupStk]

Bill is correct in everything he stated. I wanted to remind you that when the thermostat is closed the bypassed water is being returned to the engine to help reduce warmup time. If the cooling system is too efficent, with drilled thermostat flanges, the the engine will be slow getting to operating temperature especially in cold weather. Too bad more engines didn't adopt the same system that HD truck BBC's had. When the thermostat was open the bypass water was shut off.

[rebelyell]

Bill is correct in everything he stated. I wanted to remind you that when the thermostat is closed the bypassed water is being returned to the engine to help reduce warmup time. If the cooling system is too efficent, with drilled thermostat flanges, the the engine will be slow getting to operating temperature especially in cold weather. Too bad more engines didn't adopt the same system that HD truck BBC's had. When the thermostat was open the bypass water was shut off.

OE GM iron head Vortec L31 vin code R (350) and L30 M (305) motors in '96-'02 light to medium duty GM truck have functionally quite similar system. Their OE lower intake manifold has a lower seat and a bypass hose to pump. Its T-stat has two gate valves --- one in conventional position at flange but another about two inches below which moves in conjuction with upper but mates with seat cast into lower intake manifold. Works like a champ and as it should.

GM 131-151

[rgalajda]

In reference to a true street car.
All engines that run a thermostat need to have some type of bypass provision to avoid localized hot spots, minimize the chance of steam pockets developing, promote even and rapid warm-up, and prevent water-pump cavitation. On some engines, such as classic Chevy small-blocks, the bypass is internal; on others, such as your big-block Chevy, the bypass is external.

Stewart Stage 1 water pumps have a bypass. Not all Stewart pumps do. I have used this pump and found no advantage blocking the bypass and drilling the thermostat. The down side can be slower warm up times even in warm weather.Why would you want that? Just use the bypass.

More important is to use a high flow thermostat such as the Robertshaw shown below. This enhances the performance of the cooling system. Even a new thermostat should be tested, before installing, for accuracy of opening. I've had a 180 thermostat that opened at 155 degrees. The temperature gauge should also be tested for accuracy. For a mechanical gauge just immerse the probe in hot water with a reliable test gauge .
Remember that the probe has to be installed protruding into the coolant, not blocked by an adapter fitting.

[Tom68]

Stewart Stage 1 water pumps have a bypass. Not all Stewart pumps do. I have used this pump and found no advantage blocking the bypass and drilling the thermostat. The down side can be slower warm up times even in warm weather.Why would you want that? Just use the bypass.

Why, because then there is no radiator bypass (just drilled thermostat through flow), warm up is slower, the whole system comes up to temp, and when things get tough all the coolant has to go through the radiator.

Bypass cooling systems should be done properly like Clevelands were and LSs were. SBCs were a piss poor bypass design.

[rgalajda]

Stewart Stage 1 water pumps have a bypass. Not all Stewart pumps do. I have used this pump and found no advantage blocking the bypass and drilling the thermostat. The down side can be slower warm up times even in warm weather.Why would you want that? Just use the bypass.

Why, because then there is no radiator bypass (just drilled thermostat through flow), warm up is slower, the whole system comes up to temp, and when things get tough all the coolant has to go through the radiator.

Bypass cooling systems should be done properly like Clevelands were and LSs were. SBCs were a piss poor bypass design.

Not sure if i understand . You agree with using the bypass hose or disagree?

[rp930]

Even a couple of 3/16” holes make it slow to warm up. I would run the hose.

[Tom68]

Stewart Stage 1 water pumps have a bypass. Not all Stewart pumps do. I have used this pump and found no advantage blocking the bypass and drilling the thermostat. The down side can be slower warm up times even in warm weather.Why would you want that? Just use the bypass.

Why, because then there is no radiator bypass (just drilled thermostat through flow), warm up is slower, the whole system comes up to temp, and when things get tough all the coolant has to go through the radiator.

Bypass cooling systems should be done properly like Clevelands were and LSs were. SBCs were a piss poor bypass design.

Not sure if i understand . You agree with using the bypass hose or disagree?

Depends what you're doing, they do allow water to bypass the radiator when the thermostat is open, so you wouldn't run it if your struggling with overheating.

[Geoff2]

Another important function of a bypass is in case the stat jams in the closed position. THAT is THE reason why a drilled stat is used with pumps like the Stewart pumps that deleted the bypass.

