anyone using Engine Watchdog or similar for temperature check

Submitted: Thursday, Apr 10, 2014 at 21:11
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Hi everyone. What variance in engine temperature do you experience with differing conditions?

For example, Highway travel unloaded, Towing, Differing Ambient temperatures, Stopping at roadworks after highway cruising, Towing caravan or trailer up steep dirt track in 1st gear, Stopping at traffic lights.

I assume that there will be differences in engine temps under different conditions but I wonder how much and why.

Thanks in advance

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Reply By: Member - Rosco from way back - Friday, Apr 11, 2014 at 07:51

Friday, Apr 11, 2014 at 07:51
I wouldn't expect it to change all that dramatically Cruiser.
The engines are designed to run in a reasonably narrow temperature band (maybe around 104-107 deg C). So if they have to work harder in situations as you describe, the fan cuts in and out to maintain the temp, as does the thermostat.

I know temp gauges aren't all that exacting, but you don't usually see much change with them.
AnswerID: 530281

Follow Up By: cruiser 3 - Friday, Apr 11, 2014 at 09:39

Friday, Apr 11, 2014 at 09:39
Thanks Rosco for taking the time to reply, you may be interested in the replies from others who show that what happens practically is sometimes quite different to therory.
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Follow Up By: Member - Rosco from way back - Friday, Apr 11, 2014 at 10:06

Friday, Apr 11, 2014 at 10:06
Certainly interesting Cruiser. The whole point in having a pressurised system is to raise the boiling point above 100 deg.
From the postings it would appear this to be unnecessary which I find surprising, given that philosophy is applied across the board.
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Follow Up By: cruiser 3 - Friday, Apr 11, 2014 at 10:30

Friday, Apr 11, 2014 at 10:30
Hi Rosco
Yes I am finding all the replies very interesting and appreciate the feedback.

I believe with a 15 psi radiator cap and 50/50 mixture of Ethylene Glycol the boiling point is raised to 130deg, so we all have a lot in reserve.

Engine Watchdog or similar is a great way to monitor our cooling system however I find I become a little bit obsessed and worry uneccessarily sometimes while on a trip when I see a rise in temp.
This post is an attempt to learn more from others and find reassurance that all is well with my system.

Ideally if manufactures could design a cooling system that maintained a constant temperature motors would last even longer than they do but I think this is impossible
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Follow Up By: The Bantam - Friday, Apr 11, 2014 at 22:51

Friday, Apr 11, 2014 at 22:51
The actual block temperature of most vehicles in good health should vary very little once warmed up, until it gets to the point where the cooling system is not keeping up then the temperature will rise.

Our cooling systems DO self regulate by a couple of means.

The use or presurisation and addition of glycol does most definitely increase the boiling point of the coolant......many modern cars will boil their little heads off with very little provocation if the correct amount of coolant is not used.....Most modern cooling systems run fairly hot..normally.....many cars especially toyotas run a pretty stiff concentration of glycol in the coolant.

The first self regulation mechanism is the increased boiling allows the radiator to run a a much higher temperature in comparison to the surrounding air.
As the temperature of the radiator increases, the temperature gradient to the surrounding air increases making the cooling system more efficient.......thus a tendancy to stabilise the temperature.

Even the heat variance within the radiator effects the cooling efficiency......the radiator is not always all hot......there are times when the bottom of the radiator may be quite cool while the top can be at operating temperature...thus the radiator varies in efficiency...the top will be transfering heat very much more effectivly than the bottom.

The second mechanism for temperature regulation is the thermostat...many people are under the misconception that the thermostat is either open or closed and once it opens it stays open.
This is not true, the thermostst is constsntly opening & closing and varying its opening regulating coolant flow from the radiator to the block.

The third mechanism is the fan...most modern cars have some sort of temperature variant fan, be it an electrick fan with a temperature switch or a viscous hub mechanical fan the varies its drive coupling with temperature.

Without exception pasenger car radiators have limitations and are not capable of dealing with full engine output for extended peroiods.

Once the temperature has risen above normal, that is a sign the the cooling system is not keeping up...if the engine continues to produce the same amount of power under the same curcumstances it will eventually overheat.

A clasic example of this is burn out competitions........vehicles put in a situation where they are constantly producing maximum power, with poor airflow......If the engine and transmission hold there are two ling the rubber lasts and how long till the radiator boils.....neither are very long.

