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Old 12-09-2011, 02:46 PM
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SBC runs too cold with 195 tstat

My 350 is running around 150 now that i've put in a 195 thermostat. It was running about 140 with a 180 thermostat. I've bypassed the heater core by going from top of water pump to intake if that makes any difference. My radiator is a huge Anderson model. My hose going to tstat is pretty warm after running. Otherwise, I don't know what the heck is going on that would keep it running so cool. Ideas? I'm about to buy another temp gauge to be sure, but this SW one has been accurate in recent motors, i believe. Thanks
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Old 12-09-2011, 04:21 PM
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cool sbc

check the radiator cap, is 17 to 19 lb.
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Old 12-09-2011, 06:08 PM
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I have an aluminum 3 core radiator in my truck, too big, and my built sbc only run's 160 degrees on an 90 degree day. I block off part of the radiator to make the engine run warmer if I want too. I also have triple checked my temperrature with laser, and different gauges and sending unit's. Here in Ohio I do not drive the truck during the winter. I have been told, some people would love to have their engine run this cool. I run an hi-flow 195 degree thermostat also, with an 16 lb cap, with built in temperature gauge, to double check my Auto Meter gauge.
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Old 12-09-2011, 06:17 PM
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I had this problem in my daily driver '81 c-10. I tried several thermostats with no luck. I finally figured out it was the cheap chrome thermostat housing. I replaced it with an original GM cast iron unit. I think the coolant was getting around the thermostat.
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Old 12-09-2011, 06:18 PM
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checked it, it was 16lb one, so i swapped it with car that works right, and it still wont get over 150 degrees idling for 10 minutes. It's not cold here either, like 60.
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Old 12-09-2011, 06:26 PM
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My thermostat housing is a fancy, not cheap, chrome one with an O ring that made me wonder ... could that be the culprit? I've never had probs with those original ones either. That might be my next try as I'm running out of options and radiator cap seems OK. Thanks
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Old 12-09-2011, 06:34 PM
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Buy a quality thermostat.......many of the cheap ones are very inaccurate. You can test yours by boiling a pot of water ....a 195 should open just before the water boils
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Old 12-09-2011, 06:47 PM
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i would suggest you try another gauge
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Old 12-09-2011, 07:16 PM
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Quote:
Originally Posted by 68HellCo
My 350 is running around 150 now that i've put in a 195 thermostat. It was running about 140 with a 180 thermostat. I've bypassed the heater core by going from top of water pump to intake if that makes any difference. My radiator is a huge Anderson model. My hose going to tstat is pretty warm after running. Otherwise, I don't know what the heck is going on that would keep it running so cool. Ideas? I'm about to buy another temp gauge to be sure, but this SW one has been accurate in recent motors, i believe. Thanks
The choices would be:

1) The gauge or its sender or wiring between if electric is faulty.

2) The thermostat is faulty, opening too soon for the temperature or leaks coolant past itself.

The bypass hose needs to connect at the manifold before the thermostat and into the pump bypass fitting. The purpose of the bypass other than a source of coolant for the cabin heater is allow coolant circulation through out the engine when the thermostat is closed. It prevents the pump from cavitating when there is no flow from the radiator and it prevents super hot spots from forming inside the engine before there is circulation through the radiator. This is mostly a concern around the spark plugs and exhaust valves especially the paired valves on the SBC and other similar designed engines like the Chrysler A and B blocks. All this circuit ever does is cycle returning coolant under pump pressure from the block back to the intake side of the pump. Different years and models have some variation as how this is plumbed; some return to the pump fitting, others into a T fitting on the suction (lower) side hose between the radiator and the pump, others into a fitting on the suction side tank of the cross-flow radiator. All result in the same functionality.

The thermostat restricts flow to maintain a desired temperature. In the case of most cars and small trucks this is done by restricting the return flow to the radiator. Big trucks and heavy construction equipment often do this on the intake side of the pump or both intake and return. The LT1,4 and the newer LS series does both ends with a mixing chamber that can add hot return coolant to the cooler flow from the radiator, the purpose is to eliminate the cold chill on the front two cylinders typical of the older SBC and most all other engines.

The size of the radiator really doesn't matter a lot unless you live in a really cold climate where the small amount of leakage past an otherwise closed thermostat is sufficient to hold down operating temps. This can be a big problem with thermostats that have vent holes in them which are there to assist passing vapor out when the thermostat is closed. But it doesn't take much of hole or several small ones to add considerable warm up time and perhaps pass enough to where the coolant can't warm sufficiently to open the thermostat, especially when confronted with an oversized radiator and the mass of additional cold coolant that such a radiator carries as reserve capacity.

What you should see is the operating temp range about 10-15 degrees above the thermostat's stamped opening temp which means for a 180 a gauge temp of 190-195.

Question, does this truck have an engine oil cooler? If so is there thermostatic bypass on it to prevent cold oil from circulating through the cooler till the engine warms up? In a cold climate an un-regulated oil cooler can be enough cooling to keep the coolant from reaching operating temp in cold weather.

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Old 12-09-2011, 07:18 PM
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thanks, my brain froze and forgot that's next. I boiled the thermostat and it opened at 180 but doesn't appear to shut all the way when run under cold water. I'm going to try known working accurate gauge and will see what it reads.
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Old 12-09-2011, 07:31 PM
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The El Camino has a transmission cooler and a monster aluminum radiator. It doesn't have an oil cooler. So I'm looking at either bad gauge or wiring or unit and maybe bad temperature gauge No. 2 as options. My other car is running a plugged water pump and manifold water inlet. Should I run a bypass hose. I get these temp spikes where the car jumps to like 240 and then dives down to 180. I thought it was a goofy gauge but now it sound like the hot spots you mention, near the temp gauge. thanks
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Old 12-09-2011, 07:56 PM
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Once you're sure the radiator is full, the gauge is accurate and the sender is submerged, you need to actually drive the vehicle- not just let it idle- in order for you to know what temperature it will get up to.
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Old 12-10-2011, 02:17 PM
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Quote:
Originally Posted by 68HellCo
My 350 is running around 150 now that i've put in a 195 thermostat. It was running about 140 with a 180 thermostat. I've bypassed the heater core by going from top of water pump to intake if that makes any difference. My radiator is a huge Anderson model. My hose going to tstat is pretty warm after running. Otherwise, I don't know what the heck is going on that would keep it running so cool. Ideas? I'm about to buy another temp gauge to be sure, but this SW one has been accurate in recent motors, i believe. Thanks
Sounds like your gauge is off. You increased the thermostat rating and the gauge went higher. How big the radiator is as no impact on engine temperature. The thermostat regulates the temp. If it is closed no coolant is going through the radiator to be cooled. Get a thermometer and put it in the radiator to see what the coolant temp is then go from there.
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Old 12-11-2011, 06:47 PM
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My 350 that is running too cold registered a 140 thermometer reading at the radiator after good drive and gauge said 150. My other 350 that runs normal at 180 had a 170 reading at the radiator. This is the second thermostat installed now, a 195 that replaced the previous 180 unit. Could it be the thermostat housing as one of you suggested, allowing cooler water to gush by? Car heated up to nearly 160 on gauge before it started to dip to 130-140 and then settle on 150. Ideas? This is driving me nuts. Thanks.
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Old 12-11-2011, 06:57 PM
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Other details: My oil pan is an 8 quart one, my huge radiator is aluminum and my water pump is some aluminum after-market pretty thing that may be slightly higher output. Dunno for sure on pump.
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