Rb26 Temp Rising And Falling Rapidly

[SCRMER]

Hi All,

I wanted to ask for some advice as i have come to my wits end with this issues i have been having.

The premise is, i have a r34 gtr that has had a rebuild of the bottom end. Pistons/Rods etc. The head was left untouched and really the only thing else that was change in the motor was the comp ratio up to 9-1. To go with it all i had upgraded to a new KOYO radiator and replaced all the hoses, thermostat and water pump to new just to give it all a freshen up.

Motor started up first go, and runs great. Compression is good, doesnt miss a beat in terms of how it is running and how the tune is.

The main issue is the temperature. It will sit in the 60's for a while once it has started warming up, then rapidly rise to around 80 in the space of about 3-5 seconds. Give the car some revs and it then drops rapidly down to 60's again. It will stay there for 30 seconds then rise up to 100 in the space of 3-5 seconds, again give it a few revs around 3k, it drops off back into the 60's in the same amount of time. Then will rise up to 110, and back down then 120 and back down until it will sit at 120 and you need to turn the car off and let it cool to start the process again.

Now what have we done to trouble shoot?

1. First up it sounded like a sticking thermostat since it is new. Took it out put it in hot water and saw it barely open so naturally we replaced it and same problem. Tested the new one we replaced and was opening fine. Got a 3rd thermostat and still did not solve the problem. So we are ruling that out.

2. Thought there may have been some bleeding issues with the motor as it sounded like a air pocket was doing the rapid temp rise and fall as RB's can be a little troublesome to bleed. Spent 2 days trying different methods such as having the front jacked up, heater on, letting it idle and cool down etc to bleed it and still have the same issue

3. Tried a second new water pump. Didnt solve the problem

4. Pressure tested the Radiator and all was fine

5. Vacuumed the system, all fine, problem still persists

So now we are not sure what to do. Not sure where the problem is. Dont know if it is the new radiator that is causing the issue or is it something to do with how the motor was built. My mechanic is just about to pull the motor back out and take a look at the head gasket in case something is wrong there as we both can't figure out what to do.

Wondering if anyone has come across a problem like this or has any suggestions to what we could try before having to pull everything back out again

Cheers

[GTofuS-T]

Have you considered that it may be a faulty temp sender or gauge?

Is it the factory or aftermarket gauge? where is it tapped into?

[Hadouken]

you sure there isnt a dickload of air in there?

[SCRMER]

Considered it yes. The MFD, standard gauge and Power FC all showing similar levels

You can feel through the hoses when it's heating up and cooling down though

[GTSBoy]

Have you considered directly measuring the resistance of the sender as you go through the charade? The temperature may not in fact be moving at all (if the fault is at the gauge for example). Or the sender could be crook, in which case you'd see its resistance going up and down, but would not see it with a different sender inserted there.

etc.

[SCRMER]

you sure there isnt a dickload of air in there?

With the amount of bleeding we done, and the water that it took on you'd think there isnt. That was our first point to try at the start but after we bled and bled and bled the system it seemed like we were done. We tried it from scratch multiple times.

[SCRMER]

Have you considered directly measuring the resistance of the sender as you go through the charade? The temperature may not in fact be moving at all (if the fault is at the gauge for example). Or the sender could be crook, in which case you'd see its resistance going up and down, but would not see it with a different sender inserted there.

etc.

Honestly no, but both hoses are getting hot and cold as it is going through this process. The top not so much of course but you can feel the temp change

[GTRPSI]

What does it do when the car is cruising at a steady 100?

If its not going up and down while holding a steady high speed, it may be the clutch fan........sometimes they dont lock on till the temp gets too high, when on they pull the heat from the rad dropping temps.

A steady 100Kph should see a good natural air flow ruling it out, if it continues to climb and fall its not the issue.

Next step is like previously mentioned, check for air in head by bleeding.

[89CAL]

I was going to say something about the fan. Not sure if its running the stock clutch fan or an aftermarket electric fan setup but would be good to know what its up to. I dont believe it can be causing the issue, it sounds like to much of a rapid change in temp, but it may be largely contributing to it

You didnt install an N1 water pump to the car?