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Follow Up By: Member - Rosco from way back - Friday, Apr 11, 2014 at 23:25

Friday, Apr 11, 2014 at 23:25
Yep .... what Bantam says so eloquently is more or less what I said in a couple of lines.
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Follow Up By: cruiser 3 - Saturday, Apr 12, 2014 at 09:17

Saturday, Apr 12, 2014 at 09:17
Hi Bantam and Rosco
You describe the function of a cooling system very well.
But do these mechanisms that regulate water temp maintain a constant temperature?
I think if a vehicle was working at a constant speed and load then yes the engine temp would be constant.
But when variables like changing speed and load and in particular reducing air flow through radiator are introduced then I don't think the system can respond quick enough to maintain exact engine temp.
An extreme example is when travelling at highway speed, the thermostat is probably only partly open and maximum airflow is going through radiator with an engine temp probably 85deg. Then come to a sudden stop and idle at roadworks for 5 minutes.
Now there is very little air flow through radiatot because viscous fan varies with engine speed and the water pump is pumping a lot less water, the thermostat must open immediately to compensate. Would this not cause a variance in temperature while the cooling system "catches up"
For your consideration
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Follow Up By: The Bantam - Saturday, Apr 12, 2014 at 09:40

Saturday, Apr 12, 2014 at 09:40
If you think any part of the engine is at a constant temperature, you are never will be.

But considering the operating range of the coolant is well below zero to well abover 120C....10 or 20 degrees is neither here nor there.

The cooling system efficiency will continue to increase right up to the boiling point of the coolant or the venting pressure of the radiator , due to the increased temperature gradient to the oustide world.

As soon as the cooling system boils or vents, system efficiency drops considerably.

What we need to know the coolant temperature increasing above normal...if so the cooling system is not keeping up.

If the coolant temperature continues to increase you have a problem......and not soon........have had for a while.

most vehicles will sustain coolant temperatures moderatly above "normal" and below venting indefinitely as long as heat in is less than heat out.
But that comes down to knowing your vehicle and how far you can push it.

As for setting an alarm for a particular coolant temp.........BEEP BEEP BEEP.........mate you had a problem 5 or 10 minutes you have a real problem.
Set it too low and it will be nothing but a neusance, set it too high and well its pretty pointless...above all remember coolant temperature lags heat generated and heat disipated by quite a bit.

I can see a role for coolant temperature allarms on engines that are not actively operated or attended.

But in a car or should have known you had an issue long before the allarm tells you.

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Follow Up By: cruiser 3 - Saturday, Apr 12, 2014 at 09:55

Saturday, Apr 12, 2014 at 09:55
That's exactly my point, temperatures do vary. I guess that is proved by the thermostat spec being; starts to open at 82 fully open at 95 showing that engine temp should be controlled within that range
Anyway I am happy that my engine and cooling system is working fine but these replies have been very informative,
FollowupID: 813290

Follow Up By: The Bantam - Saturday, Apr 12, 2014 at 10:37

Saturday, Apr 12, 2014 at 10:37
Being informative is what these forums should be all about.

A far exchange of information & ideas.

I think the reasonable range is a bit outside the thermostst range...but by the time all the regulating factors come into operation the normal window of a cooling system is pretty damn narrow and well regulated considering.

And remember all these regulating mechanisms are good old 40's & 50's phsyics & mechanics.

We have seen a few new fangled things like electric thermo fans & electric water pumps...but the majority of cars & trucks run cooling systems pretty much as you could have seen them in the post war period.

FollowupID: 813293

Reply By: Erad - Friday, Apr 11, 2014 at 08:52

Friday, Apr 11, 2014 at 08:52
I have had an engine watchdog for a long time now. It was initially installed on my NL Pajero. This was a V6 engine, running mainly on LPG. The recommendation was to mount the temperature sensor on the thermostat housing, and this is what I would normally do. In the case of the Pajero, the thermostat housing was well away from the heads or engine block, and I was worried that if I lost water suddenly (a blown welsh plug or hose), there would be no water in the housing to get hot and bring up the alarm. The next accessible place was a bolt on the intake manifold, which was where I mounted the sensor.

