Is my radiator to big


Just my two cents after not reading everything. I can attest that my 350 Olds diesel had the standard at that time 185 degree thermostat. No different than a gasser. Whenever I ordered a car, I always added the heavy duty cooling option. It mainly was a larger radiator and a larger mechanical fan or in the case of electric, you got two fans instead of one. Also on the diesel and sometimes the other cars, in severe winter temps, I would have to add cardboard in front of the radiator in order to get it to operating temps. Especially the diesel. I don’t know what the flow was but in general, a larger radiator was a good option, especially as the car and radiator aged. An extra margin of cooling.

When replacing thermostats, I always did the water pan test first and usually used Stant brand. Now I’ve started just buying OEM for about 3 or 4 times the cost, but seems to be better quality and more reliable. If you are having problems go with a quality thermostat and cover the front in north country winter temps.


Well it is a 1986 Chevy K10 with a SBC 350, take the diagram you posted here and simply have the return hose from the heater core go back to the radiator and you have the circuit for all square body chevys.


I have replaced the fan clutch, and the problem started the very day I replaced the radiator. It is the radiator size, no other way to explain it. When the engine is loaded heavy enough to allow the thermostat to modulate it is fine, when the engine doesn’t make enough heat to keep the stat open then it bounces around.
The heater temp is not the question, the Head temp is what I am referring to, the factory eng temp sensor located in the head near #1 spark plug


It was relevant because the question was can a radiator be too big, and that was my original question. are the systems different, yes, is the bypass the reason it’s a problem not completely, but it is part of the problem. one more thing to note, the heater hose outlet at the manifold from the factory does only have a 3/8" hole, many mechanic have drilled this out to “fix” a poorly performing heater core rather than replacing the core.


The diagram shows the only path back to the rad is through the thermostat at the top hose. That is a SBC diagram.


well I have used Stant, and I have ordered the best I can get in the way of thermostats, I have replaced them 3 times now and tested all of them and they all worked fine. I am now running a 205 deg and if I have some load the truck runs right at 205, if I am unloaded it bounces between 155 and 205 up and down up and down. If it is raining and cool, it spends a lot more time at 155. I would bet anyone $100 that if I put an original OEM Brass radiator in with a 195 deg stat it would run right on temp just as designed, just as it did before I switched radiators, but the 4 pass aluminum that I have in there now is probably 3 to 4 times the cooling capacity of the brass 2 pass that was OEM.


Did you look at the guys photograph? Heater return on these trucks is to the Radiator Tank.
I agree that your diagram is one possibility, and my pump does have a plug in that location, but that is not how the factory had it set up, and I would have to cap off the radiator connection if I returned my heater to the pump and that isn’t an easy thing to do.


It’s not relevant to the Camry in question because they are completely different arrangements. The bypass in the Camry is a tiny hole in the thermostat flange, not a 3/8" hose.

I’ve built and restored many BBC configurations for street rods and hot rods and put in huge radiators that cost boucoup bucks in the beginning thinking it was needed to keep the temps in check. I later found that a stock rad with the proper shroud (i.e. flow control and distance from fan) was perfectly adequate. The big aluminum rads didn’t prevent the engine from getting to temp, which, if overcooling was an issue, would happen. The thermostat did it’s job just fine regardless. Now if you’re talking about something being modified from the original design and stealing more flow from the heat controlled path, that’s entirely different…just my experience YMMV.


One note on thermostats being analog in nature, you are correct they are analog, but what they are not is linear flow, therefore the flow rate does not increase in a consistent manor based on % open of the stat. In the first 10% flow goes from 0 flow to about 50% of Max flow. A liner flow valve such as is used in a steam heating system has to be a plug type valve with a very specially shaped plug in order to achieve those flow characteristics. therefore cycling of the thermostat does occur from too much cooling capacity.