SBC350 - 160F while driving, 200 at traffic light

[kikkegek]

I wanna check something with you guys.

I have a 195F thermostat in my cooling system. but at a traffic light the engine will warm up to 200F and then the electric fan will kick in and cool it down to 185F and shut off.

but as soon as I start driving, both in town and highway, the engine is cooled down to 160F...even on long drives...

how can this be? and isnt 160F far too cool for a small block? I thought it should be at 190-200F?

I checked the thermostat and it opens and closes at about 185-190F.
see this video (sound is crappy, sorry!).

So the thermostat seems fine. but if this doesnt open untill 185F, why does my engine run so cool?

YouTube - Thermostat test 195F

[russgt]

What are you running for a radiator?

[kikkegek]

Originally Posted by russgt

What are you running for a radiator?

I guess the original one that came from factory. three rows thick.

here you can find all the pictures from my car:
http://picasaweb.google.com/jochenz/...6K20Silverado#

[russgt]

It looks like you installed a flex fan, are you still using it? I would suspect that the extra air flow from the flex fan at speed is causing the extra (160 degree) cool down while driving. A clutch fan would disengauge at speed but the flex fan is still pulling. At low engine RPM (while sitting in traffic) you do not have enough coolant flow/air flow to keep the engine from warming up (200-210 degrees) the good new though is that your electric fans are working correctly and can cool down the engine.

[kikkegek]

Originally Posted by russgt

It looks like you installed a flex fan, are you still using it? I would suspect that the extra air flow from the flex fan at speed is causing the extra (160 degree) cool down while driving. A clutch fan would disengauge at speed but the flex fan is still pulling. At low engine RPM (while sitting in traffic) you do not have enough coolant flow/air flow to keep the engine from warming up (200-210 degrees) the good new though is that your electric fans are working correctly and can cool down the engine.

the flexfan was replaced by the electric fan. The flexfan kepot the engine at 150F all the time (too cold)!

now with the electric fan the temp rises to 200-210F at traffic light but while driving the electric fan is off, but the engine still cools down to 160F....and the e-fan is off!

[Psycho71]

You could try blocking a portion of the radiator. That would effectively remove cooling capacity from the radiator. Just don't get too aggressive. I have an Aluminum 3 row in my burb w/a 180*stat, it runs a constant 180-185*. My '71 has an aluminum 2row w/a 180* stat and two electric fans. It runs 180 at idle all day long, and gets up to about 190* on the hwy. I'm thinking the shrouded electric fans actually inhibit airflow at hwy speeds. It'll get a 3row in the future. I know 190 is not bad, and that's why I have yet to change anything. But I too expect one to run really close to the temp range of stat I have in the water neck.

[78 Chevyrado]

How can you tell what the temp is when your going down the road? what are you using to measure temp. The dash gauge is worthless for telling actual temp numbers, and the cap in the radiator can be off by as much as 10-15 degrees difference between the radiator and engine block, especially if the T-stat is closing. The only way to know the engines real temp, is to measure directly from the block, cylinder head, or intake manifold BELOW the T-stat.

When my intake reads 198 in my truck, at the radiator it reads about 182.

If you're engine is truly cooling below 190-195 degrees, the T-stat is what it is, unless you have a bypass somewhere besides the heater hoses.

If you are going by the radiator cap for temps, double check it against a known good thermometer, just in case. If you can get your hands on one, try to come up with an infrared thermometer. They are awesome.

Are you using the air conditioner? depending on how you hooked it up, the AC may make the fans run when it does. My truck runs the coolest at a red light, with the AC on.

[tobiahr]

what spark plugs are you using? using to low of a heat range plug can have the same type of effect although i've never seen something this extreme.

[kikkegek]

Originally Posted by Psycho71

You could try blocking a portion of the radiator. That would effectively remove cooling capacity from the radiator. Just don't get too aggressive. I have an Aluminum 3 row in my burb w/a 180*stat, it runs a constant 180-185*. My '71 has an aluminum 2row w/a 180* stat and two electric fans. It runs 180 at idle all day long, and gets up to about 190* on the hwy. I'm thinking the shrouded electric fans actually inhibit airflow at hwy speeds. It'll get a 3row in the future. I know 190 is not bad, and that's why I have yet to change anything. But I too expect one to run really close to the temp range of stat I have in the water neck.

I keep forgetting to do a test like that, to check of the rad is cooling,although the engine temp is below thermostat temperature.

[kikkegek]

Originally Posted by 78 Chevyrado

How can you tell what the temp is when your going down the road? what are you using to measure temp. The dash gauge is worthless for telling actual temp numbers, and the cap in the radiator can be off by as much as 10-15 degrees difference between the radiator and engine block, especially if the T-stat is closing. The only way to know the engines real temp, is to measure directly from the block, cylinder head, or intake manifold BELOW the T-stat.

