91 overheating questions

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tmorales509
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Car: 1991 nissan maxima gxe auto

91 overheating questions

Postby tmorales509 » Sun Nov 22, 2020 4:42 pm

So i noticed my car temperature getting hot and the heater blows only cold air. First thing i did was change the thermostat. That didn't fix it, so i changed the radiator next, that didn't fix it. I Notice that at first the heater does stat getting warm but after i drive it a little bit it will start getting cold again and the temperature gauge will start going up. I've tried bleeding air out by jacking it up and running with the radiator cap off but doesn't seem to do much. One question i have is someone told me that when you install the thermostat the little hole on it has to be in the 12 oclock position which i didn't do. Could that be the reason it still overheats or am i looking at maybe the water pump? Also the big hose at the bottom of the radiator doesn't get hot like the other hoses.


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VStar650CL
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Re: 91 overheating questions

Postby VStar650CL » Sun Nov 22, 2020 5:17 pm

You definitely have a flow problem if the lower hose isn't getting warm with a new radiator and a wheels-up bleed. The fact that the heater gets cold again means the thermostat is probably opening (the reduction in pump head when it opens reduces some flow to the core). It's possible your pump impeller has come loose on the shaft and is only providing a little flow. That's rare but it does happen. Does the engine overheat when you sit at idle, or only when you drive it? If it doesn't overheat at idle then the impeller is a good bet.

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tmorales509
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Re: 91 overheating questions

Postby tmorales509 » Sun Nov 22, 2020 5:30 pm

It does overheat at idle to, just takes a bit longer than when i actually try and drive it. I'm guessing it would probably come down to the pump if i changed the thermostat and radiator already?

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VStar650CL
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Re: 91 overheating questions

Postby VStar650CL » Sun Nov 22, 2020 5:49 pm

Yah, unless you have a clog in the block or a collapsed hose, something weird like that. You're clearly not getting much flow if the system is full but the lower hose is cold. I've seen hoses delaminate and collapse on the inside without looking squashed on the outside, usually from rusted-out spreader springs. If you haven't checked them you should, especially if they're old. It's messy, but you can check the pump by pulling the stat and sticking the lower hose in a bucket of water. You can also check the stat by disconnecting the upper hose and see if it goes from a trickle to a gusher when the engine warms up.

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VStar650CL
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Re: 91 overheating questions

Postby VStar650CL » Sun Nov 22, 2020 6:10 pm

Come to think of it, the stats on some of those old ones could go in backwards with a little force, and they won't work that way. You didn't have to force anything when it went together, did you?

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tmorales509
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Re: 91 overheating questions

Postby tmorales509 » Sun Nov 22, 2020 6:17 pm

No im pretty sure the stat is in the right way. I'm just referring to the little hole on the stat some people say it needs to be in the 12oclock position or else the air won't bleed right. I forgot to look at it when I put it in so there is a good possibility that its not in that position.

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VStar650CL
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Re: 91 overheating questions

Postby VStar650CL » Sun Nov 22, 2020 6:28 pm

It would bleed anyway if you front-jacked it with the engine running long enough to crack it open. I doubt that's the problem, unless it's a bad stat or you damaged it somehow. Here's a link to the stat and housing for the '91 Max just in case, it shows the proper direction:

https://drive.google.com/file/d/1dV3Zwd ... sp=sharing

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tmorales509
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Re: 91 overheating questions

Postby tmorales509 » Sun Nov 22, 2020 6:44 pm

Thanks for the diagram. I won't really have time to check it again until Wednesday or Thursday but I'll probably end up taking the thermostat back out and checking it. If it's good I'll just chage the water pump to. I'll get back here after. Thanks again.

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VStar650CL
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Re: 91 overheating questions

Postby VStar650CL » Sun Nov 22, 2020 7:22 pm

You're most welcome! Let me know what you turn up.

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VStar650CL
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Re: 91 overheating questions

Postby VStar650CL » Sun Nov 22, 2020 10:17 pm

Well, I stand corrected. Spoke with a friend who's more of a cooling guru than I am (I'm mainly electrical), and he tells me the 3L's were crazy critical about the bypass hole. If it isn't between 10 and 2, it's likely that no amount of jacking will crack the stat and let it bleed. So there's basically a 67% chance that's your problem.

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tmorales509
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Re: 91 overheating questions

Postby tmorales509 » Thu Nov 26, 2020 11:54 am

Thanks, yeah i had someone else tell me about that burp hole and im working on it right now. Will let you know if that was the problem.

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tmorales509
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Re: 91 overheating questions

Postby tmorales509 » Fri Nov 27, 2020 8:19 am

So corrected the tstat and bled the air properly and seems to be doing fine now. Heater is blowing hot air again as well. So far so good. :dblthumb:

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VStar650CL
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Re: 91 overheating questions

Postby VStar650CL » Fri Nov 27, 2020 8:26 am

Sweet, good to hear!


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