The unit displayed the temperature of the intake manifold, and therefore was subject to variations in the ambient air temperature, but it was mounted close to the heads (which is where I wanted to monitor). When the engine was up to operating temperature, but with ambient temps sub-zero, the unit displayed temps about 30 Deg C. On days of 30 + Deg C, it displayed around 80 Deg C. Travelling on the open road, I could always tell when the radiator fan coupling cut in - the unit displayed 83 Deg C. Most of the time, even up to 34 Deg C, the fan did not cut in at 100 km'hr, but as soon as I slowed down to 60 or less (in towns), the temp went up to 83 or 84 Deg C and the radiator fan cut in. Towing our caravan through Sydney traffic, the display used to get up to 90 Deg C when I had stop/start conditions . All this time, the temperature gauge needle moved less than the thickness of the pointer.

I had to set the alarm at 95 Deg C because of the heat sink effect. As soon as the engine was shut down, the display would rise and the alarm would scream (so did my wife!) It typically took maybe a minute after starting the engine to bring it back to below the alarm setting.

I now have a 2013 NW Pajero diesel, and the watchdog is fitted to the thermostat housing. The location where it is mounted is fairly shielded and the heat sink effect is still noticeable, although not as bad as with the old car.I also have a scangauge and one of the parameters I monitor is cooling water temperature. The scangauge shows the temps rapidly rising as the car goes up a hill, and then falling just as fast over the other side. The temperature displayed is 86 Deg C, and the maximum I have seen is 90, whilst towing my caravan in heavy Sydney traffic (ugh!). The thermostat settings for the engine are start to open at 85, and fully open at 90 Deg C. I use the scangauge as the mainmonitor, but also have the watchdog as a backup alarm.
AnswerID: 530283

Follow Up By: cruiser 3 - Friday, Apr 11, 2014 at 09:35

Friday, Apr 11, 2014 at 09:35
Thanks Erad, exactly the sort of information I was looking for.

best regards
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Reply By: Athol W1 - Friday, Apr 11, 2014 at 09:24

Friday, Apr 11, 2014 at 09:24
Cruiser 3
I have both Scangauge and Engine Watchdog fitted to my Toyota 200 TTD and I see big differences in the two temps. The Watchdog is fitted to the engine dip stick bolt on thee exhaust side of the right cylinder head and, depending on driving conditions, can read either lower or higher temps to the coolant temp on the Scangauge.

The largest difference was after towing my nearly 3 tonne van up Brown Mountain in southern NSW. This is a climb that required plenty of 1st gear work out of the corners so the car does work probably as hard as it ever would. The difference in temp was 93 coolant temp and 125 on the watchdog.

I chose this location for the watchdog as it would most probably be the area that gained temp the quickest should there be a sudden and catastrophic failure of the cooling system, and therefore the most likely early warning of this failure, as this area is the closest that I could reasonably access to the hottest parts of the engine (apart from the exhaust manifolds).

Never rely on the original manufacturers temp gauge as 1/ if you lose coolant the gauge will show cold (they only measure WATER temp) and 2/ they are deliberately designed NOT to show the temperature changes that do normally occur during different engine loadings and operation (in my Toyota there is no change to the original gauge reading between 60 and 95 deg coolant temp as shown on the Scangauge)

Hope this helps
AnswerID: 530290

Follow Up By: MEMBER - Darian, SA - Friday, Apr 11, 2014 at 09:31

Friday, Apr 11, 2014 at 09:31
Another example of that philosophy (not showing the driver the actual coolant temperature) went further for us with my wife's new Mazda CX5 - no temperature gauge at all ! - one is simply advised that the coolant is cold, or too hot.
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Follow Up By: cruiser 3 - Friday, Apr 11, 2014 at 09:42

Friday, Apr 11, 2014 at 09:42
Hi Athol
I bet you were glad that you had scan gauge as well otherwise seeing 125 on the watchdod would have been worrying.
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Follow Up By: Athol W1 - Friday, Apr 11, 2014 at 13:23

Friday, Apr 11, 2014 at 13:23
Cruiser 3
Yes, each system serves its own purpose. I also closely watch the auto trans temp with the scangauge, and keep the temp down as much as possible by prudent use of the gears.
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Reply By: MEMBER - Darian, SA - Friday, Apr 11, 2014 at 09:45