[rgalajda]

Struggling with overheating is no reason not to use the bypass hose. Find the reason why your cooling system is not up to par. Don't understand why people try to reinvent the wheel with hacks.

[Tom68]

Struggling with overheating is no reason not to use the bypass hose. Find the reason why your cooling system is not up to par. Don't understand why people try to reinvent the wheel with hacks.

People do whatever, manufacturers make up for their cheap historical engineering by improving it, BBCs and SBCs had equally poor bypass systems.
Racers quick fix was to block the bypass and run either a restrictor to raise block pressure or a drilled thermostat to do the same ting with a quicker warmup.

Clevelands had a good bypass system, 5.7 Vortecs had a good bypass system, LT1s had a good bypass system, LSs had a good bypass system, SBCs and BBCs had a poor system that required modifications for acceptable performance with high horsepower engines.

There's no reinventing, just making cheap systems work.

[rgalajda]

Restrictors
Years ago, cars used low pressure radiator caps with upright-style radiators. At high RPM, the water pump pressure would overcome the radiator cap’s rating and force coolant out, resulting in an overheated engine. Many enthusiasts mistakenly believed that these situations were caused because the coolant was flowing through the radiator so quickly, that it did not have time to cool. Using restrictors or slowing water pump speed prevented the coolant from being forced out, and allowed the engine to run cooler. However, cars built in the past years have used cross flow radiators that position the radiator cap on the low pressure (suction) side of the system. This type of system does not subject the radiator cap to pressure from the water pump, so it benefits from maximizing coolant flow, not restricting it.

Any aftermarket thermostat housing that mounts the radiator cap directly above the thermostat location, or that mount the radiator cap in the top coolant hose, are NOT recommended. Both of those housing styles are poorly designed, and will push coolant out of the cap at high RPM.

A common misconception is that if coolant flows too quickly through the system, that it will not have time to cool properly. However the cooling system is a closed loop, so if you are keeping the coolant in the radiator longer to allow it to cool, you are also allowing it to stay in the engine longer, which increases coolant temperatures. Coolant in the engine will actually boil away from critical heat areas within the cooling system if not forced through the cooling system at a sufficiently high velocity. This situation is a common cause of so-called “hot spots”, which can lead to failures.

In a cooling system, a higher pressure equates to a higher boiling point for the coolant. Higher coolant pressures also transfer heat from the cylinder heads more efficiently. You can use a radiator cap with the highest pressure rating that the radiator is designed to accept. In general, performance radiators will accept 22-24 PSI, and professional racing radiators will accept a 29-31 PSI.

[Tom68]

Restrictors
Years ago, cars used low pressure radiator caps with upright-style radiators. At high RPM, the water pump pressure would overcome the radiator cap’s rating and force coolant out, resulting in an overheated engine. Many enthusiasts mistakenly believed that these situations were caused because the coolant was flowing through the radiator so quickly, that it did not have time to cool. Using restrictors or slowing water pump speed prevented the coolant from being forced out, and allowed the engine to run cooler. However, cars built in the past years have used cross flow radiators that position the radiator cap on the low pressure (suction) side of the system. This type of system does not subject the radiator cap to pressure from the water pump, so it benefits from maximizing coolant flow, not restricting it.

Any aftermarket thermostat housing that mounts the radiator cap directly above the thermostat location, or that mount the radiator cap in the top coolant hose, are NOT recommended. Both of those housing styles are poorly designed, and will push coolant out of the cap at high RPM.

A common misconception is that if coolant flows too quickly through the system, that it will not have time to cool properly. However the cooling system is a closed loop, so if you are keeping the coolant in the radiator longer to allow it to cool, you are also allowing it to stay in the engine longer, which increases coolant temperatures. Coolant in the engine will actually boil away from critical heat areas within the cooling system if not forced through the cooling system at a sufficiently high velocity. This situation is a common cause of so-called “hot spots”, which can lead to failures.

In a cooling system, a higher pressure equates to a higher boiling point for the coolant. Higher coolant pressures also transfer heat from the cylinder heads more efficiently. You can use a radiator cap with the highest pressure rating that the radiator is designed to accept. In general, performance radiators will accept 22-24 PSI, and professional racing radiators will accept a 29-31 PSI.

and yet many OEMs are running top tank caps and working perfectly, don't believe everything company's selling to you have to say.