350 cooling problem

[4x4 VanMan]

Hey guys, I could use someone else's brain muscle on this chevy 350 cooling problem I'm having. It all started after buying a safety thermostat after noticing it was running a little hot 210-220 but not ever boiling over. Put in a 160 safety stat and drove it for a couple months that way until I noticed it started barely getting up to 160 temp and was running more like 140 most of the time. Pulled the t-stat and it was stuck open as designed so I threw in a 180 normal t-stat. Now it makes this water hammer gurgling noise after about 5-10 minutes of running has blown off the upper radiator hose if I try to drive it, kind of like if it's a stuck closed thermostat.I have tried several other t-stats from different places with the same result.
So now I take the heads off the motor thinking head gasket, or something else, even though it passes a block test with no HC in the coolant. Take my summit aluminum heads with less than a thousand miles on them in and have them checked for cracks which come out ok. The gaskets looked fine, but the bolts seemed loose when removing the heads so I chalked my problem up to the Chinese head bolts I was using. Throw the motor back together with ARP bolts and steel head gaskets and I still have the exact same problem. If I put the open t stat back in it runs great, doesn't overheat, but it does start running super rich at 140 degrees.
Am I the unluckiest guy at the auto store and can't get a working stat or is there something I'm missing. Took my water pump apart and the impeller is fine and correct direction pump.
The engine in question is a older 4 bolt block, 200cc aluminum heads, Procomp Rpm air gap manifold, headers, RV cam.
One thing I have noticed is that this style of intake has the groove machined into the head for the longer newer style GM thermostats with the rubber ring, I'm running the older shorter style of t-stat.

[97cargocrawler]

T-stat in upside down? Water pump rotating in the correct direction? I dunno. I have a lame 4.3.

[Sailing_Faith]

Two ideas,

Take both thermostats, put them in a pan of water and boil them. See what they do. Then get another one, (maybe the long stem) and do the same thing. Install the one that opens where you want.... I suspect you have two bad thermostats....

The other idea, which I have no ideas why this works but it has for me,,, I drill to "relief" holes in the plate of the thermostat. If the one that causes overheating opened in the pan of water, just drill the holes in the plate. Two holes (maybe 1/16") allow some water to flow past the plate and seem to heat the spring more evenly (?)... Not sure why it works but I have used this trick with old dodges and BMWs and it has not failed me yet.

Good luck.

[Mmusicman]

Put in a 160 safety stat and drove it for a couple months that way until I noticed it started barely getting up to 160 temp and was running more like 140 most of the time. Pulled the t-stat and it was stuck open as designed so I threw in a 180 normal t-stat. Now it makes this water hammer gurgling noise after about 5-10 minutes of running has blown off the upper radiator hose if I try to drive it, kind of like if it's a stuck closed thermostat.

Alright, lets look at this "logically":

By your comments... the 160 thermostat ran fine (in fact is ran almost too cold). This would seem to indicate to me that there are NO issues with your cooling system whatsoever! The radiator, pump, engine block, heads, even thermostat seem to have all performed correctly and perfectly.

The 180 t-stat gurgles (and overheats?) like it is stuck... well then perhaps it is. But you go on to say you've tried others and same problem? Yet only 160 works fine? This really makes little to no sense.

1) As suggested, try putting the thermostats in boiling water to verify they work! If it's sticking shut, then its obviously defective!

2) Are you sure you have the correct thermostat? Big difference between the "short" thermostat with single function, and the "long" thermostat with the "bypass valve (see photo below). Does your manifold have the built-in return system, or is it the older style? Both type thermostats may physically fit, but the wrong one with the bypass valve won't be able to physically open in an older style manifold that doesn't have the return system.



3) Drill the 1/8" bypass holes in the thermostat. This will help relieve air pockets, as well as provide smoother transition from cold to hot, and visa-versa. I discovered this trick before I ever heard of anyone else doing this. I noticed the system would become shocked and gush out my pressure cap when the t-stat would open.. even though the cooling system was in perfect order. The relief holes solved my problem.



Hammering sound usually means you are overheating... which you should have seen on the gauge. Be extremely cautious when dealing with this.. always let vehicle cool down before proceeding.

[Astro Pop]

In my history of working on vehicles the hammering is the sound of overheating from a closed t-stat (boiling in the block). That said...
Always start diagnosis from the basics. What is the airflow across the radiator? I like to start the vehicle from cold with the radiator cap off and watch it until it gets up to operating temp while watching the radiator fluid and everything else in the engine compartment. When does the fan kick in, any strange noises, leaks, etc. If it starts shooting coolant up like a geyser relatively soon after starting you've got a blockage. Safety tip ....don't stand directly over the open radiator while doing this it burns, trust me. It's harder with the cooling systems currently used. I used to see the flow across the top of the tank. That helps to see when the t-stat opens. What is the temp at the time the t-stat opens if it opens? You get the idea, the basics will lead you to the actual source rather than guessing what "might be".
What are you using to read the temp? Please don't tell me the factory instrument gage. Like I said basics...question everything and analyze every step from the very beginning. It sounds like you're already pretty deep into this so I hope some of this helps. My old IROC overheated terrible until I replaced a 4" plastic airdam attached to the bottom radiator support to restore proper airflow. I didn't realize a curb had removed it. Expensive lesson for me also.....airflow and simple sh**.