Friday, Apr 11, 2014 at 09:45
My watchdog sensor is bolted to the front of the head (on the side, behind a small shield). Fluctuations from easy driving to very hard working are probably in the range 78C - 88C at that point. I have the alarm threshhold set at low 90's I think - it always rises when the motor is turned off. But as mentioned above, I too think that the Toyota heavies have plenty of cooling capacity in reserve - I've towed across the Nullarbor in 42C at about 75-80kph and the cooling system was stable throughout, despite the air conditioning being on and having the bullbar/spotlights/winch obstructions in front of the radiator. Also as mentioned.... my factory temperature gauge too seems designed to stay mid zone, until a dramatic rise in coolant temperature occurs, so its a poor guide to fluctuations.
AnswerID: 530293

Follow Up By: cruiser 3 - Friday, Apr 11, 2014 at 10:17

Friday, Apr 11, 2014 at 10:17
Thanks for your reply Darian.
Like you I travelled the Nullabor towing a van and was told by the attendant at Balladonia servo that it was mid 40's. That was before Engine Watchdog was fitted but all was well.

it seems that a 10 deg varience is quite normal under conditions from normal to heavy loads.

My observations show some situations such as idling after highway running cause further increased temps (see my reply below)
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Reply By: cruiser 3 - Friday, Apr 11, 2014 at 10:06

Friday, Apr 11, 2014 at 10:06
To Athol and Erad.

your replies are appreciated. it shows that different locations show different reading but the main thing i think is we can monitor changes in temp.

My watchdog is fitted to an 80 series landcruiser and is located on the head near the outlet to the thermostat.

my cooling system spec are:
thermostat starts to open at 82 deg C fully open 95 deg
viscous fan fully engaged at 92 deg Radiator cap opens at between 110 and 120 deg

My watchdog shows the following:
normal running unloaded 80 to 85 Deg
Normally Towing van 86 to 88 deg (up to 91 during the heat of Darwin)
When stopped after a long run will increase to 99 deg (roadworks for instance)
Towing van up long steep track in 1st after highway travel 99 deg.

I assume from this and by info provided by you that these temps would be quite normal and indicate that:
the cooling system cannot respond fast enough to cope with changes in water pump speed, changes in airflow caused by stopping and thermost opening and closing.

my vehicle is in good working condition however i do need to add oil to the viscous fan from time to time. I have considered fitting an electric fan in front of the radiator to be used when low speed hill climbing and when stopping after a long run at lights or roadwork.

Any comments or further info will be appreciated.

Thanks again
AnswerID: 530295

Follow Up By: garrycol - Friday, Apr 11, 2014 at 11:03

Friday, Apr 11, 2014 at 11:03
These systems do not monitor water temp but the metal temp of the engine and water temp and metal temp may not have any correlation with each other.

I appreciate many instructions say mount the sensor on a thermostat bolt but I would advise not to do that as the metal in that area will be primarily influenced by water temp rather than engine block/head temps. Afterall you have the vehicle water temp gauge to advise water temp.

My advise is to have the sensor mounted to a bolt in the head or top of the block. Mine is mounted to a spare bolt on the lower head.

The temp from the Watchdog is not absolute temp but a reference temp to measure changes. For example my engine in normal operation has a water temp of 85-100 degrees. My watchdog has a temp of 72 degrees when the engine is operating normally and water temp is around 85-90. I have set my alarm at about 85 degrees. In normal driving the watchdog temp only moves from about 70 to 75 degrees while water temp can be all over the place. When stopped at traffic lights the watchdog temp can go up to about 80 as the head soak from the engine increases as there is less airflow over the engine when stopped.

On a hot day after I have parked and come back to the vehicle the the Watchdog temp alarm can go off because when stopped there is no removal of heat from the engine via the coolant or airflow over the engine so the heat soak builds up - shows how an engine seize when switched off when it has been overheated.

To set the watchdog up I get my engine to operating temp and then note the watchdog temp - then set the alarm at about 15 degrees hotter. Make sure then low coolant alarm works when the actual radiator get low and not just the overflow bottle. In some vehicles the main coolant system can drain if there is a hose failure but the remote filler bottle can still have coolant in it so if the low coolant sensor is there it may not set the alarm off.