When my intake reads 198 in my truck, at the radiator it reads about 182.

If you're engine is truly cooling below 190-195 degrees, the T-stat is what it is, unless you have a bypass somewhere besides the heater hoses.

If you are going by the radiator cap for temps, double check it against a known good thermometer, just in case. If you can get your hands on one, try to come up with an infrared thermometer. They are awesome.

Are you using the air conditioner? depending on how you hooked it up, the AC may make the fans run when it does. My truck runs the coolest at a red light, with the AC on.

I use the dash gauge for temp readings. I know this one is right. The sensor sits in the block on the driver side between the spark plugs.

The temp it shows is correct, because as soon as it hits 200F, my electric fan kicks in. The thermostat of the electric fan kick in at 200F and off at 185F. The temp sensor of the fan sits in the thermostat housing.

I recently checked the thermostat, cooked it and it opens and closes at about 185F. A little early for a 195F thermostat, but close enough.

I do have a little bypass in my system, its the evaporator of my LPG system. But I already investigated that and its supposed to use very little heat as LPG evaporates already at room temperature.

So I am still in the dark why my car cools down to 160F while driving and then heats up to 200F at the traffic light. Seems like it is getting cooling through the radiator, but it shouldn't, because the thermostat should be closed.

[kikkegek]

Originally Posted by tobiahr

what spark plugs are you using? using to low of a heat range plug can have the same type of effect although i've never seen something this extreme.

I have absolutely no clue. I need to check that. But LPG already burns warmer then regular fuel. So I am not looking in this direction.

[RaVeNlI666]

Not to hijack your thread but I am having more or less the same problem with my 79 Blazer. I have an auto meter water temp gauge and it will get up to 200 at a stop light, and even if I am going 25 mph it will drop to 160, if i am going down the freeway it will go as low as 140. Probe is before t-stat on intake. Dual elect fans on a 383 stroker and a rad from an 82 chevy PU. only thing I changed on mine was the intake. went from a dual plane to an air gap......

[kikkegek]

Originally Posted by RaVeNlI666

Not to hijack your thread but I am having more or less the same problem with my 79 Blazer. I have an auto meter water temp gauge and it will get up to 200 at a stop light, and even if I am going 25 mph it will drop to 160, if i am going down the freeway it will go as low as 140. Probe is before t-stat on intake. Dual elect fans on a 383 stroker and a rad from an 82 chevy PU. only thing I changed on mine was the intake. went from a dual plane to an air gap......

dont worry, as long as your having the same problem and hopefully we find some solution here.

I have given up for now.

I had a bypass over the passenger side of the rad, because my evaporator of the LPG system is connected in parallel to my heater core. But I moved the return connection from my heater core to the waterpump.

So now coolant can only flow over the rad if the stat opens. I checked my stat and it opens at about 85C (185F) and its a 195F stat. So I am sure that is not causing the cooling when I start driving.

short analysis. Engine is at traffic light heats up from no cooling to 200-210F and the electric fans kick in. as soon as the tempguage hits 185F the fans turn off...so the gauge is working fine. when I start driving with 200F, the waterpump speeds up, because of the higher rpm, the read cools the water down to below 185F and the stat should close. Now the coolant can only flow through my engine and heater core (wich is OFF) and through my evaporator, but this takes only very little heat I heard. LPG evaporates very easily. so the evaporrrator and the heater core arent delivering any cooling.

So I wonder....what is cooling the engine OR

right now at the traffic light my temp gauge moves between 200 and 185 and during driving it is at the yellow line. for now I have given up...

Maybe the lower parts of the temp gauge isnt accurate and fooling me into a cold engine...

[jjmorrse]

Originally Posted by Psycho71

You could try blocking a portion of the radiator. That would effectively remove cooling capacity from the radiator. Just don't get too aggressive. I have an Aluminum 3 row in my burb w/a 180*stat, it runs a constant 180-185*. My '71 has an aluminum 2row w/a 180* stat and two electric fans. It runs 180 at idle all day long, and gets up to about 190* on the hwy. I'm thinking the shrouded electric fans actually inhibit airflow at hwy speeds. It'll get a 3row in the future. I know 190 is not bad, and that's why I have yet to change anything. But I too expect one to run really close to the temp range of stat I have in the water neck.

You can drill holes in your shroud and install rubber flappers that open at speed. Spal makes some.
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[kikkegek]

Something else I noticed is that the scale on the temperature gauge on the dash is not lineair:

the left side runs from 100 to 210. A difference of 110 degrees.
the right side runs from 210 to 260. A difference of only 50 degrees.

So who know what the number is for the points in between on the left and right side of the 210F?

I know my fan turns on then the gauge is at about what I guess is 200F and the fan turns of when it is at the position in the picture below. It turns off at 185F...

does anybody know the scale of these gauges. What is the value of the points left and right of the 210F?

[68Timber]

I'd guess 155 and 235.