I got my car alittle over a year ago and not knowing when the previous owner did any cooling system maintenance I decided to just flush the whole system out. When I took off the thermo housing there was no thermostat in it(hoping this is not a sign that the previous owner was having overheating issues!). So being that it is mainly a street car, I want to put a thermostat in but I have a few questions before I attempt it:

1) Do all water pumps on small blocks have an internal bypass? If not is there a way to recognize an internal bypass water pump from one thats not, so I know what I got? Don't want to put a thermostat in before I know if its internally bypassed so the engine coolant can circulate before the thermostat opens! I can imagine the consequence of no flow is not good!

2)Which thermostat and gasket would you recommend for a 383 street motor with around 400hp? The intake I have is an Edlebrock RPM Aig Gap #7501. I searched on here and read some mention the Robert Shaw(Autozone carries it) #330-180 & a Felpro gasket #35062. Would these be the best ones for my setup? The thermostat housing has a rubber o-ring in it but I might pick up the gasket anyway as cheap insurance incase it leaks.

thanks for all the help, I just hope running a thermostat this summer doesn't show why the previous owner didn't install one!!!!!!!

The bypass for a SBC is the little hole on the block/water pump on the pass side.
Thermostat would be a high flow unit, 180°, like Mr Gasket MRG-4864.

If housing has an O-ring, and the manifold is flat, check with straightedge, then the O-ring is the only sealing item needed. Otherwise, buy a new alum hsg, no chrome, and use a new gasket. use anti-seize on the bolt threads.

Thanks Everett

Is this little hole(bypass) internal behind the pump? I don't see anything that could be external like on a big block. Do all small block water pumps have an internal bypass? Just trying to confirm there is a bypass before I put in a thermostat. thanks again

Thanks Everett

Is this little hole(bypass) internal behind the pump? I don't see anything that could be external like on a big block. Do all small block water pumps have an internal bypass? Just trying to confirm there is a bypass before I put in a thermostat. thanks again

If it's a belt driven waterpump it should have the water bypass. If it ever had an electric pump it would have been plugged. Yes it's internal between the waterpump and block.

i think the only small block water pumps that didn't have the bypass were on the 96-99 vortec motors. those blocks also aren't drilled- so unless you've got a vortec block, then i wouldn't worry about it.

great, thanks for your guys replies.

Yep, its an older small block(not sure what year yet, still have to get that decoded) that has a belt driven water pump. So I will try putting in a thermostat now that i know it has an internal bypass and see what happens, thanks again