Thermostat problems

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bigdawg

Master Mechanic
Oct 9, 2011
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without a thermostat the car idles at 140 which i know is too low so i put a thermostat thats 195 degrees and it will raise to like 220 then drop back down to 195 then raise back up whats the problem? and i returned the first thermostat and got another same problem. am i doing something wrong? i dont want to play around with overheating engine
 
Yea the 195 I have in my jeep usually makes my engine run at about 205-210. The 195 I have in my lt1 typically is at 210 or so. The 160 in my sbc 355 runs at 160 and never gets much warmer. Weird aint it? :mrgreen:
 
bigdawg said:
put a 160 thermostat and it stay at 160 dont know what the deal is with the 195


that's because the spec given, for example 160, is when the thermostat begins to open. I'm betting that at 160, with the thermostat begining to open, it's enough to maintain that temp given the cooling capabilities of the radiater and fan. There are other factors as well, like outside temp and engine load. I would try the 160 for awhile and see how it goes.
The 195 thermostat, I believe, is designed to not fully open until it reaches about 210. So, you may be in the normal range with that. Unless you have some issue in the system elsewhere. What type of fan are you using? Clutch? Flex fan? Is your waterpump functioning properly? What sort of coolant are you using? Mix ratio? Is it new? Old? Is your radiator cap maintaining correct pressure?
 
totally makes sense what your saying about the cooling efficiency of my system, completely over looked the idea of that at 160 its much easier to keep it there and at 200 degrees the thermostat has to completely open to cool it down

right now im using a clutch fan from a 84 firebird that had 305 from the junkyard, aluminum radiator from autozone for like a hundred bucks lol for a f body and the water pump is new basic water pump and yea i got a shroud top and bottom
 
the radiator cap i dont know what pressure it is. i bought it new from autozone but it was like 3 years ago

right now im running hundred percent water 8)

i think im either just gonna get a 180 and see what happens or use the 195 in the winter since it would be way easier for it to stay there and i want good heat
 
The cooling system really doesn't care what degree thermostat it has, it will keep it cool (or not) regardless down to that temperature.

Now if the cooling system is undersized or having other issues that is keeping it from being able to cool the engine properly all that a lower temp thermostat is going to help with is delaying the engine overheating by a little longer.

For example, say your engine runs at 210*F because the cooling system can't keep it any cooler than that. Let's say it takes 1 minute of run time for the engine to reach 210*F with the 195* thermostat. Now if you put a 160*F thermostat in place, the engine is still going to reach 210*F because the cooling system can't keep up. However since the thermostat opens sooner it lets the coolant get a head start on cooling (so to speak) which means you now go from 1 minute of warm up time to say 5 minutes before you hit 210*F.

You may have already known this and it doesn't really have anything to do with your original post but is something to think about. A lot of people think if the engine is overheating that they should install a colder thermostat but that is only a bandaid for a problem somewhere else in the system.
 
Another thing to consider, the thermostat is in the intake and most of your sending units for the temp gauge are in the head. I've seen 10-15 degree temperature differences between the two.
 
You should always test a thermostat in a pot of boiling water with a candy thermometer. You'd be surprised how off even new stats are. I often reject several before I get one that works correctly. And by correctly I mean it opens AND closes when it should.
 
my sending unit is in the intake right next to the thermostat its a 350 from a suburban that i put in myself heres a video of it running

viewtopic.php?f=25&t=40070

i know how a thermostat works but for some reason i got 2 of them that dont keep it at the 195 its supposed to... without a t stat she stays at like 150 after driving for an hour so its just weird but i have herd more than once that thermostats are junk these days
 
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