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Old 12-04-2017, 02:23 PM   #1
hillbillyrider
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truck wont warm up

94 2wd with 4.3. I have only had it a couple weeks. It will not warm up enough to get good heat. Replaced the t-stat and still won't. Put a half of pizza box in front of the radiator and it still won't. It barely gets off the 100* mark and i am tired of freezing. With the cap off I can give it some gas and watch the coolant level go down. Top rad hose gets hot, bottom little warm. Heater hose in rear gets hot, front little warm. I don't know the history other than the engine was supposedly changed out. But the one they put in is supposedly a little older model. In the pic below it had been idling for 45 minutes. It never get warmer than that.

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Old 12-04-2017, 03:06 PM   #2
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Re: truck wont warm up

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94 2wd with 4.3. I have only had it a couple weeks. It will not warm up enough to get good heat. Replaced the t-stat and still won't. Put a half of pizza box in front of the radiator and it still won't. It barely gets off the 100* mark and i am tired of freezing. With the cap off I can give it some gas and watch the coolant level go down. Top rad hose gets hot, bottom little warm. Heater hose in rear gets hot, front little warm. I don't know the history other than the engine was supposedly changed out. But the one they put in is supposedly a little older model. In the pic below it had been idling for 45 minutes. It never get warmer than that.

I wonder if they reveresed the lines at the heater core when they swapped out motors?
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Old 12-04-2017, 04:18 PM   #3
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Re: truck wont warm up

Check to see if line or heater core is plugged. You can take both lines off, and put some air to the return line, if anything there it will blow it out.
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Old 12-04-2017, 05:00 PM   #4
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Re: truck wont warm up

Could be a bad thermostat, new parts are not necessarily good. More and more new parts are junk! You could put it in some water on a stove and see when it opens.

If it is not the t-stat I would suspect that water is still circulating somehow through the radiator. Make sure the t-stat fits the housing and sales off the water.

Make sure they didn't hook up the heater lines so that it bypasses the t-stat and allows water to circulate.
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Old 12-04-2017, 06:17 PM   #5
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Re: truck wont warm up

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Could be a bad thermostat, new parts are not necessarily good. More and more new parts are junk! You could put it in some water on a stove and see when it opens.

If it is not the t-stat I would suspect that water is still circulating somehow through the radiator. Make sure the t-stat fits the housing and sales off the water.

Make sure they didn't hook up the heater lines so that it bypasses the t-stat and allows water to circulate.

Agree. I bought one a few weeks ago, got home, got the old one out, and realized they gave me the wrong one. Could be defective, or could have been in the wrong box.
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Old 12-04-2017, 08:28 PM   #6
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Re: truck wont warm up

Why would getting the heater hoses mixed up cause the truck to not warm up? Also, the hoses are not bypassed. They are both hooked up. The rear hose is hooked to the right nozzle of the core. The front is hooked to the left. As for the t-stat, the p o changed it before i got it. So it has been changed twice and it still will not warm up to even close to operating temp.
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Old 12-05-2017, 09:51 AM   #7
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Re: truck wont warm up

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Why would getting the heater hoses mixed up cause the truck to not warm up?
Thermostat restricts the water flow through the radiator so it can warm up. If someone had somehow plumbed the hoses so that water was always flowing and not be stopped by the thermostat it might never get warm as you described. And this could be caused by an improper fitting thermostat too.

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They are both hooked up. The rear hose is hooked to the right nozzle of the core. The front is hooked to the left.
If you are saying the heater hoses are hooked to the radiator that might be your problem. A photo of how they are hooked up that might help.
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Old 12-05-2017, 10:38 AM   #8
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Re: truck wont warm up

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Thermostat restricts the water flow through the radiator so it can warm up. If someone had somehow plumbed the hoses so that water was always flowing and not be stopped by the thermostat it might never get warm as you described. And this could be caused by an improper fitting thermostat too.



If you are saying the heater hoses are hooked to the radiator that might be your problem. A photo of how they are hooked up that might help.
i know all about what t-stats do and how everything works. been turning wrenches for many years. it is the RIGHT thermostat. the heater hoses are hooked to the heater core, not the radiator. there is not even a place on a radiator to hook heater hoses to. also, if the coolant was constantly flowing, shouldnt both radiator hoses be about the same temp since the coolant comes in at the top and out the bottom? the top hose is hot and the bottom is barely warm. I think i may do a complete flush and see if that cures it.

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Old 12-05-2017, 11:49 AM   #9
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Re: truck wont warm up

How big is the radiator? Possibly overcooling? Or maybe rad is plugged enough to slow coolant but not enough to overheat?
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Old 12-05-2017, 11:50 AM   #10
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Re: truck wont warm up

Could be your heater core hoses are deadheaded.
On my 98 one goes from the intake to the core and the return hose goes to the water pump.
That's way it's normally set up.
How is yours set up?
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Old 12-05-2017, 11:54 AM   #11
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Re: truck wont warm up

Sorry, just tried to help, good luck.
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Old 12-05-2017, 11:59 AM   #12
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Re: truck wont warm up

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Sorry, just tried to help, good luck.
No problem. appreciate the help.
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Old 12-05-2017, 12:01 PM   #13
hillbillyrider
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Re: truck wont warm up

