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Jay, Nissan Technician
Category: Nissan
Satisfied Customers: 20485
Experience:  20+yrs experience with Nissan & Infiniti Trained & Certified.Currently still working for Dealer
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1987 Nissan 300zx: thermostat, water pump and radiator..blow hoses

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I have a 1987 Nissan 300zx that overheats. I changed the thermostat, water pump and radiator. It continued to blow hoses. I couldn't figure it out. I finally did the touch test on the hoses and discovered after the car got hot the upper radiator hose was hot but the lower radiator hose was still cool and the hoses were swelling. It seemed like the thermostat was bad so I changed it. Nothing changed. I boiled the thermostat to makke sure it opened and it did. Any ideas why there is no flow? Should I just remove the thermostat?
Hello and thank you for using

How many miles on the car and when was the last time you replace the water pump?

Let me know, thanks Jay!
Customer: replied 7 years ago.
The car has 130k on it and I changed the water pump about two weeks ago.
Ok, just trying to get some history on the car. Since the upper radiator hose is getting hot and the bottom is cool, it sounds like there is a restriction in the radiator it's self. That is a sign of it. I would look into having the radiator checked. If it's causing the restriction and not allowing coolant to flow through it properly, then it will need to be replaced.

If you have any more questions on this, please feel free to ask. Thanks Jay!
Customer: replied 7 years ago.
I just replaced the radiator Saturday thinking that was the problem. No change. Any other suggestions?
How are you bleeding the coolant system? Are you bleeding it?

Let me know, Thanks Jay!
Customer: replied 7 years ago.
I'm not. How do I do that?

Give me a min and I will give you directions on how to bleed the coolant system. You may have a air pocket causing your problem.


Give me a few. Thanks Jay!

To bleed the coolant system, remove the radiator cap. Install the coolant bucket. Fill the bucket about 1/2 way. Then raise the front of the car as high as if it were on ramps. This way if there is air in the coolant system, the circulation brings it to the highest point. Then turn on the car, and put the heat on speed number 4, recirc mode on, and face mode. You may need to rev the engine a few times to move the coolant around to get the air out. After you have good heat, and little to no bubbles in the coolant bucket. Then the coolant system is properly bleed. You should have good heat when bleed properly. So when you put your hand over the vent and hold it there for 30 seconds, you get a slight burning sensation. That is perfect heat.


If you can't get a coolant bucket to help bleed the coolant system, you can make one. Here is a image of a home job.


Try this and let me know if this helps. Thanks Jay!

Jay and 2 other Nissan Specialists are ready to help you
Customer: replied 7 years ago.
I thought things were going well. After driving my car for 20 minutes it blew a hose again. The tempature gauge spiked past half, back to mid way and then it blew. What the heck is going on? Any ideas?
I know you said you replaced the radiator, but I wonder if it's defective. Another thing you can try is by pass the heater core so coolant doesn't circulate through it. Then try that.

Another thing you may need to do, is take a hose, and run the hose through the engine block and through the heater core, to see how the flow is. The Radiator I would take to have checked. Some times when manufactured, metal debris from construction could get caught inside and restrict like you are experiencing.

You do have a interesting situation. Keep me posted on what you find.

Thanks Jay!
Customer: replied 7 years ago.
At this point I am going to take it to a shop and let them test it.
That is what I would do. I would have a radiator shop check it. For the hose to pop off, and the lower hose to be cool, that sounds like a radiator.

Keep me posted, i am now curious on what they find.

Thanks Jay!