Head Temperature

[Roy]

Ok, so i run std radiator and there is always talk about what temp the coolant should not exceed.

Looking around the net i cant find any info on what general temp an alloy head cannot exceed, ditto RB series engine.

I have just bought a new probe that will measure head temperature, i always pull the pin when the coolant temps nudge 90-100. The actual head temp whoudl give me a better indication when to back off...shouldnt it?

[Sydneykid]

Hi Roy, I am not sure that I completely understand the question. It is not the maximum temperature that causes cylinder head or head gasket issues, it is the temperature differential that causes warpage or, in extreme cases, cracking. For example exhaust ports can be upwards of 800 degrees C, water jackets max is around 110 degrees, inlet ports 60 degrees, combustion chamber temperature etc

So where you place the sensor determines what temperature you are likely to see.

cheers

[Roy]

Oh, I was goign to put it under the a spark plug...but by the sounds of it is a silly idea. Perhaps ill just use it to measure another temp?!?!

[s13rb26]

Hi Roy, I am not sure that I completely understand the question.  It is not the maximum temperature that causes cylinder head or head gasket issues, it is the temperature differential that causes warpage or, in extreme cases, cracking.  For example exhaust ports can be upwards of 800 degrees C, water jackets max is around 110 degrees, inlet ports 60 degrees, combustion chamber temperature etc

So where you place the sensor determines what temperature you are likely to see.

cheers

<{POST_SNAPBACK}>

This is why they invented water injection pre-turbo to lower all the combustion chamber temps... by over 35%

[Roy]

...no thanks...may work great, but water isnt that compressible last time i checked, andi dont have that much faith in control systems, be it the car tuned for it and then you run out of water...or a problem means one day you start your car and BANG bent rods

[s13rb26]

...no thanks...may work great, but watter isnt that compressible last time i checked, andi dont have that much faith in control systems, be it the car tuned for it and then you run out of water...or a problem means one day you start your car and BANG bent rods

<{POST_SNAPBACK}>

*cough*mechanical water injeciton*cough* dont buy cheap china stuff that runs off electronic components.

[CRSRB25DE]

Using your (probe?) placed somewhere on the cylinder head casting will give you a fair idea on whats happening.

I dont think water injection is used to cool down the cylinder head as much as cooling the intake charge.

I see cyl heads on an almost daily basis that have overheated and have gone soft. (i usualy ditch the head any where under 65 brinell)

Good idea to have an alarm at a certain temperature!

[Roy]

LOL...but whats a certain temperature? Does anyone knwo what temp they het heads to when they are pressure testing them?

[CRSRB25DE]

I only heat the heads around 80-90 celcius when pressure testing.

The only time i pressure test hot is if the customer has a water prob and we cant find it and/or the head has been welded etc.

Why dont you keep an eye on the temps and watch for any changes?

Make sure you tell us some details.

[Roy]

Ok, i suppose i can see how the head temp changes in conjunction with coolant temps. Dont know if that will tell me about engine stress though...maybe its a bad idea and i shoudl just buy a radiator

[rob82]

THe xr6t's have a cylinder head temp sensor right in the middle between the two valves on the back of the head no 6 cylinder. At 300rwkw a 10 second dyno ramp can yeild a rise temperature from around 90deg to 110-115 degrees. I would have though at this temp the coolant would start to boil?

[discopotato03]

Hi Roy , some years ago Craig Allen from Allen Engineering in Mallala said they were using multiple coolant temp probes along the head of an RB30ET . This was done because when souped up the head was suffering localised overheating I think down the back and some plumbing alterations were used to get more even water flow and temperature along the length of its head .

Most engines probably use water temp probes at the front or where the water outlet to the radiator is . Doing it this way should be ok but when power output is pumped up its difficult to know whats going on at the other end of the heads water jacket . Craig said something along the lines of 86deg at the front of the VLT head and 110 down the back .

I think major dramas occur when there's localised boiling and steam pockets form in the jacket , where there's no water there's no cooling so localised thermal overload can cook/warp/crack the casting . I have seen examples of heads that have small water lines tapped into high points in the jacket to give any bubbles an escape path usually to a header tank which is the highest point in the cooling system .

Any way I suppose another water temp probe down the back of your engines cylinder head would tell you if the coolant temp was even along its length .

An exhaust temp probe between the head and turbo would be handy because if the temp got out of hand something may fail before the water temp gauge could tell you particularly if your racing and need all attention on driving the thing .

The rally people tend to use a bright dash light and loud buzzer to warn them of

imminent doom ie for oil pressure/water temp or whatever they choose to hook up .

I think there is available head temperature probes for air cooled engines such as Dak Daks (VW's!) but I'm not sure if it would tell you anything useful on a water cooled engine . Either Allen Engineering or Nizpro have used a temp probe under spark plug type washer but not sure if its purpose was head or exhaust gas temperature .

Gary is there any specific issues with the RB twin cam heads and water cooling ?

Cheers A .

[blind_elk]

...110-115 degrees.  I would have though at this temp the coolant would start to boil?

<{POST_SNAPBACK}>

The water doesn't boil for 2 reasons:

1. It's under pressure - pressure affects the boiling point of water. On top of Mt Everest you can't have HOT coffee because the boiling point of the water is so reduced by the low atmospheric pressure. Inversely, higher pressures RAISE the boiling point.

2. The "coolant" chemically modifies the water so it boils at a higher temperature. For the same reason, they spread salt on icy roads because the salt lowers the freezing point of water.

Basically this is why you NEVER remove the radiator cap from a hot engine - the water is likley to go "super-heated", and suddenly turn to steam.

[Roy]

I have pictures of an NA race RB20, and it has a big ass coolant lien at rhe back of the head, mush like you see at the front of the head/plenum???? mayeb they had worked out a cure for the temp differential? Or is that i have never paid enough attention in noticing this line on other RB engines before?

[MattSR]

Roy, can you post the cpics please?

Also, have a look at any of the JUN modified RB26's (especiallty GTR-700) this will give you some ideas on cooling system mods

[MattSR]

Like this

[MattSR]

And here is the specific point on the cylinder head that the three coolant lines are taken from - one between 1 & 2, another between 3 & 4 and another between 5 & 6.

[Ronin 09]

don't think this answers your question, but was talking to a race engineer and he said that they don't worry too much if there is a ~20 degree difference between water and oil... even up to 120degC on water... they run alloy heads too but I guess temp control across the head front to rear may be the key (ie. maintained temp across the head)?

[Sydneykid]

Like this

<{POST_SNAPBACK}>

All that system does is make sure that there is no air trapped in the engine. All the water lines feed upwards to for areas where localised trapped air is possible. Does NOTHING for improved water circulation.

cheers

[Roy]

Oh forgot to post the pics...