Temp Fluctuation.

Troy

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#1
80's SBC. It didn't have a heater valve so I installed one. It's a 4port. The heater hose to the heater core come off the front pass intake. With the valve installed the Temp gauge fluctuates from normal 180 to almost 260. Idle or driving it doesn't matter. So i ran the heater hose from the intake to the Radiator.Temp gauge seems steady. So I pinched the heater hose off & the fluctuation came back. What would gauge this?
 

kev2

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#2
heater hoses ran form intake to heater core then to radiator.... all was good?

then then installed a heater valve... hoses ran intake to a 4 fitting valve? Am I right? this will be confusing to describe - a picture is a 1000 words here.
Why did you add valve? just curious..

... sounds like you may have 'plumbed it wrong...
normaly the coolant will flow intake then right to the radiator...never enter core.
OR selector moved and coolant flow is intake to CORE then to radiator...
 
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#3
I think that when the intake hose is fastened to the radiator, you are bypassing a bad thermostat. Unless your vehicle is actually supposed to max at 260. Or your gauge/sender is faulty.
 

billr

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#4
On older Chevys, both SB and BB, the heater flow was from intake manifold and back to a nipple on the lower (suction) side of the water pump. I never saw one with a nipple on the radiator for a heater-size hose (5/8" to heater, 3/4" return from heater). I'm pretty confused here about how this is plumbed. However, that fluctuating from normal to very high is always an indication that coolant level is below the temperature sensor, up in a cylinder head. The sensor reads pretty normal from heat conducted to it by the head, then spikes up when some steam hits it. Could be just low coolant level, or more likely an air pocket in this case. Those old beasts were never too fussy about air pockets, but with the unknown plumbing going on here, who knows? I am assuming this car is old enough that coolant flow isn't "reversed", i.e. flow here is from the pump, through the block, up to the heads, then out the intake manifold and t'stat back to the radiator. I also assume the small J-shaped hose between intake manifold and top of water pump is in place.
 
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#5
there was no heater valve because they didnt use them.the coolant flows through the heater core all the time.if it didnt exhibit these symptoms before you installed the valve taking it out should do the trick. hey bill the trucks with the heavy duty cooling system had the heater return into the rad.
 

Troy

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#6
Sorry about that. I will try to be more clear. Al daniels you are correct! From the factory the 5/8 hose comes of the intake & goes to the Heater core inlet. 3/4 comes out of the heater core to the radiator. I will try to get a pic of the valve. But it's the same valve like on a 97 chevy truck Delco 15-5533. Pretty sure I plumed it correct. When vacuum is applied it just bypasses the heater core & it just reverts the coolant straight back to the radiator like factory. Reason for installing the valve was to see if heat was blending in with the ac. I should also not When it was hooked up like factory I just pinched the 5/8 hose off that goes to the heater core inlet. The temp gauge started to rise so I thought it had to do with blocking the flow of coolant so I wasn't able to actually check it. I then installed the valve & the temp gauge did the same thing. Hmm, that weird. Since I spliced into the heater hoses to put the valve in I didn't have any hose to connect it back like factory so as & temporary fix I kinda had to force the 5/8 hose from the intake to the 3/4 fitting on the Radiator which is just bypasses the heater core. I should also mention I did try to burp it when I had the valve installed but the temp gauge still fluctuated.
So basically stopping the flow or slightly restricting it from the curves the valve causes, causes the temp gauge to fluctuate which doesn't make sense to me.
 

kev2

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#7
Sounds like you were having a cooling problem BRFORE you installed the valve... maybe regroup-
see if OEM configuration is working correct.
Then using a garden hose its summer time 8) you will a have a cool engine to work around no hot coolant to piss you off... moving parts etc...

does the water flow thru the heater core? both ways?
make note of flow - restrictor maybe?
Next does water flow thru valve when in bypass - same rate?
finally select heater - water flow thru valve same?


PS beer is mandatory - when using a garden hose...
 

kev2

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#9
AC better be putting out less than 40deg air for all this F'in work :)
 

Troy

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#10
I took out the heater valve & hooked it back up like Factory. 5/8 hose from the intake into the inlet of heater core. 3/4 hose out of the heater core to the radiator. Flow thru heater core seems ok. Temp gauge still will Fluctuates. It will do it Idle or when Driving doesn't matter. After I hooked it back up like original I took it for a test. The gauge was showing fine at 180 for a few miles, then all the sudden it might go up to like 210-240. Then it would go down to 180 again for a few miles. After a few miles back up it would go. After it cooled off from driving it earlier I went out & started it & let it idle. The temp was at 180 for a few minutes. Then the temp went up to like 220 then it would go back down. I have a 180 stat.
 
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#11
my next question would be,is it really heating up or is the gauge reading wrong.for all the price of a sending unit i think i would just replace it and see. my old chevy would go up to 230 or so but only if it was really hot out and i was working it hard.
 

billr

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#12
Don't forget the wire to the temp sensor, if that connection is loose I think the gauge will go to "full hot" when open-circuit. It may just be an intermittent connection there!
 

Troy

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#13
Billr,
I checked the connection already & it's tight. When you ground the Temp sensor wire to like the frame the gauge pegs, which is what it's supposed to do. Checked the Volts on the wire going to sender & it's 12v.
 
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#14
Troy...have you tried wackin' the dash to see if the temp gauge changes?

Would I be correct in assuming this unknown vehicle has a belt driven radiator fan, probably with a fan clutch?

Could you simply have a binding t-stat, that works properly sometimes?
 

Troy

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#15
Danica,
I will try hitting the dash when the temps go up. You are correct, that its belts driven with the fan clutch. I don't know about the stat, I guess it could be binding for some reason.