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Old 10-23-2017, 12:18 PM   #1
6768chevylover
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blazer runs to cool

I have a 71 blazer with a 350 that runs to cool in 60degree or less temperatures. It will heat up of course if I was to sit in one spot with no fan on. Once I start to drive the temp goes below 150 and then there goes my heat in the blazer. I was looking at underdriven pulleys to slow my water pump down. Right now my water pump pulley is about a 7" and my crank pulley is 6.75" which is underdriven but was looking into a smaller crank pulley of about 5.5". Would this slow the water pump down to heat up the water in the block more?
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Old 10-23-2017, 12:26 PM   #2
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Re: blazer runs to cool

Also went from a 160 stat to a 195 to 180 which is in it right now. 160 and 195 didn't work either..
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Old 10-23-2017, 12:41 PM   #3
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Re: blazer runs to cool

Easier to restrict the air flow thru your rad.
Use a winter front or a chunk of cardboard to block off part of the rad.
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Old 10-23-2017, 03:03 PM   #4
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Re: blazer runs to cool

X2 with the card board.....it takes my truck about 30 minutes to get to temp cruising in cold weather. haha
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Old 10-23-2017, 10:01 PM   #5
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Re: blazer runs to cool

Do you currently have a stock fan? If so, clutch or solid drive? Even if clutch, clutch might be seized up.

Possible the 195 Tstat was defective. QC isn't what it used to be.

Is it possible your heater core is mostly plugged? Or the heater box is full of grass, mouse nests, etc.?

The cardboard idea is cheap and easy to try.
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Old 10-24-2017, 08:29 AM   #6
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Re: blazer runs to cool

heater core is new and the heater box is clean due to just removing it and cleaning it about 3 weeks ago. when it was warmer out..
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Old 10-24-2017, 09:01 AM   #7
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Re: blazer runs to cool

How cold does it get where you live? In my area it sometimes gets down to the 20's and I've never had a problem with my vehicles getting to operating temp or the heater not working.

I lived in Idaho for a few years and some people used the cardboard to speed up the engine warming but it was never for prolonged use. You might need to check other possibilities if it's something that just happened or if the engine never warms up to temp in long drives.
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Last edited by 68gmsee; 10-24-2017 at 09:40 AM.
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Old 10-24-2017, 09:50 AM   #8
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Re: blazer runs to cool

the coldest its ever been here is around 5. Normally around teens to 30s in the winter. I just recently installed an auto meter water temp gauge. always had the stock gauge but wanted to know exact temp. Its pretty close to accurate. my gauge reads 170, 175 when I drive in 60 degree weather or hotter. When the temps drop here it runs about 130, 135. Based on the gauge. the heater feels nuke warm when its colder out. It will heat up when i'm at idle sitting but lowers when driving. I have to electric fans on the radiator and the stock fan shroud. My theory is to upgrade the cylinder heads to vortecs and boost the compression to make it run hotter. Right now I have the 882 heads on it.. Hate low horsepower. Ha ha ha..
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Old 10-24-2017, 10:16 AM   #9
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Re: blazer runs to cool

Where did you install the sending unit for the Autometer gauge?
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Old 10-24-2017, 10:16 AM   #10
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Re: blazer runs to cool

Two electric fans!
Shut one off!
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Old 10-24-2017, 11:19 AM   #11
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Re: blazer runs to cool

I don't even use the fans in cold temps. I mounted it in the cylinder head in the stock location.
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Old 10-24-2017, 01:21 PM   #12
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Re: blazer runs to cool

You need to check all your temps on your motor with a heat gun!
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Old 10-24-2017, 01:51 PM   #13
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Re: blazer runs to cool

I did what Geezer and TJ said when i had my 69c20. (big 4 core rad)cardboard on half of the rad, only way the heater would work.
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Old 10-24-2017, 03:00 PM   #14
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Re: blazer runs to cool

How are your heater hoses routed?

