Rb25/30 Over Heating Issue.

[MBS206]

Hey all.

Currently my 25/30 has a bad overheating issue.

The car heats up nice and quick, but the skyrockets and fluctuates between 85 - 90degrees. The bottom radiator pipe stays cold, whilst the top is boiling hot. I have replaced the thermo stat 3 times, it now runs a genuine pump. I'm running the standard fan, and the air it is pulling off the radiator is cold, the only part of the radiator that is getting hot, is the top 1 - 2 inches.

I haven't seen the temp go above 90 degrees, even if the car is moving.

This issue has been there since the motor was put together.

Any help/ideas/suggestions?

Details below.

Currently I have an RB25/30

It's running the RB25DE head from an R32, with 240 degree exhaust, and 248 degree inlet cams.

The bottom end is a VL RB30 bottom end. The only mods to the bottom end (Other then being a fresh build) are ceramic coated pistons.

Running the fuel side is a bosch 044 pump, with a sard adj reg, and Bosch 036 Injectors.

Inlet mani is stock 25DE from an R32. Exhaust mani is a 6boost, bolted to a T04R.

Coilpacks are splitfire, plugs are gapped to 1.1mm

Running a plazmaman FMIC, and a BRAND NEW Radiator (The radiator has been run for 20 minutes, The old one passed away during testing to solve the over heating issue)

The pump is a genuine nissan waterpump, RB30. It's been pulled off, and inspected, it is brand new too.

I am kind of thinking that the standard outlet piping which is from 2 spots on the side of the head, which join into one pipe, and the one spot out the front of the inlet manifold, that join together, and then return to the radiator might need the pipes to the head blocked, and just leave the inlet mani side... Not sure though, and don't want to break anything.

The motor has ALWAYS had this over heating issue since it went in my car. Any help, ideas, suggestions, things to check or try?

This car is doing my head in majorly...

Please help.

Thanks heaps, Matt

[VB-]

i thought normal operating temp is 85-90 degrees? your thermostat isnt opening if the bottom hose is cold, so maybe its just not getting hot enough, even though to you it feels like the top hose is 'boiling'? only other hting i could think of is blockages in the block or something?

[chrissso]

Try running it without the thermostat. See what the temp is then.

[MBS206]

Chrisso: Without thermo, the temp sits at 60 - 70 degrees,

The issue with not running a thermo in an RB style motor, is the water divert in the back of the block, if it's not blocked whilst taking water from the radiator, I've been told it can hot spot the block. My mechanic refuses to tune it without a thermo in it, and as such, the car is at mine whilst we work out the issue (He was letting me work on it at his workshop for no charge, but workshop got full... )

The top hose is actually getting to a boiling temp, as 2 temp guages in the pipe say so, as does the laser gun, and a thermometer in the top of the rad.

[Adriano]

If the stock sender is reading 85-90 degrees, thats in the top hose? Just need to remember that boiling temp in a rediator is about 115degrees due to the pressure.

[MBS206]

If the stock sender is reading 85-90 degrees, thats in the top hose? Just need to remember that boiling temp in a rediator is about 115degrees due to the pressure.

The stock gauge is also telling me it is WAY too hot.

Even the mechanic is saying it is way too hot, especially for just sitting and idling.

[daisu]

Perhaps a blockage in the bottom radiator hose like maybe a rag/cloth was put up the hose to prevent stuff getting up there during rebuild and it was missed during reassembly?

It's a long shot, but we've all heard stories of people putting rags in inlet pipes only to forget them and they end up stuck in the throttle body.

Either that or the RB30 block has a blockage in the water inlet? Was the RB30 in running condition when it was pulled from the car? Did you pull the engine or was it sitting in someones garage/backyard/garden shed for an undetermined period before you bought it?

I don't know how the water galleries are designed, but I'd guess the bottom rad hose goes into the block and that is where the water pump takes it feed from? Perhaps take the water pump off again and check with the garden hose you can get water through there?