Trying to think outside the box because it sounds like youve tried doing everything right here

[SCRMER]

What does it do when the car is cruising at a steady 100?

If its not going up and down while holding a steady high speed, it may be the clutch fan........sometimes they dont lock on till the temp gets too high, when on they pull the heat from the rad dropping temps.

A steady 100Kph should see a good natural air flow ruling it out, if it continues to climb and fall its not the issue.

Next step is like previously mentioned, check for air in head by bleeding.

We never got it to those speeds. Just normal driving around the streets. It performed the same whether it was going 60km/s or just idling. Temp would rise and fall at the same rate. Everything i read tells me it is air, but we can't find any air left!

[SCRMER]

I was going to say something about the fan. Not sure if its running the stock clutch fan or an aftermarket electric fan setup but would be good to know what its up to. I dont believe it can be causing the issue, it sounds like to much of a rapid change in temp, but it may be largely contributing to it

You didnt install an N1 water pump to the car?

Trying to think outside the box because it sounds like youve tried doing everything right here

Only using standard Nissan pumps. Also using the standard clutch fan.

I've had heating issues in my other RB's that have used thermos but that is because they were not wired up right and it would be a gradual increase in heat. This is just bizarre. How quickly the temp goes from hot to cold is something i have to seen and can find any info on. The fact it will get to a point where it just can't be cooled unless the car switches off and the pressure in the cooling system dies down just points to air. But for the life of me, can't find any after everything i have done

[GTRPSI]

Ive seen clutch fans fail where temps use to be all over the place, running it at 100 on a freeway will provide a steady flow of air to rule out the fan.

If it continues to go up and down its not the fan (unless some rubbish has blocked the radiators air flow)

[89CAL]

Yeah but you dont usually see a rise in temp that rapid. My clutch fan was had it and when parked near a wall etc on a hot day it would on rise at say 1 degree per 10 seconds (when already at operating temp)

I would get either an IR temp gun or a temp probe and verify the sensor is working properly, then make sure coolant is flowing accross the radiator and try and bleed again. Is there a special trick with bleeding RB26's? I havent played with one for a while

[SCRMER]

Yeah will have to keep trying to above and see what the results are. I just hope i dont have to pull the motor out again and tare it all down to figure this out!

[iruvyouskyrine]

Did you change any of the coolant lines under the inlet manifold at all? Or did you route any differently?

[SCRMER]

Did you change any of the coolant lines under the inlet manifold at all? Or did you route any differently?

No they are all still the same but worth a shot to double check how they are run

[Hadouken]

How did you bleed it op?

[R31Nismoid]

Have you considered directly measuring the resistance of the sender as you go through the charade? The temperature may not in fact be moving at all (if the fault is at the gauge for example). Or the sender could be crook, in which case you'd see its resistance going up and down, but would not see it with a different sender inserted there.

etc.

Yep, this is what I would be checking first... A 20 degree change of temp in 3-5 seconds is utterly impossible from a heating the system point of view. There is no way you can heat litres of water that fast, and then cool it the same - in an engine bay.

[SCRMER]

Yep, this is what I would be checking first... A 20 degree change of temp in 3-5 seconds is utterly impossible from a heating the system point of view. There is no way you can heat litres of water that fast, and then cool it the same - in an engine bay.

I agree with what you are saying and it's a good point. But this issue seems to be with water getting stuck around certain points of the motor. It's like it gets stuck around the thermostat and then it releases after a certain point or even like an air pocket that has heated up causing massive temp jump. Once it releases then bang everything is rapidly cooled until it builds up again like that.

Temps appear to be different all around the cooling system as this process is underway. it's like something is stopping the water from free flowing all throughout the motor and as the motor gets hotter and the pressure rises in the cooling system, it get's harder and harder for it to push that water around the be cooled.

You'd think it is something stupid we have missed. I believe my mechanic is going to pull the motor out this week to see what's happening around the head gasket. Lucky it isnt going to cost me anything! Feels a bit extreme though

[Ben C34]

I'd pull off waterpump and check for shenanigans before pulling engine