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1jz 240sx
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205 Posts
Discussion Starter · #1 ·
Hi guys, here's the deal. Gotta a 1j in a 240sx. But as of late, its been overheating. I just bought a brand new Koyo radiator and have 1.3 bar radiator cap. I doubt the radiator has an issue because its brand new. The cap, I'm going to get a lower rating cap, but haven't done that yet. Other than that, what could be the issue? What is the proper way to bleed or burp the system? This is how it over heats. If I'm just cruising either city or hwy, the temp remains at about 185-190. As soon as I mash on it, temp rises rather quickly to about 220 or so. Then it just hangs there and will start to come down very very slowly after a long time of driving. My theory is, if the fans weren't flowing enough it would overheat in the city, but be fine on the hwy. What you guys think could be the issue? oh, and its a new t-stat. Thanks for you help.
 

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You could have the first stages of a blown HG, which will cause those temps to go up when u get on it. Any white smoke coming out the exhaust that stinks real bad? You said...."As of late, it's been overheating." Does that mean it was fine a few weeks ago? I would be more concerned then of a HG or pump problem. Did you change the water pump? I have the same setup in my 1jz s13 but with a Mishimoto radiator and it never goes above 185. In fact, it takes about 25 minutes to warm up if I just let it idle in my driveway, air temps are about 75 though.
 

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1jz 240sx
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205 Posts
Discussion Starter · #5 ·
You could have the first stages of a blown HG, which will cause those temps to go up when u get on it. Any white smoke coming out the exhaust that stinks real bad? You said...."As of late, it's been overheating." Does that mean it was fine a few weeks ago? I would be more concerned then of a HG or pump problem. Did you change the water pump? I have the same setup in my 1jz s13 but with a Mishimoto radiator and it never goes above 185. In fact, it takes about 25 minutes to warm up if I just let it idle in my driveway, air temps are about 75 though.
No white smoke, and smells like it always has....like fuel :) It runs a little rich. Yeah, its was fine a few weeks ago. Went on a road trip and didn't have any issues and the most it would rise would be around 200 and a few runs, but it would come down fairly quickly. The problem started when I turned on the heater. The car temp was hella hot in about 10 mins of street driving. So I figured there may have been air in the system. But now, its just a constant issue.
 

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Acceleration
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The efans probably aren't flowing enough.

Have you been running them since day 1 of the swap, or did you start with a hydrofan/2j clutch fan?

You can always try burping the system, I know it's a common problem in the MKIII because the heater VSV is the highest point in the cooling system (Radiator cap is supposed to be), but I'm not sure how the setup is in the 240.
 

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1jz 240sx
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205 Posts
Discussion Starter · #7 ·
The efans probably aren't flowing enough.

Have you been running them since day 1 of the swap, or did you start with a hydrofan/2j clutch fan?

You can always try burping the system, I know it's a common problem in the MKIII because the heater VSV is the highest point in the cooling system (Radiator cap is supposed to be), but I'm not sure how the setup is in the 240.
I've been running electrics from day one, heck I even ran the stock radiator for two years with no issues. What the proper way to burp the system?
 

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i <3 supra
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jack up the front end of the car as high as you can, or park on a hill to where your radiator fill is the highest point of your cooling system. Then turn the car on and heater on full blast and let it idle and fill it as needed.

thats what i do and i haven't had any issues.
 

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I've read alot of people having overheating issue's using electic fan on SC 1jz swaps, i've heard putting the stock fan shroud on helps, how i don't know?
 

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Acceleration
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i've heard putting the stock fan shroud on helps, how i don't know?
The fans will be pulling air through the entire radiator when the shroud is on, as opposed to just the enclosed area where the fans are mounted when there is no shroud.

Is there any drawback to removing the t-stat completely?
The engine will take way too long to warm up, all the excess fuel may leak past the rings and dillute the oil. When it FINALLY warms up, you aren't giving the coolant the proper time to absorb the heat from the engine. Removing the t-stat is not a good idea.

Although you said you've had the efans for 2 years and they've been fine, were you boosting the car last summer (Since it's starting to get hot out here in CA), have you made any big changes since then that would affect the underhood temps/cooling system?

If the cooling system is in complete working order and the fans worked fine before and nothing has changed, I'd do a compression test next.
 

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s366 equipped
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I had the same problem after changing the radiator on my 1j sc. turned out to be a bad thermostat .(I overheated this engine like a mofo one night and it still runs great) I doubt its a hg or a pump but there is always that chance it can be so statr small .the last thing you should be touching is the head gasket.

Changing the t stat takes 10 mins .Now is a good time to convert your waterpump to the 2j if you did not do that already.
 

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1jz 240sx
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205 Posts
Discussion Starter · #15 ·
I had the same problem after changing the radiator on my 1j sc. turned out to be a bad thermostat .(I overheated this engine like a mofo one night and it still runs great) I doubt its a hg or a pump but there is always that chance it can be so statr small .the last thing you should be touching is the head gasket.

Changing the t stat takes 10 mins .Now is a good time to convert your waterpump to the 2j if you did not do that already.
Not real familiar on how to test for a good water pump. I know its not leaking, but is there a particular test to see if its pumping?
 

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1jz 240sx
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205 Posts
Discussion Starter · #16 ·
The engine will take way too long to warm up, all the excess fuel may leak past the rings and dillute the oil. When it FINALLY warms up, you aren't giving the coolant the proper time to absorb the heat from the engine. Removing the t-stat is not a good idea.


Although you said you've had the efans for 2 years and they've been fine, were you boosting the car last summer (Since it's starting to get hot out here in CA), have you made any big changes since then that would affect the underhood temps/cooling system?

If the cooling system is in complete working order and the fans worked fine before and nothing has changed, I'd do a compression test next.
How would not having a t-stat differ from running the car cold? About boosting the car last summer, yes I was. I used to be running the stock 240sx radiator with e-fans and never really had an issue. It would start to warm up on a long hill or something like that, but nothing really huge. I just recently put in a bigger aluminum radiator, and e-fans and it seems to be overheating very quickly. I'm going to try to run with out t-stat to see what it does after the car warms up.
 

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LAG?? Learn to drive...
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what water pump do you have on there? if you still have the hydrofan pump there im willing to bet the bolt is backing off the plastic part of the shaft,a nd that at lower rpms it has enought o move water, but once you build boot and increase water pressure that the fins jsut spin on the shaft, causeing water to stop flowing.. Or you have broken off some of the plastic fins and it cant keep up with the flow needed to cool it under boost. WHy toyota used plastic parts in the cooling system well never know.
 

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Acceleration
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I'm going to try to run with out t-stat to see what it does after the car warms up.
Thanks for listening to my advice.

Lets review:

1. Without a thermostat the engine will take forever to warm up and all the excess gas may leak past the rings and dillute the oil causing internal damage/excess wear.

2. Without a thermostat the coolant will not be given enough time to absorb the heat from the engine.

3. Without a thermostat the coolant will not be given enough time to properly cool down in the radiator.

4. Without a thermostat the temperature will slowly and gradually increase until it can no longer be cooled enough by the radiator and the engine will overheat causing further damage.

Just because you can run without a thermostat doesn't mean it's a good idea. It's a critical part of the cooling system and an engine will ALWAYS run better and last longer with the proper thermostat, as opposed to running without one.
 

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sounds like good advice to me, running it without a thermostat is such a ghetto fix and not really addressing the problem.
 
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