SR20DET overheating on freeway/ highway

[kylekinnamon1989]

i just did an sr swap. i removed the thermostat during the break in period because i rebuilt it. on the freeway, driving about 65+ it overheats but as soon as i get off the freeway it temp drops. i was told not having a thermostat could cause that due to the water flowing too fast.. so i installed a new thermostat. now it overheats even faster on the freeway, but not normal driving on the main roads. i also replaced the radiator cap. still overheating.. please help. i have a 14" electrical fan on a switch running all the time (while driving) and removed fan clutch.

[JDizzle]

How are the fans set up? Push/pull, inside/outside? Do you have a large intercooler blocking air? Are you running a shroud and how many CFMs are your fans rated for?

[kylekinnamon1989]

Inside, pull. No fan shroud. And I do have a fairly large intercooler which could be potentially blocking airflow

[OutToWinPAHC]

Put the T-stat back in, bleed it properly and then try. When you remove a t-stat the water moves too fast and does not not cool.

[kylekinnamon1989]

No offense"outtowinpahc" but read the entire post before posting

[OutToWinPAHC]

Good call, my turn.... use the search function "overheating," 240sx gen, 240sx tech and SR, select search titles only, select topics only. Good results, sounds like air to me then.

[Chaluska]

definatly check out if the thermostat is opening up or not, its possible to get a defective one from autozone/nissan/advance auto where-ever.

wait, did you say you have 1- 14" fan?

thats definatly not enough, the radiator is like 29" across, the 14" fan only covers half of that, the other half is not being cooled, and will eventually let enough hot water by to overheat the system.

the radiator needs to have solid airflow across ALL OF THE FINS, not just half. snag another 14" fan, or get a set of altima/maxima fans, or a taurus fan.

[Chaluska]

Good call, my turn.... use the search function "overheating," 240sx gen, 240sx tech and SR, select search titles only, select topics only. Good results, sounds like air to me then.

^^ and this

[kylekinnamon1989]

See the funny thing is, I did use the search! Thats how I figured out putting the thermostat back in should have worked, unfortunately it did no which brings me here.... All the results I have read had nothing to do with driving on the freeway, having a thermostat, having bled the system and still over heating.

[kylekinnamon1989]

definatly check out if the thermostat is opening up or not, its possible to get a defective one from autozone/nissan/advance auto where-ever.

wait, did you say you have 1- 14" fan?

thats definatly not enough, the radiator is like 29" across, the 14" fan only covers half of that, the other half is not being cooled, and will eventually let enough hot water by to overheat the system.

the radiator needs to have solid airflow across ALL OF THE FINS, not just half. snag another 14" fan, or get a set of altima/maxima fans, or a taurus fan.

Also, the thermostat must be working because if it was not working then it would overheat with regular driving as well. I have only one fan, yes. But I would not be able to fit another fan because my intercooler piping is in the way in the engine bay and there iys a/c components in the way if the front of the radiator.

[grayslinky]

kylekinnamon1989,
did you ever get the freeway problem solved? I am having the same problem. If I turn the heater on I can get the temperature to stabilize, as long as I dont take the rpms past 4000.

[Gabes13]

definatly check out if the thermostat is opening up or not, its possible to get a defective one from autozone/nissan/advance auto where-ever.

wait, did you say you have 1- 14" fan?

thats definatly not enough, the radiator is like 29" across, the 14" fan only covers half of that, the other half is not being cooled, and will eventually let enough hot water by to overheat the system.

the radiator needs to have solid airflow across ALL OF THE FINS, not just half. snag another 14" fan, or get a set of altima/maxima fans, or a taurus fan.

The funny thing is that it's overheating on the freeway and NOT in the city. Technically, you dont even need to run a fan on the freeway; at 65+ mph you're probably blowing through more air than one fan. If its over heating all the time or just in the city then I could see your reasoning, but since it's not, your "1 fan is not enough" claim doesn't make sense.

Op, hows your radiator cap? is it holing pressure? Either way, it sounds like you have air in the system. Bleeding it out can be a b****, i know it is for rbs, so you might want to invest in a swirl pot.

[4cefed]

I have a couple suggestions.

1. If there is any question about weather the thermostat is working, you could try removing the plunger from the thermostat housing and installing the housing. There is enough restriction with just the housing to get proper flow.

2. Are you sure the timing is good? Having the timing off just a bit can cause massive overheating.

3. Water pump might be going bad.

4. Still have air in the system. For some reason, bleeding these things sucks. I can't remember if there is a high point vent on the coolant system. If there is, try getting a hose barb on it and use a hand vacuum pump to get the air out. My SRT-4 came with an actual brake bleeder in it, super easy to apply vacuum then close the bleeder. Under vacuum, you can loosen the radiator cap and draw coolant toward the vacuum source and close the cap again. Top off the radiator after a run cycle.

[Hijacker]

This is an old post, and I doubt we'll hear from the OP on his issue

Gray, what you're describing sounds like a faulty pump to me. SR pumps are notorious for cavitation at high RPMs, so to hear your issue is relating to motor speed makes me think either the pump is going bad or there is a small air bubble in the system working against you. A pressure drop will cause the same issue (either via a bubble or a bad cap)