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#4498826 - 08/26/17 04:53 PM Surface of intake manifold temperature
wrcsixeight Offline


Registered: 10/15/10
Posts: 1731
Loc: california
My OEm coolant temp gauge was reading outside what i was used to seeing, reading higher most of the time, yet my mechanical OP gauge indicated the oil temps were normal. I recently replaced the 6 year old 2 1/8" Motorad 195 thermostat with a Stant Superstat 195.

Wanting more data, I used thermally conductive epoxy to adhere a K type thermocouple to my intake manifold and covered it with a few layers of gaffer's tape.

This indicated that level driving at freeway speeds the manifold surface was basically 172 to 185, and only really went above that after slowinng down for traffic lights, or when climbing extended grades. The OEM gauge swung more wildly and often I would see the OEM gauge level then turn on the digital display and my guess as to the reading, often be off by 10 degrees or more, even after doing this for ~2500 miles in 6 days of observations.



The Highest temp I saw on Thermocouple on manifold was 208.3 F, and that was climbing the Grapevine Southbound on I-5 where one goes from ~300 foot elevation to 4500 feet in just a few miles. Ambient temps was ~95f. The OEM gauge rose pretty high too. I was only able to maintain 50MPH in third up this grade with my foot nearly to the floor.

Anybody else ever collect temperature data on the surface of the engine and or have any comments as to how closely the temperature of the coolant relates to the surface of the engine?

I think I need to cover the several layers of gaffers tape with some reflective tape to better insulate the thermocouple from air passing over the engine.
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#4498837 - 08/26/17 05:15 PM Re: Surface of intake manifold temperature [Re: wrcsixeight]
bsmithwins Offline


Registered: 06/24/09
Posts: 362
Loc: OR, USA
I have a code reader plugged into the diagnostics port of my Subaru (FB20 motor, naturally aspirated), mostly for using as gauges. Just for fun, I usually have it set to reading voltage, manifold absolute pressure, coolant temp, and intake manifold temp.

The intake manifold temp is very variable and is frequently 80-100 degrees F hotter than ambient, and that's w/o pulling a load up an incline. I'm not surprised by your readings, although I would have been before I bought the code reader.

BSW

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#4498884 - 08/26/17 06:40 PM Re: Surface of intake manifold temperature [Re: wrcsixeight]
69GTX Offline


Registered: 09/23/15
Posts: 3815
Loc: Connecticut
I've collected "data" and know that around the 180-190 deg F range you can't leave your hand there at all. Down around 165 deg F a brief touch. My pair of intakes always allow me to leave my hand there after a summer ride. So I don't think they run higher than 125-145 deg F with no external loads on the cars. The intake composition (metal or composite) can make a big difference too. A too hot intake is related to a hot running engine. Been there and done that with some 1960's muscle cars with cast iron and aluminum intakes.
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#4498911 - 08/26/17 07:31 PM Re: Surface of intake manifold temperature [Re: bsmithwins]
CR94 Offline


Registered: 03/20/16
Posts: 1120
Loc: Western S.C. since 1996
Originally Posted By: bsmithwins
... The intake manifold temp is very variable and is frequently 80-100 degrees F hotter than ambient, and that's w/o pulling a load up an incline. ...
Is that the intake air temperature as reported through OBDII system, or the external surface of the manifold?

I see intake air temperature roughly 10-20F above ambient, normally.
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#4498926 - 08/26/17 07:51 PM Re: Surface of intake manifold temperature [Re: wrcsixeight]
eljefino Offline


Registered: 06/15/03
Posts: 32640
Loc: ME
I did something similar. Put together a mongrel saturn motor.

Chassis was a 95 and the cylinder head was about a 97. Chassis gauge had its own sender but the engine was designed with "one less hole" to coolant, and the computer drove the gauge. No matter! I removed a bolt for a lifting hook and just jammed the gauge sensor in there. This was the outside of the aluminum cylinder head on a corner. Gauge read hot when I gave 'er the beans going up hills and stuff but otherwise mirrored coolant temp. I verified via scan-tool that the engine was running thermostat temp and all was well.

My theory is that increased heat in the head also means increased coolant flow, but the corner I was measuring was far from any water jackets.

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#4498958 - 08/26/17 08:38 PM Re: Surface of intake manifold temperature [Re: wrcsixeight]
IndyIan Offline


Registered: 09/23/08
Posts: 9092
Loc: Ontario, Canada
Your intake manifold is sucking in ambient air, so I found intake air temperature(reported from the ecu) actually gets cooler at WO throttle, especially with plastic intake manifolds, but none of my cars put coolant through the manifold.
I would guess that you should really find another place for the thermocouple, maybe right in the rad where the coolant enters would probably give you the best readings.
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#4498974 - 08/26/17 09:08 PM Re: Surface of intake manifold temperature [Re: CR94]
bsmithwins Offline


Registered: 06/24/09
Posts: 362
Loc: OR, USA
Originally Posted By: CR94
Originally Posted By: bsmithwins
... The intake manifold temp is very variable and is frequently 80-100 degrees F hotter than ambient, and that's w/o pulling a load up an incline. ...
Is that the intake air temperature as reported through OBDII system, or the external surface of the manifold?

I see intake air temperature roughly 10-20F above ambient, normally.


Temps reported via the ODBII.

BSW

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#4499078 - 08/27/17 12:35 AM Re: Surface of intake manifold temperature [Re: IndyIan]
wrcsixeight Offline


Registered: 10/15/10
Posts: 1731
Loc: california
Originally Posted By: IndyIan

I would guess that you should really find another place for the thermocouple, maybe right in the rad where the coolant enters would probably give you the best readings.


I could put another thermocouple on the radiator inlet, my unit can read 4 inputs at once. i have one on my alternator, voltage regulator, battery.

My Intake manifold does have coolant running through it. I just saw it go over 200F idling in a drive through, before my thermostat opened all the way and it began to cool back down and settled at 193, until i started moving again and then went to the low 180s. It does not really jibe with my OEM temp gauge though. A delay is expected, my my expectations including delay are not what I expected to see.

Mostly I am satisfied that it is not running too hot, as the OEM gauge would have me believing, sometimes.

But higher speeds and more airflow underhood does lower its reading.

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