Diesel engine temperature

Submitted: Monday, Sep 10, 2012 at 21:47
ThreadID: 97950 Views:17922 Replies:6 FollowUps:5
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Does anyone KNOW for sure the normal operating temperature of a 1HZ diesel?
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Reply By: Member - Walter H (WA) - Monday, Sep 10, 2012 at 22:08

Monday, Sep 10, 2012 at 22:08
G'day Whirlwinder,I installed a engine "Watchdog" to my 1HZ after fitting a Turbo/Intercooler and when the Toyota Gauge is a dash over the half way mark my engine watchdog reads 85 c and this is when the temp is around the mid 30's,but when im out in the desert's in the middle of the year and day time temps are around 18-20 the watchdog reads around 65 c, but the sensor on the watchdog only picks up the metal temp as its fitted under the head bolt at the rear of the rocker cover which is how they have been designed to eliminate having to make any penetration's in the cooling system....Hope this helps
AnswerID: 494667

Follow Up By: fisho64 - Tuesday, Sep 11, 2012 at 00:12

Tuesday, Sep 11, 2012 at 00:12
its fitted under the head bolt?
sorry to say, but I would not remove a head bolt to put the sensor underneath? In fact you really shouldnt remove one bolt without re-torqueing the whole head with a new gasket?
I have a similar unit (engine guardian) and it goes under one of the bracket bolts near the water outlet.
FollowupID: 770310

Follow Up By: Member - Walter H (WA) - Tuesday, Sep 11, 2012 at 09:18

Tuesday, Sep 11, 2012 at 09:18
There is more then one type of bolt in a head eg; Lifting bracket bolt that has nothing to do with holding the head to the block which is only 25mm long and runs parallel with head up near the fire wall beside the rear core plug.Forgive me for not being more specific !
FollowupID: 770319

Follow Up By: fisho64 - Tuesday, Sep 11, 2012 at 09:50

Tuesday, Sep 11, 2012 at 09:50
Your forgiven-this time but dont let it happen again :-)
FollowupID: 770329

Reply By: Ross M - Monday, Sep 10, 2012 at 23:02

Monday, Sep 10, 2012 at 23:02
The normal operating temp is set by the thermostat and it opens more when more heat value is being made and shuts a bit when less heat value is given to the water. Most thermostats are around 82 degree C and that is where the engine water temp leaving the engine should run if everything is normal.
What is normal though? We drive in many different situations which taxes the cooling system more and sometimes less, so normal varies above and below the 82C
On a HOT day the heat may not be able to be dissipated so easily and the thremosat will be fully open trying to pass as much water to the radiator for cooling. If the rad can't get rid of the heat then the engine water temp will go higher than normal. May get to 100C but it shouldn't boil at that temp because of the pressurization of the system.

The temp Dog system bolted to the engine heat indictates the metal temp at the external faces of the engine and will be a bit less than the actual water temp leaving the engine. These systems are good because they indicate if there is no water unlike the OE gauge which stop reading with loss of coolant.

A coolant level indicator is a great device to have as it saves the engine if there is not enough coolant.
AnswerID: 494668

Reply By: Dust-Devil - Tuesday, Sep 11, 2012 at 11:17

Tuesday, Sep 11, 2012 at 11:17
Morning Whirlwinder.


I have a 1997 1HZ Troopy which I bought bog stock standard from Fowles Auctions, Melb in 2000. It was previously owned by the Vic Govt and used as an instrument vehicle by the NRE dept. 30,000km on the clock.

Since purchase of same I have custom modified it extensively over the ensuing years which has included two (2) turbo's, LPG gas injection, 4-5 different suspensions, pop-top camper conversion etc etc plus a whole load of other R & D 'playing arounds'. This has resulted in a 3Tonne vehicle - GVM upgraded to 3.5T.

In addition to the above I have flogged, abused, bashed & trashed that vehicle unmercifully, which on one occasion resulted in the front end being shifted 6in to the rear and the front diff bent like a banana.

I also on occasion had the OEM Temp Gauge zoom up to the red mark.

Punchline being: regardless of what I did to that vehicle, it never broke to the extent that it never got me home.

