Overheating

[Ryan06sti]

So i have the q45 swap in my 240sx. Im having an overheating issue. I just got the car an with this issue.. i go to check if theres a thermomstat. There isnt. So i leave it that way. Just cause im already overheating without one.... i check the water pump. Looks good. So i put my fan on constant, to see if it will just stop overheating, but doesnt..... my question is without the thermostat in will this engine overheat.. seems the coolant travles pretty fast threw the radiator. Does it not have time to cool? Ive done this 100 times with other cars just to run threw possiblities. None of which ive ever tested an had this issue. It does also have a aftermarked think radiator. Thanks for reading

[Q451990]

to NICO!

I wouldn't think it would overheat without a thermostat, but I don't know for sure because I can't recall anyone ever trying it. When it's overheating are the inlet and outlet hoses both hot?

[Ryan06sti]

Yes. Both are hot. An radiator. Ive never had a overheating issue like this. Thats why i was wondering if the thermostat gave it enough time to cool before coming back into the motor. I went for a 10 hour event an made 2 laps both in which cut my power an just drove around the trade. Bubbling out of the overflow. It happens more when i beat on the car than when its sitting idle. Which is also oppsite and weird.

[3Q Jay]

Yes. Both are hot. An radiator. Ive never had a overheating issue like this. Thats why i was wondering if the thermostat gave it enough time to cool before coming back into the motor. I went for a 10 hour event an made 2 laps both in which cut my power an just drove around the trade. Bubbling out of the overflow. It happens more when i beat on the car than when its sitting idle. Which is also oppsite and weird.

why would you think this is abnormal??
how do you know you have sized the correct heat rejection capacity of the radiator?

[Ryan06sti]

Yes. Both are hot. An radiator. Ive never had a overheating issue like this. Thats why i was wondering if the thermostat gave it enough time to cool before coming back into the motor. I went for a 10 hour drift event an made 2 laps both in which cut my power an limped around the track. Bubbling out of the overflow. It happens more when i beat on the car than when its sitting idle. Which is also oppsite and weird.

[Ryan06sti]

Sorry for the repost. It just seems like its getting heat soaked an im lost. Been messing with it for three months

[Ryan06sti]

An the radiator doesnt have a fill on it. Its all done by the overflow radiator is solid besides a vent up top.. honestly i dont know what temp it would reject.

[Skibane]

So i put my fan on constant, to see if it will just stop overheating, but doesnt

Is the electric fan the only fan that's present? No belt-driven mechanical fan?

You're still using the original 240SX radiator (which was designed to cool an engine with roughly half the displacement - and half the number of cylinders - as the Q45 engine)?

Regarding the lack of a thermostat - I'm not even sure it's possible to circulate coolant fast enough through a radiator to cause overheating. At higher circulation speeds, what you lose in heat rejection on each pass through the radiator is probably made up for by having more passes through the radiator per minute.

[3Q Jay]

I should have clarified my earlier comment. It sounds like the engine is doing exactly what one would expect it to do if you beat on it with an undersized cooling capacity.

fwiw, even a perfectly maintained vh45de in a stock g50 chassis with proper air flow, baffling, clean fins, foam seals and an oem pedigree radiator *will* see temperature climb if constantly operated at 4000+ rpm.
so if you intend to exceed the original design parameters of the vh45de (not just the S13/S14) cooling system, you must upgrade the design to match your intended use.

[Ryan06sti]

I think i may have figured it out. Havent tested it but i pretty sure. I bought this car in"running" condition. So i was pretty much lied to. Dont think its ever moved once since swapped. The owner had this rad custom made. In which he cut out the radiator cap an just made a hard line elbow that goes into the over flow. So theres two lines that run into the cooling system from the overfow with no spring loaded caps to close of the system. Which i was under the impression that the overflow cap was somehow pressurized. Well today i found out its not the overflow tank is open to atmospher. So this hole coolant system never gets pressurized . An goes out the weakest stop which would be the overflow. I hope so atleast....

[Q451990]

It certainly sounds like you're on to something.

[Ryan06sti]

Still overheat. After 30 mins of idling shuts down puts it in like limp mode

[J30tChumpCar]

I am actively endurance road racing this engine in a (marginally)street legal j30 for 1.5 years...without a fan! Racing speeds are plenty for airflow, heck 35-40 mph is enough to drop temps after a long traffic light or mc donalds drive thru


First off, you need a thermostat to block the "warm up loop" I will call it, factory design is to bypass the rad to recirculate coolant for both smog and faster heater operation when engine is cold(flat disk on the tail of thermostat does this), you can drill the thermostat with (2) 3/16 holes to partly disable but let coolant flow through proper channels, this will keep it from fully closing/sealing and trapping air in a improperly designed setup.
Saying that
Trapped air, a improperly designed cooling system can easily trap air and cause all sorts of overheating issues, you really need to make sure this is not your problem. I can not stress this enough!

Custom rad, measure the core dimensions and thickness, compare to a stock q45 rad to see if its at least as big, I chose a 5.0 4x4 explorer rad, it does the job for me but was rather difficult to fit in a j30, prob wont be close to fitting your car.

What are your competitors doing to cool their 240/v8 drifters? Time to scope other peoples cars while in the pits and chat about the other guys setups.

And most likely, engine condition

Overheating till stall/limp at idle of 30 min with fans on not good news,I know this is a stupid question but you never mention temps, just limp mode, do you have a decent gauge? Just yesterday we competed 12+ hours on a 95 deg day and had issues, it never went limp even at 220, a little lethargic but not a reason to stop.
Is it possible that between you and the last guy the thing has popped a headgasket? Perhaps drop by a NAPA to get a professional kit like this, https://www.amazon.com/Lisle-75500-Comb ... B0007ZDRUI

When used properly it is a very reliable way to decide.

[Ryan06sti]

Temp gauge wasnt working . I ended up fixing it temps ended getting upward of 250 so i havent ran it since. I pulled off my intake manifold to make sure the cross over lines hard fluid . Lines to the head an cross over all haave fluid an it seems to be flowing fine