Help me solve a cooling issue. Pic's inside.

1985 k20. 350/400

Long story short, I put a new intake on last year. The truck constantly ran at 210 anything over 55/and above MPH. 35/50 MPH I run like 200 deg.
I NEVER had this problem before intake swap. Here's the deal. I went to my local auto parts and ask for a factory thermostat. I was told and given a 195. That was factory he said. I can hear my valves clatter at 210. All this time I been thinking it was my water pump, Reverse flow
or thermostat. So I figure I start with one thing at a time. I pulled the radiator cap off and could hardly see water flow. Even when it was 200+ degrees. I thought this was because my radiator is huge, its out of a 1999 suburban 454 2500. Anyways, I pull the Tstat and BINGO, I have water flow, it even takes forever to heat up now. With this radiator it wont heat up at all while im moving. If im in traffic I can run one fan and it stays at 180 degrees. With 2 fans, it runs to cool.

here it is in traffic with one fan going. NO T-STAT


here it is on the freeway at 70MPH with no fans going. NO T-STAT



Here is my radiator setup.

So what should I do to keep it under 200degrees? should I start with a 180 Tstat? or go lower?
the price of a Tstat are 18+ dollars I dont really want to experiment with to many LMMFAO!

I don't know how you have bypass set up,but if you don't have some sort of bypass provisions,the water doesn't move and the stagnant water doesn't heat the thermostat to open. If you haven't,then research how others have their bypass setup. Something else to try would be drill a 1/4 hole in the thermostat next to the plunger so it still works it just has a bypass at the thermostat.If not enough room drill a couple of smaller holes.

Ricko1966 said:

I don't know how you have bypass set up,but if you don't have some sort of bypass provisions,

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Are you talking about from the intake to waterpump? I have ZERO bypass. Thanks

Nasty-LSX said:

Are you talking about from the intake to waterpump? I have ZERO bypass. Thanks

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I do not know how bypass is setup or what's needed on LS,but it's what I would research,look at your old manifold. Coolant passages,hoses,seen if you can figure out if you accidently/unknowingly eliminated a bypass.

Ricko1966 said:

I do not know how bypass is setup or what's needed on LS,but it's what I would research,look at your old manifold. Coolant passages,hoses,seen if you can figure out if you accidently/unknowingly eliminated a bypass.

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This is not the stepper with LS swap. my bad, This is the k204x4 with a Gen 1 350. original did not have a bypass. old intake is gone. im pretty sure I just need the correct T-stat since it works great without.

Nasty-LSX said:

This is not the stepper with LS swap. my bad, This is the k204x4 with a Gen 1 350. original did not have a bypass. old intake is gone.

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Where were the heater hoses on the old intake vs the new intake. What manifold are you running vs.what manifold did you have. Some sbc intakes have four corner cooling,some do not. That will affect bypass and circulation in the manifold.

Ricko1966 said:

Where were the heater hoses on the old intake vs the new intake. What manifold are you running vs.what manifold did you have. Some sbc intakes have four corner cooling,some do not. That will affect bypass and circulation in the manifold.

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Ill post pics tomorrow

In circle track cars we didn’t use a thermostat.
We would use a piece of sheet metal cut round like the Tstat, with a dime size hole in it…

For my ‘75 350 I used a Stewart Stage One water pump (iron body, higher flow than stock) and a Stewart high flow 195 degree thermostat. Thermostat has about a 1/8” hole in it, with a poppet in the middle that provides a little flow even if the thermostat is closed. My heater hoses come from the fitting on the intake to the heater core, and then return to a fitting on the radiator. Aluminum radiator and factory clutch fan.

Based on an aftermarket mechanical temp gauge, my engine temperature sits a little above 190, and may come up to about 200 when idling after a highway run with the A/C on. My 195 thermostat may be a little cooler than spec, or maybe the gauge is off a little.

What brand of thermostat did you buy, and what is the routing of your heater hoses? It sounds like water is not making it to the radiator and getting cooled.

OK, UPDATE. I remember before I swapped intakes that I did not have my heater hoses hooked up because
my heater core was leaking. Still never ran at or close to 210 degrees. here is what it looks like now.



So I had a edelbrock 180 laying around waiting to install on the 80 Z28. I used it just to see what would happen.



I must have had a bad T-stat or to high 195. With this 180 in traffic or driving 70 at 3000 to 3500 RPM it wont get hot. All in All it was just the T-stat. This was after a freeway run at high RPM. 3/speed with 410 gears. Thanks everyone

75gmck25 said:

What brand of thermostat did you buy, and what is the routing of your heater hoses? It sounds like water is not making it to the radiator and getting cooled.

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One hose goes to the water pump and one hose goes to radiator. There is no bypass. Works great now!

In the past, I had a pinhole leak in my radiator (not leaking any viewable fluid) and had a similar experience. May need to get both your radiator and heater core pressure tested.

Nasty-LSX said:

One hose goes to the water pump and one hose goes to radiator. There is no bypass. Works great now!

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Bypass is drilled in block,but some use more bypass,I don't think vortec blocks are drilled for bypass,so some use heater core as bypass. If your block doesn't have this hole,or it's plugged you have to provide bypass some how. I thought maybe yours was plugged or maybe vortec block.

I had temp problems with my 76 Sub. I had a flex fan on it, with a 3.73 gear n no OD the engine rpms pretty high. the fan would flatten out an temp went up. swapped in a Ford 5 big blade. then I had an oriley 'stat which was no good. under warranty [lucky me] put a different brand 160 in and never moves off the first mark. finally. Rod in hot AZ.