[RECox286]

Water hammer is a sure sign that the T-stat is not opening, and the water in the jacket is boiling. Stick with no frills Stant 180*

and you should be OK. Your anti-freeze: red or green ?

Uncle Bob

[4x4 VanMan]

It acts like a stuck thermostat, I can put my fill funnel on the radiator and watch it run with out a cap on. The level stays put for about 5 minutes, then very tiny bubbles that increase in size followed by increasing coolant level until it pukes it out all over the place. The bypass thermostat is really making sense now after looking at my old manifold.
thanks for all the help, I will let you know how it works out tomorrow.

[Astro Pop]

That sound like plain old overheating. A stuck thermostat acts like ole faithful. It really rockets out of the fill spout, not bubbles. Just for kicks try warming the engine up and put a garden hose on the radiator to cool it down and see what happens. Maybe the radiator is just flowing poorly. I'm assuming the rest of the system is pristine. No rust or blockages.

[4x4 VanMan]

The van was a cool running dependable daily driver until I changed my top end. I went from iron eagle heads, performer rpm manifold and vortec exhaust manifolds and then upgraded to 200cc/64cc aluminum heads, Air Gap clone manifold, and shorty headers.
I was running a 195 normal thermostat with the iron heads.
Put that same 195 in my new set up and she starts the puking out the coolant in under ten minutes deal. Bought the fail safe thermostat and was driving it until I realized it was running too cool.
When I temp gun the engine with a 180 normal t stat the block stays about 180 while the back of the heads start to go over 240 and then she starts puking and gushing.
This is the manifold I'm using and the old rpm manifold. Notice the big height difference between the two thermostat housings ?

[Astro Pop]

Some 350s were reverse flow blocks. water went to the heads first to prevent just this problem. What do you have? Did you talk to the company you bought all this stuff from? some combinations just don't work well together.

[Mmusicman]

Proper manifold and head gaskets? Some block off flow passages...

[4x4 VanMan]

Problem solved ! Changed to the newer style thermostat and no change, then I get to thinking about the heater core hoses. So I pinched the heater hose off while it was running and the banging noise slowly begins to go away and the back of the passenger head no longer gets up to 240 and runs like it should now. The huge heater fitting was killing my flow of coolant to the rear cylinders. All that work for a 5$ fitting, at least I didn't rip my engine apart again and it has some better parts holding her together now. I thought I was using a fitting with a restrictor but the smallest internal diameter is about 1/2 inch. think I need a fitting with an orfice about the size of a .22 bullet. Or I could hook the heater hoses to the back manifold cooling ports and have some cross over cooling action.
Anyway
Thanks to everyone for their input and help.

[nwmod39]

Any chance you are using an aluminum radiator?

We have overheat some in circle track racing and had the radiator swell up, closing off airflow through the fins.

[4x4 VanMan]

It's my second new stock size radiator. Time to spend some $$ and upgrade my cooling system. Going to start looking for a larger oem style radiator that I can squeeze in and going to upgrade to a high flow water pump for some extra protection. I like OEM parts where you can use them because their readily available. Probably move up to electric cooling fans also.

[4x4 VanMan]

Instead of looking for the old style restricted intake fittings I decided to try this route.
This style heater valve restrictor has about a 5/16 orfice to slow the coolant flow to the heater core and keep up the water pump pressure. I utilized ones of my rear intake cooling ports and ran one of the heater hoses there instead of in front and the return hose into the radiator. runs even better this way.

[Mmusicman]

..Put in a 160 safety stat and drove it for a couple months that way until I noticed it started barely getting up to 160 temp and was running more like 140 most of the time..

Bad "heater fitting" doesn't explain why it ran so cool with a 160 stat, but overheated with a 180...

[4x4 VanMan]

The 160 thermostat was a stuck open failsafe, which is more like having no thermostat or a 5/8 racing restrictor washer. In addition to the added flow, I think any steam that was getting up to the thermostat housing would more easily exit instead of backing up behind the thermostat and cause a boil over.
I think a weak flowing water pump may have something to do with all this also, but she's good to drive again until my water pump shows up.

Update:
Since the van is running so much better with passenger head running so much cooler, I gave the driver head the same improved circulation treatment. So both rear manifold cooling ports are now tee'd together then routed through the heater core inlet and out to the 5/8 return on the radiator.
It runs so much better than it ever has, my AFR readings have leaned out a bit now that's hitting better on all 8 cylinders, no more rough idle when warm and never gets above 200 degrees.
Much like this expensive set up but for a fraction of the price. Not much difference if the coolant exits the top of the thermostat housing like this or the top of the radiator.