Cylinder Head Temperature Sensor??

Gannon · Post by **Gannon** » Fri Apr 25, 2008 7:50 am

I have heard of a few stories where radiator hoses have blown, pumping out all the coolant and overheating the engine because it didnt register on the temp gauge through lack of coolant at the thermostat.

Which got me thinking.....

Why not mount a temp sensor or switch on the cylinder head (which is where the most damage occurs in an overheat, ie. headgasket or exhaust port/water-jacket crack) to warn when the cylinder head reaches a dangerous temperature?

After a bit of research, i found that some cars utilise CHTS (mostly air cooled engines like Porsche and VW)

I can see two ways of doing it...
1. Mount the factory temp sender to the head (as opposed to the thermostat) and connect it to the factory temp gauge on the dash
2. Use a thermocouple and a digital display to have an accurate display of CHT, here is an example of a thermocouple that installs between spark plug and head

Opinions anyone?

discopotato03 · Post by **discopotato03** » Fri Apr 25, 2008 8:44 am

Gannon Ford used to have a sensor gadget that sensed if no coolant was present ie the engine lost its coolant for whatever reason .
I suppose if you had something like this grafted in it could tell you if the coolant level had dropped suddenly .

With air cooled engines like Porsche and dak daks mixture control is critical to head casting temps so their engine management systems have to know to compensate if they are getting too hot .

I think the golden rule with Subaru or any cooling system is to change hoses long before they get the chance to let you down . Same with elderly plastic tank radiators - cheaper in the long run .

A .

steptoe · Post by **steptoe** » Fri Apr 25, 2008 9:02 am

I was thinking pressure sensor some time back. If the standard OPERATING pressure is about ya 13 to 15 psi , if ya could incorporate a buzzer to buzz once operating temp has been reach and pressure drops. We don't want a buzzer goin' off until op temp. Simple oil pressure switch that earths out at say 6psi to say "Bud, your water pressure has dropped"

Gannon · Post by **Gannon** » Fri Apr 25, 2008 9:29 am

Those are fair points, but i still wanna try it.

Do you think there could be any negative consequences to moving the temp gauge to the head?

Ben · Post by **Ben** » Fri Apr 25, 2008 11:37 am

Gannon, just go the k type and panel meter gauge idea and leave the temp sensor in the rad.

Subafury · Post by **Subafury** » Fri Apr 25, 2008 11:38 am

why dont you just put another sender unit in there and hook it up to an aftermarket gauge- bout $30-$40 for it and gauge comes with everything, except how to mount sender.

Matatak · Post by **Matatak** » Fri Apr 25, 2008 12:56 pm

i wouldnt be moving the factory sender at all.

but i do like my new one which is in the line of the Top Rad Hose. works well and tells me pretty accurate temps

discopotato03 · Post by **discopotato03** » Fri Apr 25, 2008 1:53 pm

Matatak the problem with taking readings beyond the thermostat is that it relies on it being open .

I think your going to find that the coolant temperature won't be significantly higher in the heads than it will be in the "log" behind the inlet manifold . Hot water is less dense than cooler water so its lighter and rises to the highest point it can reach . This water log is the highest point before the thermostat's well and that's why Subaru place the gauge temp sender at this point .
If the system is losing coolant slowly the level drops from the highest point which in a L/MY is the top of the radiators tanks (2 in a cross flow rad) .
The cooling system pressure may not necessarily drop so pressure is not a 100% reliable method of measuring its health .

The important things to know are that firstly the cooling system is full and that the water temperature is not too high .

From an interest point of view there's no reason why you couldn't place two more temp senders at either end of the water log (I can't see any advantage of having the in the head castings) and from this you could learn the temperature of the water rising up through each individual head . Trouble is I doubt you could change anything about the system if you didn't like it .

When I was concerned about coolant temps last summer I bough a digital infra red thermometer from Jaycar - Digitech QM 7223 so that when I played about with different temp thermostats I could see what was going on .
It's a great tool because you can point it at anything and get an instant read out to a tenth of a degree centigrade . I had it all over Ellies EA82T engine to monitor warm up and running temps . Believe it or not cooling system wise my engine runs a uniform temperature as in whats coming out of either head is the same temp as the thermostat well , even water return from the turbocharger shows the same reading . What you can see changing is the temperature as the engine heats up and after the manually set thermofan pulls more air and things cool down again .
Can point it at tyres , brake discs , turbine housings and even your coffee cup .

