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Old 08-10-2014, 05:09 PM   #1
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Default Temperature Help

Hey guys,
I'm restoring my father in law's 1987 4cyl Base D21 and am having a problem with the cooling system. Here's what I've done so far:
Replaced upper and lower radiator hoses
Replaced temp sender
Replaced thermostat. Stock is 160 I think, but I put a 180 in there
Replaced water pump and fan clutch
Flushed out the system with detergent once, then flushed out radiator with a garden hose on two separate occasions
New v-belt
New overflow reservoir

After putting everything back together I filled the system with water to check for leaks. There didn't seem to be any so I took it for a drive to warm it up. Fastest I went was 45 or 50, but the gauge kept climbing. I didn't let it reach the max temp, but it got close so I pulled over and popped the hood. The engine bay didn't seem unusually warm to me, but I'm no expert. Please help, I'm at a loss for what's wrong with this truck!
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Old 08-10-2014, 05:21 PM   #2
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I'm not sure if the z24 has an air bleeder screw for the coolant, but look on the intake manifold near the front and see if there is one near the coolant temp sensor. Trapped air can cause it to run warmer than normal. You can also try parking with the front of the truck much much higher than the back to try to get the air to work its way to the radiator. FYI, normal operating temperature is just below half mark on most Nissans.

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Old 08-10-2014, 05:33 PM   #3
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Wow thanks for the quick reply! Sounds like it might work. I'll check that as soon as I get the chance.
I figured that maybe the temp sender wasn't plug and play and needed some calibration or something. Either that or my gauge was going bad.
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Old 08-10-2014, 05:35 PM   #4
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My 87 VG30 had a air relief screw in the upper hose but do not see one on the Z24 engine or in the FSM.

Most times if you have an air bubble or air pocket in the system you will not get good heat ( in the cab), make sure when you fill the system you have the heat on so the water will circulate into the heater core and give a proper reading on whether the system is full or not.
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Old 08-10-2014, 05:42 PM   #5
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Ok so it sounds like I need to be filling the system when the engine is running. I've been filling it while off. Won't it damage the engine to run it without coolant?
Like I've said, I'm far from an expert.
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Old 08-10-2014, 06:02 PM   #6
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you can fill it when the engine is off, once you get all the coolant in you can, start the engine, turn the heat to on and turn the fan on high, you need to wait until the thermostat opens, when it does the coolant level in the radiator will most likely drop, than add more coolant, slowly, so the air can escape, you may want to do as was said and jack the front of the truck up to make the radiator cap area higher than the engine.

when you add all the coolant you can, top off the overflow bottle to the proper level ( line on the tank), put the radiator cap back on and let it run until the gauge comes up to normal temp, check the heat in the cab, if it is hot you are probably good.

If the gauge keeps rising past the middle there may be a problem, since all the related parts are new there shouldn't be any issues.

Shut the truck off and let it cool, you can check the coolant level in the radiator once the engine cools, if you have to take the radiator cap off while it is hot, use a very thick towel, folded over so it is multiple layers thick, put it over the radiator cap and slowly loosen the cap so any pressure can bleed off, BE CAREFUL !!!
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Old 08-11-2014, 05:29 AM   #7
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As others have said make sure there's no air trapped in the system.... when you installed the thermo did you have the jiggle valve pointing upwards? I ask this because it needs to be..... also pressure test the radiator cap to see if its holding pressure because if its not the boiling point of the coolant will be lower and water boils at 212 degrees which is close to what most motors run at and at that point you have water pump scaviging.... run the motor with the cap off and see if the coolant bubbles or there's hissing in the overfloe... if so then combustion gases is mixing with the coolant and its either a bad head gasket or cracked head.

Most likely its something simple but I thought I would state what others haven't yet.

Good luck and let us know what you find
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Old 08-11-2014, 05:17 PM   #8
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I see you replaced the coolant temp sender(1wire), however what about the coolant temp sensor(2wire) for the ecu?
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Old 08-11-2014, 09:34 PM   #9
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+1 On checking your thermostat direction. Like filthy forever mentioned, with it installed backwards you'll prevent flow and get no circulation. May wanna check it before you try to get all the air out since that would open the system back up.
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Old 08-12-2014, 03:44 PM   #10
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Thank you all for the great responses! Once I took all the air out of the system the gauge went back to functioning normally. I guess I just didn't know how to fill a radiator properly :/
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