Chevy engine temps


#1

I have a '79 chevy Monte Carlo and it just got its 3rd motor(this is a new one). I have a 180 thermostat in it now and have notice that the temp is between 190-210 on highway and then its 215-230 in town. Everything is new.(radiator, hoses, thermostat, thermostat housing, heater core, heads). I am running a flex fan so there is no clutch. I am assuming that the thermostat is bad and I should put in a new one but should I maybe go to a 160? I live in ND and this is a fairly build up motor.( its a 350 bored .030 over with .125 dome pistons and a comp cams xe262H with a holley 80555C carb and summit brand 67cc cast iron heads with roller rockers and with headers and a tru dual exhaust)


#2

I would think 180 would be a good temp to have…especially in those ND winters. With a Hi-po motor, I’d think about a bigger radiator and an electric fan.


#3

I am not planning on driving it in the winter unless as a last resort if my '83 t-10 dies but that is getting a new motor next year. do you think that maybe the thermostat is sticking and causing it to run hot in my eyes or is 230 degrees safe with a cast iron block and cylinder heads?


#4

Just an update. I already have a 3row core radiator with a 18" flex fan. I was checking other specs and thought that these may help. My pulley sizes are currently a 7 or 8" crank pulley with a 6.25 water pump pulley. My sending unit for the temp gauge is in the head and is a mechanical gauge.


#5
You may want to make sure the gauge reading out the temperatures is accurate.  

The difference in temperatures indicates three likely issues:

Thermostat.
Fan not functioning properly
Blocked radiator or hose etc.
A small head gasket issue.

I would not use a cooler thermostat. Assuming all your observations are correct that will not help at all and will result in your engine running cooler than it was designed for (lower mileage and other problems) Thermostats are designed to be open or closed nothing in-between So there is no difference in the cooling capabilities between two properly functioning thermostats when they are both over their designed temperature.


#6

180 is the just start to open temperature, the fully open temperature could be like 210. I always test new thermostats by heating it up in a pot of water on the stove with a thermometer in the water. I take not of its just starting to open and its fully open temperature. I have found all the premium thermostat have a much larger proportional band then the cheap ones. Therefore the premium ones will control a steadier temperature but allow engine to run hotter. On the other hand the cheap ones may run more at the rated temperature but cause temperature fluctuation (hunting) that you will probably notice on the gauge. Just curious of the brand/type thermastat.


#7

I bought a stant powerstat. however I had it sitting for about a year before I got it put in. Also I wanted to ask if maybe I should move the fan closer to the radiator? Currently I have a 2" spacer on and I can get a 3" fairly easily. or should I put in a 10" pusher fan on too? I believe that If I change the waterpump pulley to the smaller one (5.5 vs. 6.25) that may help a small bit. The temp sensor is in the head on the passenger side.(just want to state all my gauges are mechanical not electrical{I hate electrical})


#8

“Is it the thermostat?” Well, find out, positively. Take the thermostat out, run the car around the block 4 times, and note the engine temperature. If the engine temperature is the same as before, it’s NOT the fault of the thermostat. +++ Verify the temperature gage…use another, such as, a handheld temperature reader (infra-red). The temperature sender and/or the dash temperature gage could be wrong. There are problem indications, and then, there are indication problems. Test and inspect to tell the difference. ++ The radiator is new; but, was the engine BLOCK coolant passages flushed and cleaned? If not, the rust and minerals that were in the engine block could now be in the radiator. + When refilling with water, use DISTILLED water. It has no minerals.


#9

Ok. So here is the low down… This block was cooked out and I spent an additional 6hours with dawn and hot water scrubbing all oil passages and running the brushes through the coolant passages. The heads and radiator are new. everything is new in the motor except for the crank(which was machined and cleaned the same way as the block), and the rods are stock from naparts.com with arp bolts installed. I have done the drive around but with the extra air moving through the radiator it does get high.(I have not ran it about 230 wich is where it has peaked so far) I didn’t have any problems with break in(2500rpms for 25minutes)with it running any hotter then 190-200 and thats sitting in a drive way in front of a garage with no extra air moving. I am just baffled here. I haven’t ran into this before as I deal more with tuning and other mechanicals but I am expanding my knowledge to continue my business.


#10

Sorry forgot to mention this is a realatively fresh motor with approximatly 160-200 miles on it.


#11

Do you have a fan shroud? If not you need to install one.


#12

I have the factory fan shroud that is complete on it. I have eliminated most easy fixes.


#13

Is the temp gauge an add-on? Does the sending unit match the gauge?
Just wondering if the engine was running cooler than the gauge shows.
If the sending unit is not matching and has a slightly lower resistance in it then the gauge will read higher than normal even though the engine is not running hot.


#14

the sending unit is mechanical not electrical. so it is matched to the unit. it registed fine during break-in but after putting some miles on and driving it instead of putsing around and giving it some realworld driving it gets hot in stop and go driving


#15

Considering it ran normal during break in and is now running hotter, then I’d ask if the timing is still spot on. Sometimes, the dist hold down isn’t tight and it rotates slightly changing your timing. BTW- what is your target setting for timing?

Next, I’d check for a lean condition. Have you intentionally changed your carb settings (some ppl run slightly lean to avoid washdown during break-in)? Is it running too lean now?

I’m less inclined to go this direction since it ran properly during break-in but I’m curious about the flex fan. I run those too but have had some issues with the OEM shroud. First, the diameter of the fan should match the OEM fan size to insure good flow. The fan placement should be 2/3 inside the shroud (front-back alignment) and a long versus short pump, change in spacer or change in pulleys can affect that alignment. Also, the cheaper fans tend to flex at lower speeds and become weak faster. Is it a quality fan? Plastic or metal?


#16

Just wondering what type of a radiator did you put in? a stock replacement or an aluminum after-market? I put a two core aluminum one in my car (1970 Chevelle w/ 350) and now stop and go driving in the summer is almost impossable here in south Houston, TX. It works extreamly well if I’m moving, and is fine in our cooler winter months as well.


#17

Also- What is your idle set at? By increasing my idle just a bit it really helped the engine temperature in my stop and go driving situations.


#18

timing set @ 36 degrees @ 2200 which is the max for the cam and thats with advance. Idle set @ aprox 800. fan is summit brand 18" metal. the radiator is a 3row factory copper style. This dist hasn’t moved and the carb settings are factory set from holley on model #80555c


#19

Oh and I also for got to state I have a bit more back pressure than warrented using the summit brand mufflers(and they state that there is no way that the mufflers cause too much back pressure for this motor) will be up grading those to flowtech terminator mufflers on saturday.


#20

I would also like to state that I get 15mpg on highway @75mph with the motor @2800rpms. I don’t think thats so bad If I slowed down It would probably be better.