Coolant sytem question.

[Cpt_Impossible]

I have been dealing with an overheating problem on my RB20 swapped S13 for a while. The odd thing is that it only does it on the freeway. I started with stock RB20 radiator and two 12" fans 2000cfm each.

At first I think maybe the radiator is plugged up so I flushed it and reburped it but that didnt help.

Second I noticed my JDM radiator cap that came with the car looks a little shady so I switch for a brand new one at stock pressure rating.

Third I think maybe because of the FMIC the radiator isnt getting enough air. I already had an upper radiator cooling panel so I fabbed a lower one.

This seemed to help barely but the problem didnt go away.

So fourth I think maybe my radiator core is jammed up or damaged or just not big enough to do the job so I upgrade to a S13 KA Koyo piece. Problem still doesnt go away completely. After burping and filling with a 66% water 33% antifreese and a bottle of water wetter I have it to the point that it will run ok on the freeway but sometimes goes over the halfway mark on the stock gauge and opens the cap on the radiator. I can tell it isnt just a faulty gauge because the coolant level rises in the resivoir.

I tried installing a cyberdyne digital water temp gauge so that I can tell how long it takes and what conditions cause the problem more accurately but the NISsport adapter doesnt fit in between the koyo and the stock water temp kneck on the RB20, there is physically no room. So I have the gauge mounted and the sensor routed to where I want it but not installed yet until I decide where to tap it.

So after all this I start noticing that the lower radiator hose to thermostat is cool to the touch even though the top is hot. This led me to believe that the coolant wasnt flowing but rather rising to the top when it gets hot. So I replaced the thermostat (which was done at the tim eof the swap with a generic one) with a real Nissan Z32 TT thermostat. I also used a mix of Honda OEM coolant (suposed to be the best for aluminum radiators) water and water wetter. I just finished burping it after letting it cure for 24 hours and then drove it around a while. Temperature seems to hold fine on the freeway. I turned the heat all the way off and blasted a few onramps and cruised at 3k afterwards. This is normally where I saw problems. The temps seemed to hold fine but without the digital unit its hard to know for sure seeing as the stock unit registers as just under halfway for a wide range of temperatures it deems short of overheating. So after beating on the car a while I notice that the bottom hose is still cool to the touch.

I know this was a realy long story to ask this question, but should my bottom radiator hose be cool to the touch? Is this a sign that my coolant isnt flowing or that all my cooling mods are doing a great job?

-Koyo-No AC so no condensor-upper radiator panel-lower radiator panel-Brand new radiator cap-Brand new thermostat -two 12" 2000cfm fans-Mix of Honda OEM coolant with water and water wetter

If the thermostat isnt fixing the problem then there are only so many things left as far as I see it. Either the water pump fins are shredded, the coolant passages in the engine are jammed, or the headgasket is blown. I dont see any air coming up through the resivoir nor do I see any oil or gasoline in the coolant. Should I move on to the water pump or is it normal that my bottom hose is cold?

[Carl H]

did you replace the thermostat and waterpump when doing the swap?

[kouki-gymkhana]

You should perform a leakdown test. I had a blown HG with no obvious signs (ie white smoke out the exhaust or bubbles in the coolant). Given what you have described, it sounds like you do not have adequate flow through the radiator, either because the thermostat is still faulty (even though you've said you already replaced it), the Koyo is blocked (unlikely since it's new) or the waterpump is toast. Unfortunately, it looks like you're going to have to pull things apart to see what's really going on. You could try removing the thermostat altogether and see what happens after a test drive. That would at least let you rule in or out the thermostat as the culprit.

Good luck and keep us posted. BTW, as you've already pointed out, you should NEVER rely upon the stock temp gauge because it is incredibly inaccurate. I was seeing 85 degrees C on the highway with a blown HG and the stock gauge was reading "C" the whole time.

[USMCgetsome]

i'm still having the same issue as he is. I have a 14in pusher 1250ccfm and a 12in 1500ccfm puller on the radiator. Changed to a nismo t-stat. Ghetto rad cap and new water pump with begining of install from courtsey parts nissan. I think the water pump isn't doing enough. On highway it stays cool but when i come to a stop it comes up slowly even with the fans on. wierd.

[Cpt_Impossible]

My car sproblem was heating up on the freeway and then being a-ok at idle or stop. I can blast on it all I want at low speeds, but holding 50mph plus is where i was having problems.

The water pump was never changed.

[Carl H]

change the radiator cap, either a genuine nissan or something uprated...i had a bad cap on mine and it was causing it to not hold pressure and overheat.

[Cpt_Impossible]

OK I guess I can try that. The one on there is brand new but generic Schmucks.

[minivan_don]

as mentioned, it could be a block in the cooling system...

to test this, you can take your rad cap off while the engine is running and see how fast the fluid is moving. if its not moving, it can be a blockage OR the fins on the pump are non existant.

if its not the pump, which i highly suggest you replace to rule 1 more thing out, you can head to a local rad shop to get your system pressure flushed.

i dont think its a tstat or obviously the rad/fans. hopefully you had the heat on full and the front end elevated (like on a drive way) when bleeding the coolant system.

[Cpt_Impossible]

Yeah I have learned my lessons with burping in the past. When I take the radiator cap off with the car running it just starts overflowing.

[minivan_don]

you might need to remove some of the coolant ... so it sits like 2" below the cap ... then see how fast its moving

[Darius]

Replace the water pump.

You've done a good job of trouble shooting 90% of the parts in the cooling system already

[Eikon]

Replace the water pump.

You've done a good job of trouble shooting 90% of the parts in the cooling system already

I went through the same steps as you and finally found it was the water pump... zerothread?id=97865

[Cpt_Impossible]

So I took off the radiator cap and had it so the coolant was not quite to the top of the radiator. Started the car and let it run for about 20 seconds. It doesnt seem to flow at all, rather it just starts rising. After about 40 seconds it is flowing over. Is this normal? If it isnt I am thinking maybe there is a blockaged in the passage and rather than slow circularly it just pushes it out the only place it can, the cap.

What are your guy's thoughts? Is it normal to just overflow with the cap off?

[Cpt_Impossible]

anyone?

[Darius]

If it is overflowing, it sounds like your water pump is at least creating some pressure. Drive it to a place where they do cooling system flushes. Typically they are pressurized and force clean water through the engine. Some might just do the garden hose in the radiator cap method, so you get what you pay for.

[Cpt_Impossible]

Thanks, Ive thought of doing the garden hose method on my engine myself, but it doesnt seem like it would be worth it for the little amount of pressure and cleaning power it has. I will set up an apointment to rule that out. Its cheaper than the water pump if it is my problem, and good maintenence even if it isnt.

[Cpt_Impossible]

Reading the aussie forums they say that there are two (2) bleed points on the rb20det. One is the one on top of the intake mani, but I cant find the second one. The FSM says its in front of the glovebox which is vague. On the forums they say its tee'd off of the heater hose.

"You have to bleed the air out the system. The R32's have two bleed points, one for the heater that is T'd off the top heater hose near the drivers side. You can bleed the plenum bolt as much as you want but it will still overheat IF you don't also bleed the heater hose."

Anyone know where this is?

[USMCgetsome]

soo i took off the main hose off the oil cooler and put a water hose in it and watched it purge the bottom end of the block. So i refilled it and burped it and guess what. while driving was stable at 67-70c and i had the fan controller set at 82c. Coming to a stop it would reach to about 84-85 then come back down to 78-79c. So golf clap to the garden hose trick but not at the radiator entrance.