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Reply By: cruiser 3 - Friday, Apr 11, 2014 at 13:05

Friday, Apr 11, 2014 at 13:05
Thanks Garry.
Your reply makes good sense.
It's interesting that everyone's situation is a little different in sensor location and temps recorded however to one thing in common is that temperatures do vary depending on driving conditions.
I would summarise what has been reported as a 10 deg change from easy to hard driving with a further possible increase of an extra 10 deg when when stopped or travelling at very low speed under heavy load
The info everyone is providing is very informative and confirms my idea of fitting an electric fan to help dissipitate heat when little air is passing through the radiator.
AnswerID: 530306

Reply By: The Bantam - Friday, Apr 11, 2014 at 23:21

Friday, Apr 11, 2014 at 23:21
The big issue with all temperature guages is.....what the hell you are measuring...and is that meaningfull.

The manufacturer guages are critisised for reading coolant temperature and relativly inaccuraltly.

But a badly located aftermarket temperature monitor can produce readings that are just meaningless and of no use at all.

The temperature of the engine varies all over the place..even the coolant can vary wildly from place to place.

in the lower parts of the engine and the radiator the temperatures may be considerably lower than the upper parts of the engine.

Even within the head the temperatures will vary.....right on top of the combustion chamber between the valves the head will be way hotter than over where the inlet manafold bolts are.

Realy there is quite some thaught and perhaps experimentation required to get a good location for a remperature sensor and thus some usefull readings.

There is a lot to be said for measuring coolant temperature.

AnswerID: 530364

Follow Up By: cruiser 3 - Saturday, Apr 12, 2014 at 08:18

Saturday, Apr 12, 2014 at 08:18
Thanks Bantam for your very informative replies.
I agree that my method of trying to monitor engine temp to avoid any problems is certainly not perfect but it is the best I can do.

I would like to fit a Scan gauge but I believe they are not compatible on a 1996 petrol Landcruiser, the diagnostic connector is rectangular and has irregular positioned pins.
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Follow Up By: The Bantam - Saturday, Apr 12, 2014 at 09:19

Saturday, Apr 12, 2014 at 09:19
I keep comming back to "what are you measuring and is that actually usefull"

The majority of pasenger car "temperature guages" are not marked with actual figures and are not calibrated with any sort of accuracy.

Generally the method of "measurement" is crude & fundamentally inaccurate in many ways....we realy have to ask ourselves is that realy a bad thing.

Consider that many of the modern vehicles retain the same old crude and inaccurate temperature guage system for driver viewing, but have several far more accurate temperature sensors for the purpose of engine managment.....we have to ask ourselves why.

The "temerature guage" realy should be called the "driver temperature indicator"....its role is to show that the general operating temperature of the engine is..."normal" or not.

Still most drivers do not know how to read a factory temperature guage..

These ..suposedly accurate temperature guages are sold on the basis of fear, uncertainty and doubt.

They tell us that we need to accurately know what the engine temperature is and that these guages can do that.

I believe wrong on both counts.

The major selling point is prevention of engine failure, due to critical coolant loss.

Realy if coolant loss is the issue, perhaps a coolant loss allarm would be more appropriate....but those can not be constructed cheaply & easily from pretty well off the shelf electronic parts and quickly bolted to the outside of the motor..

As can be found in heavy transport, earthmoving, high performance marine, critical task stationary engines and motorsport, if you want meaningfull temperature will not get them by mounting a sensor on the surface of the motor.

A coolant temperature sensor needs to be mounted where it is immersed in the coolant and in a meaningfull place....some high performance engines will have multiple coolant temperature sensors in well chosen places.

As for measuring block or head usefull is that.

What will save your bacon is......knowing how the cooling system behaves and learning to read a crude old temperature indicator.

Afterall, engine temperature is a slow changing variable, whatever temperature you are reading will significntly lag, in the order of minutes or at least tens of seconds the temperature where it matters.

If the temperature begins to rise above normal....the cooling system is already not keeping up.

As has been mentioned is very common for coolant temperatures to continue to rise after the load has been removed and the engine turned off....have seen in the past several times vehicles reading near normal temperatures pull up turn off and boil by the side of the road, minutes after pulling up.

Because the heat is still comming out of the block and the coling system is no longer working well.

If you realy want an accurate and meaningfull temperature guage, yoi want to be bolting INto the block and getting it into the water jacket..somewhere meaningfull.

FollowupID: 813284

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