Edited September 3, 2008 by daisu

[MBS206]

Hey Daisu

Yeah, the bottom rad hose is the inlet of water TO the motor, and this is where the thermo also sits, and also where the waterpump pulls water from (Hence the bypass directly behind the thermo that gets closed when it opens.

When I had the water pump off, I blasted water through every opening I could find. From the top outlet pipe, to the water bypass where the thermo sits, to the point the pump pushes water through. They all flowed around and together... Weird... :S

Oh and the engine was meant to be freshly rebuilt (And every sign on it says it is a fresh rebuild also...)

Will pull the hoses off though and check for blockages, but it seems to be able to flow, as everytime I remove that pipe water pours out of it. Will removed and check though.

Edited September 3, 2008 by MBS206

[daisu]

Did you bleed the air out of the coolant using the bleed nipple on top of the inlet manifold?

[Adriano]

Are you using the r32 or r33 water temp sender?

[MBS206]

Are you using the r32 or r33 water temp sender?

It has both R32 senders in it.

Is there a difference?

Daisu: I have been yes, will be doing more soon, following the service manual at the moment to bleed it, need to cool car back down again.

[R34GTFOUR]

If you take the radiator cap off, start the car and get it to operating temperature, can you the coolant flowing along the top tank?

Have you had a leakdown test done on the motor to make sure the headgasket isnt leaking?

You're running a genuine pump, but are you running a genuine thermostat? I've had several dodgy aftermarket thermostats, so from now on i never use anything but genuine.

Since the radiator is new (assuming its totally clean), there is only one reason why the top will stay hot and the bottom cold which is the water pump isnt sucking the coolant. Since its a brand new genuine pump we can be safe to assume that the pump itself is ok, which only leaves the one restricition between the pump and radiator and thats the thermostat. Since you took the thermostat out and it ran at 60-70 degrees, i would say that for what ever reason the thermostat is shit (even though its your third). I would boil a cup of water and stick the thermostat in it and time how long it takes to open.

[MBS206]

R34 GTFour: The current thermostat is genuine.

I decided after the second, that I'd try a genuine one. I'll time it on Saturday to see how long it takes to open. I know at 90degrees celcius it should be open 10mm (According to the service manual)

And I've been squeezing the bottom hose, and you can feel it pressure the top hose (squeeze top hose first) from the radiator side, as though the thermo wasn't open. Very strange...

[R34GTFOUR]

If the thermostat is rated to 90degrees, and you car runs between 85-90, whats the problem?

[MBS206]

If the thermostat is rated to 90degrees, and you car runs between 85-90, whats the problem?

Thermo is rated at 76.5

The service manual gives a length it should be open at 90C.

Car should be sitting around 77 - 78 when idling. Gauge in the dash is off the scale. As is ECU, and a thermometer.

[R34GTFOUR]

Thermo is rated at 76.5

The service manual gives a length it should be open at 90C.

Car should be sitting around 77 - 78 when idling. Gauge in the dash is off the scale. As is ECU, and a thermometer.

haha ok, i re-read the post a few times with a confused look on my face

My bros gtst use to run between 78-80 degrees according to the powerfc, so 90degrees might be a tad warm. Definately not hot enough to do damage, but if your coolant is boiling in the top tank that means its getting hotter than 90degrees, more like 110+ which is definately a problem.

Since there is such a big drop in temp with no thermostat, i would still be inclined to think its thermostat related.

Check the specs of the thermostat with the manual, and if you have an accurate gauge heat some water upto 80degrees and see if it fully opens at that temperature.

After that i would order a low temp nismo thermostat and see what happens

[Adriano]

76.5 is the cracking temp of the thermostat, i would expect it to have an operating temp of 85 deg. The r32 and r33 temp sensors are different , and have different scaling, hence the high reading.

[bubba]

I can confirm R32 and R33 senders are different and have different scaling. When I built my 30 I snapped my 32 sender so whacked the 33 sender in there, ECU thought it was in cold start all the time!

[MBS206]

Adriano, Bubba, I shall replace the temp sensors. If you guys solve this one, I owe you both a beer!

[MBS206]

Adriano, Bubba: The beers that I owe you, have to go on hold... Blew the HG apart tonight...