I’ve had trouble also with cheap chrome thermostat housing pitting. Water would bypass around thermostat.
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Old 10-24-2017, 04:41 PM   #15
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Re: blazer runs to cool

its a non a/c body so my intake hose is going to the bottom of the heater core and the radiator goes to the top. Your scaring me now Geezer.. Don't make me find issues with this engine. I already have another one with my c10 truck engine.
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Old 10-24-2017, 05:27 PM   #16
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Re: blazer runs to cool

Both of my heater hoses go to the engine. One to the intake and one to the water pump. My truck has warm heater. Engine temps stay around 190 at the intake manifold.
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Old 10-24-2017, 06:04 PM   #17
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Re: blazer runs to cool

I think this is how it goes, if it is an auto trans then upper hose should go to radiator. If manual it should go to the water pump.

You might just have to put in a BBC to make some heat.
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Old 10-24-2017, 08:31 PM   #18
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Re: blazer runs to cool

Are you by chance using one of these thermostats? https://shop.advanceautoparts.com/p/...E&gclsrc=aw.ds They don't close down as far as the regular kind do. I confirmed it myself in the kitchen sink. Seems they are designed that way due to being a "performance" item. My motor never wanted to reach 180 with one of those unless it was plenty warm outside.
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Old 10-25-2017, 10:28 AM   #19
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Re: blazer runs to cool

[QUOTE=6768chevylover;8067619]its a non a/c body so my intake hose is going to the bottom of the heater core and the radiator goes to the top..../QUOTE]

Here's a thread on the same subject: http://67-72chevytrucks.com/vboard/s...d.php?t=559186
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Old 10-25-2017, 11:16 AM   #20
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Re: blazer runs to cool

Forgot to add above that you might want to reroute the heater hoses to the engine as mentioned above (intake and water pump). Plug the connection at the radiator with a small section of heater hose and a plug and reroute the heater hose to the water pump.

As the temperature in the area warms you can always reroute to the radiator and plug the water pump opening.
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Old 10-25-2017, 02:41 PM   #21
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Re: blazer runs to cool

AcampoDave, I have that exact thermostat in my Blazer which I'm having the issue and in my c10 which puts out plenty of heat. The only difference is the hoses on the Blazer are different location then the c10. The c10 has the hoses completely on the engine and the Blazer intake and radiator. Maybe ill have to do the swap and put it on the engine.. Makes sense since the engine is always the hottest in the engine bay..
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Old 10-25-2017, 07:33 PM   #22
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Re: blazer runs to cool

Quote:
Originally Posted by 6768chevylover View Post
AcampoDave, I have that exact thermostat in my Blazer which I'm having the issue and in my c10 which puts out plenty of heat. The only difference is the hoses on the Blazer are different location then the c10. The c10 has the hoses completely on the engine and the Blazer intake and radiator. Maybe ill have to do the swap and put it on the engine.. Makes sense since the engine is always the hottest in the engine bay..
Ok , but swapping hoses isn't likely to make your motor reach 180. I was running 150-160, then installed another Mr. Gasket 180 thermostat figuring the first one to be defective...still the same. I then proceeded to throw said thermostat in the garbage, installed an O'Reilly's house brand and....problem solved. 180 even on cold days. Later, I did Google "Mr. Gasket thermostat runs cold" and it seems the issue is rather common in vehicles with a big radiator. (Which I have)
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Old 10-26-2017, 09:05 AM   #23
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Re: blazer runs to cool

You don't happen to know the part number for the thermostat do ya? Oreillys shows three of them for my application. I would like to solve my issue too.
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Old 10-26-2017, 10:21 AM   #24
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Re: blazer runs to cool

3??? Sorry but I don't have a number. Maybe try Rockauto and see if it comes up with 3 also.
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Old 10-26-2017, 11:05 AM   #25
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Re: blazer runs to cool

Dave you are very close.. hahaha
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