I think the Ford sensor is the go if your worried about sudden coolant loss and a cooked engine . I think it has two pins exposed to the coolant and runs a low current between them . Logically if the coolant level falls below the level of these pins the circuit is broken and it sends you are warning ie idiot light or buzzer - whatever you hook it up to . You would place it as high up in the cooling system as possible to give you the earliest warning .

I'll see what I can find out about the sensor later , cheers A .

Gannon · Post by **Gannon** » Fri Apr 25, 2008 7:57 pm

Ah so you've had a thermo gun on the Ea82T

What im really curious about is how much the head heats up when you boot it.

My other queery is, what would be the max head temp you would wanna run? 100degC?

If i put a thermoswitch on the head to warn me of overheating head, it might just save me from a blown headgasket

discopotato03 · Post by **discopotato03** » Fri Apr 25, 2008 10:07 pm

Gannon provided the coolant temp was even throughout the cooling system and there was no localised boiling causing gas pockets I think a healthy L/EA82 could survive short periods at 100C .
It would be better if it had a higher pressure rated radiator cap because waters boiling point rises at elevated pressures .
The aftermarket ie Nismo/HKS etc often do higher pressure caps for apps where the coolant temp is expected to be greater than normal .

Engineers don't look at temperature like most people do ie freezing and boiling point of water 0-100c , they look at absolute temperature and pressure as well .

The things that generally cause high head temperatures are high combustion and therefore high exhaust gas temps - assuming the engine and all its support systems ie cooling system are in good condition .
If for whatever reason they get hot the usual give away is higher water temps and at times detonation .

Engines die when they lose their coolant quickly because some parts of the head and block castings run hotter than others and so they twist and warp out of shape . The blocks and heads decks don't stay flat/square /parallel for long because of uneven thermally generated stresses so usually the head gaskets break the fire ring seal between the head and block and combustion pressure escapes often into the cooling water jackets .
Now because combustion pressure is heaps higher than cooling system pressure the invading super heated gasses overwhelm the cooling systems ability to cool its water . These gasses can form the bubbles you can see if you look into the radiator of a running engine with a damaged head gasket .
If the leak is big the combustion pressure being the greatest forces the rad cap to open and theses gasses literally blow the coolant past the cap into the overflow and beyond .

These cars being the age that they are (L/MY) will suffer eventually purely because of wear and tear .
I think all you can hope to do is replace everything that you practically can ie hoses/thermostat/water pump/radiator/belts if the car has an unknown history .
If you didn't mind spending the money reconditioning the heads - meaning a slight 3 thou skim off their decks and new factory gaskets - then this is about the best chance there is of avoiding gasket sealing problems .

Cheers A .

Matatak · Post by **Matatak** » Sat Apr 26, 2008 4:37 pm

discopotato03 wrote:Matatak the problem with taking readings beyond the thermostat is that it relies on it being open .

The EJ thermostats are in the path of the bottom hose. so the top hose shall warm up as the engine warms up.

so my temp guage reads fine as the Bottom hose is the one which is cold until the thermostat opens unlike the EA's.

discopotato03 · Post by **discopotato03** » Sat Apr 26, 2008 11:00 pm

In that case yes but EA81/82 have them just short of the lower end of the top rad hose .

D3V1L · Post by **D3V1L** » Sat Apr 26, 2008 11:09 pm

ive been told that one or two old french or something cars have temp sensers in the heads rather then the thermostat..i cant remember what but ill try finding my info and get back to ya..there was a reason behind it as wel but cant remember for the life of me

dave

steptoe · Post by **steptoe** » Mon Apr 28, 2008 2:06 pm

and look forward to the buggers having French threads too, maybe?

Gannon · Post by **Gannon** » Mon Apr 28, 2008 5:50 pm

Were they air cooled French cars?

French threads would be metric wouldn't they?

Im still interested in getting a temp gauge and testing different parts of the engine. Maybe one temp gauge with several sensors and a switch to select say, coolant temp, head temp, pre and post intercooler temp and maybe even exhaust temp