As I became more knowledgeable & experienced about diesels, I added some after market monitoring gauges such as an EGT (post first turbo) which gave me an instant heart attack when I saw what I had been doing to the engine and a couple of Engine Watchdog TM2 gauges.

One of the TM2 gauges was connected to the water outlet housing on the head and to the Water inlet housing on the side of the block.

YES! one gauge monitoring two points via a DPDT centre off switch. This gives me as close as possible the coolant temp exiting the head and entering the engine post radiator.

The TM2 gauge is used to monitor front and rear diff temps which is another story all together.

On installation the TM2 monitoring the coolant temps showed 80C exiting the head and 72C entering the engine. I.E. the radiator was dropping the temp by 8C on a pass through. I questioned a number of mechanics re this (8C diff) and was advised - all good, thermostat going its job.



Over the last 12months I became aware that the vehicle in question was losing coolant and guessed a head gasket??????? Took it down to the guy I now use for everything and to cut a long story short it resulted in the following:

Head: 4 large cracks, one in ea of cyl 2,3,4,5.

Radiator: 75-80% blocked.

Fixes: (1) New head incl valve guides, Stellite Valves and matching seats.
(2) OME Radiator - plastic tanks removed, rodded and resealed

I queried the radiator reconditioning and was ensured that these days there is not an issue with this process and all is good. Even though I have great faith in this mechanic, I am still not 100% convinced and only time will tell.


Vehicle now runs temps as follows 60kph:

78C on Head outlet

56 - 58C on engine inlet

Takes quite a awhile to reach these temps.

At 100kph on freeway it runs 80C on Head outlet to Radiator and 60C on Engine inlet.

I have not tested it towing under load or in the warmer months of summer which are to come. However, I have no doubt all of these factors will give varying temps.

Reasons given by 'experts' for head cracking.

(1) Blocked radiator

(2) LPG gas injection

(3) No monitoring gauges in early years to monitor what the engine was being subjected to. This resulted in gross over fueling leading to over heating which was not indicated by OEM Tempo gauge until too late.

On changing turbo's 4 years ago I removed the LPG injection system.

I have no complaints about this 1HZ as the above reported problems were all self induced by my penchant for R & D tinkering, unknowingly (lack of monitoring gauges) abusing the engine etc etc.

I do not anticipate any further similar problems.

Whirlwinder, I hope this answers your question and gives you a few extra ideas re your 1HZ.

One other thing- always use Toyota red coolant as it is a totally diff mix than other coolants. Also it is approx same cost.



AnswerID: 494685

Follow Up By: Dust-Devil - Tuesday, Sep 11, 2012 at 11:19

Tuesday, Sep 11, 2012 at 11:19

As mentioned above by some one. The thermostat is marked as opening at 82C.
FollowupID: 770334

Reply By: Whirlwinder - Tuesday, Sep 11, 2012 at 15:22

Tuesday, Sep 11, 2012 at 15:22
Thanks for the replies. They confirmed what I was thinking.
AnswerID: 494699

Reply By: Member - poppygrumps1 - Wednesday, Sep 12, 2012 at 09:43

Wednesday, Sep 12, 2012 at 09:43
I just replaced my thermostat with one from Toyota which is marked 76 C .
I also have a watchdog which I used to have connected to the bolt of thermostat housing and the reading was 77 C on normal running and never going above 88 C in around 12 months. I have now have gauge connected to the housing for the top radiator hose and have reading of 81 C and have had it up to 91 C flogging it up a long hill.
AnswerID: 494755

Reply By: Member - Phil G (SA) - Saturday, Sep 15, 2012 at 18:59

Saturday, Sep 15, 2012 at 18:59
1Hz thermostat opens at 76 degrees and is fully open at 95 degrees.
Engine watchdog temps measured on the alloy water outlet bolt are usually 76-80degrees when the cooling system is in good nick.
AnswerID: 494971

Follow Up By: Whirlwinder - Saturday, Sep 15, 2012 at 21:48

Saturday, Sep 15, 2012 at 21:48
Thanks guys for that info. Mine has reached 75 deg but the ambient temp has been just 24 max so I have set the alarm at 80deg so far but will adjust as I "learn".
FollowupID: 770654

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