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Could be your heater core hoses are deadheaded.
On my 98 one goes from the intake to the core and the return hose goes to the water pump.
That's way it's normally set up.
How is yours set up?
the heater hose from the water pump goes to the left hookup on the heater core. the heater hose that runs to the rear of the intake is hooked to the right
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Old 12-05-2017, 12:04 PM   #14
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Re: truck wont warm up

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How big is the radiator? Possibly overcooling? Or maybe rad is plugged enough to slow coolant but not enough to overheat?
the rad looks normal. even if the rad was partially plugged why wont it get up to operating temp. i am sure there are no problems with the heat working if i can just get the engine to get hotter. it wont get above about 110*
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Old 12-05-2017, 12:20 PM   #15
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Re: truck wont warm up





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Old 12-05-2017, 12:21 PM   #16
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Re: truck wont warm up

sorry for the huge pics
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Old 12-05-2017, 04:33 PM   #17
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Re: truck wont warm up

I’d compare with a small block, should routed the same. But if top hose gets hot but bottom don’t, I’d check gauge sensor, 110 isn’t that hot to the touch.
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Old 12-05-2017, 05:31 PM   #18
hillbillyrider
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Re: truck wont warm up

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Id compare with a small block, should routed the same. But if top hose gets hot but bottom dont, Id check gauge sensor, 110 isnt that hot to the touch.
it feels hot but it is not hot enough to where i cant hold on to it. i will check the sensor to be sure it is working correctly.
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Old 12-05-2017, 06:28 PM   #19
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Re: truck wont warm up

Where's the coolant recovery tank?
Is that hose that's clamped to your rad open or is that a plug in it?
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Old 12-05-2017, 06:45 PM   #20
hillbillyrider
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Re: truck wont warm up

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Where's the coolant recovery tank?
Is that hose that's clamped to your rad open or is that a plug in it?
recovery tank sits next to the firewall behind the breather tube. that bigger hose is plugged off. but the overflow is hooked to the recovery tank
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Old 12-05-2017, 08:05 PM   #21
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Re: truck wont warm up

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the heater hose from the water pump goes to the left hookup on the heater core. the heater hose that runs to the rear of the intake is hooked to the right
Looks like you have the hoses set up like a 60's to 70's heater hose set-up, but these systems don't work that way anymore. You've got two "pressure" connections and no return. The connection on top of the water pump should be plugged and routed to the fitting under the radiator cap. That's your return line; from the firewall to the radiator. Have you blasted out your heater core?
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Old 12-05-2017, 08:29 PM   #22
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Re: truck wont warm up

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Looks like you have the hoses set up like a 60's to 70's heater hose set-up, but these systems don't work that way anymore. You've got two "pressure" connections and no return. The connection on top of the water pump should be plugged and routed to the fitting under the radiator cap. That's your return line; from the firewall to the radiator. Have you blasted out your heater core?
it was set up like that when i got it. i haven't done anything to the coolant system yet. would it being set up like that cause the engine to not warm up to operating temp?
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Old 12-05-2017, 09:01 PM   #23
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Re: truck wont warm up

The thing is; do we even know if the engine is going in to closed loop? The gauge is separate from the computer. Some functions are tied in an on/ off manner to the computer like oil and fuel pressure. I think the gauge sender is the same on V6's as well as V8's; on the driver's side cyl. head between plugs one and three. Does the check engine light come on and go out after you start the engine and have it running?
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Old 12-05-2017, 09:17 PM   #24
hillbillyrider
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Re: truck wont warm up

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The thing is; do we even know if the engine is going in to closed loop? The gauge is separate from the computer. Some functions are tied in an on/ off manner to the computer like oil and fuel pressure. I think the gauge sender is the same on V6's as well as V8's; on the driver's side cyl. head between plugs one and three. Does the check engine light come on and go out after you start the engine and have it running?
check engine light works as well as check gauges. no CEL on when running/driving. the temp sensor looks like new. looks to be replaced not long ago. the top radiator hose dont get real hot. just hotter than the bottom. i can stick my finger in the coolant and it is warm but not hot.
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Old 12-05-2017, 11:53 PM   #25
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Re: truck wont warm up

Sounds like the problem is that engine not getting up to operating temp. I'd try old school investigation to find what's causing that problem. first use a thermometer in the radiator to confirm that the guage is showing the actual engine temp. Then I'd bypass the heater core by removing both hoses from it and hooking them to each other with tubing and hose clamps. Run the engine at varying speeds for 15 min. If that doesn't do anything remove the return hose at the radiator, plug the nipple on the radiator with a short piece of tubing and a bolt or something to plug it. Put a water hose with a rag around it in the radiator fill neck and run it some more. If no change make sure the spark plugs are the right ones. Maybe block off the thermostat itself by wrapping it with tinfoil and reinstalling.

I had one once that did the same exact thing you describe, I was working 7/12s (out of town in Minnesota in February) and couldn't work on it. On the way to the mechanic's shop it magically healed itself. Turns out it had an air pocket in the cooling system, once that got out it worked fine for the rest of the time I owned it, about 6 yrs. Don't know how to get it out, just time and driving I guess, maybe the hose in the fill neck would do it. Hope some of his helps.
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