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Discussion Starter · #1 ·
1998 Isuzu Rodeo S 3.2 4X4. The temperature gauge is reading hot. It may be hot, but I am not sure. The IR reads 170F on the upper hose. There is probably some variance for testing on the hose. It also reads 150 on the lower hose. About two years ago I replaced water pump.

The gauge has been reading three three lines below for right wide line. However, it has gone to the wide white line. It has gone beyond the wide white line. I would expect to see steam coming out of the cooling system if overheating, but I don't see any. Furthermore, I am able to take radiator cap off while testing at home after 15 or 30 minutes.

In past two weeks:
I changed single wire temperature sending unit for gauge from Auto Zone, then I replaced that one with O'reilly.
I changed coolant temperature sending unit two wire for computer.
I replaced fan clutch, and condenser fan.
I change antifreeze and radiator cap.

Afterwards still reading hot.

Checked compression 140 to 170 all cylinders
No antifreeze consumption
No exhaust bubbles in coolant
No water in oil cap
No visual overheating
No smoke from tail pipe
No rough idle
It has normal power

Codes: VSS and EGR. Changed both. Then no codes.

I replaced IAC solenoid.

Upper and lower radiator were getting hot with variance of 20 degrees. I saw fluid traveling in the radiator, so I was sure thermostat was opening and water pump was working and radiator was not clogged.

Just in case the thermostat was partially stuck closed, I changed it knowing it was a big job.

Thanks to Matt Payne's Intake Manifold video, I replaced the thermostat with Napa THM 376170, and I replaced intake manifold upper and lower gaskets. I replaced all the parts under intake manifold: hoses and knock sensor plus heater hose. Change throttle body gasket for maintenance.

I located OEM radiator for $99 on Ebay, and I replaced that too.
Afterwards still hot.

I double check the fan blade direction using Matt Payne's video, and it is the same.
I checked fan clutch and it engages, but I am not sure when it suppose to.

Where I am with this issue. I ordered a scan tool which will arrive Tuesday, so I can see coolant temperature according to OBD2.

I plan to purchase Isuzu OEM temperature sending unit.

I plan to perform a combustion leak test for Exhaust Fumes in the Antifreeze.

What I am hoping is that someone can tell me there is a known issue of some sort and what it is that would make the gauge read hot. Such as instrument panel, or using aftermarket sending unit. I hope for suggestion for a good combustion leak test to test for Exhaust Fumes in the Antifreeze.

I changed water pump two years ago, which was another big job. I am looking for a good reason to tear this apart.
 

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Sounds like you did everything but check the pump and/or gauge itself. I don't honestly think 170F water is all that hot, but I could be wrong.
 

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" The IR reads 170F on the upper hose. There is probably some variance for testing on the hose. It also reads 150 on the lower hose."

As said, that's not "hot." I would rely on measurements before the OBDII reading. OTOH, that can tell you if the sender is Kevorked.

Before changing anything, I'd check the instrumentation if that were my readings.
 

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I suppose if you can find the resistance values for the sender, you could use a pot and a muktimeter to check the gauge at different "temperatures".
 

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Discussion Starter · #6 ·
Tested block for exhaust gas i.e. carbon monoxide in antifreeze to determine if head gasket is blown. Results: There was no indication of exhaust gases in antifreeze. Checked from cold to hot for 20 plus minutes. Just to check tester I checked for carbon monoxide in exhaust pipe and tester did detect it as expected. Tester is good.

Using computer ECT to check temperature
At 70 degrees F temp gauge reads far left cold.
At 130 degrees F temp gauge reads 1/4 from cold to hot.
At 148 degrees F temp gauge 1/2 or in the middle.
At 167 degrees F temp gauge read on last wide white line before red (hot)
At 181 F (83C) temp gauge is on red line.

Water flowing. Upper and lower hoses are normal hot. Heater working. A/C working. Fan clutch working.

The sending unit read 140 ohms at 160 Degrees F as it should according to manual.

Problem possibility 1 wire sender, so i will change for the third time. Dealer don't stock. Gauge worked fine until three weeks ago. I wiggle wires no change. After i replace sending unit. I will resistance check gauge somehow. Last option is a dedicated temp gauge, but I will do this only reluctantly.
 

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1998IsuzuRodeoS said:
Teflon sealer for temperature gauge sending unit. I read not to use teflon. Please confirm whether to use any sealants on threads.
No, it needs to conduct electricity. However if that were the problem it would read cold, not hot.
 

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Does the gauge stay up with ignition off? If not, does it peg immediately when the ignition is turned on?
 

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Check the electronic components on the back of the cluster/gauge. If you've troubleshot all the way to the sending unit you only have two avenues left really, the wiring to the gauge or the gauge itself.
 

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Discussion Starter · #11 ·
The temperature goes up slowly. It dies not jump to hot immediately.
The temperature gauge stays hot after key is off. I need to check gauge a few hours latter to see reading before and after turning key.

How would gauge be replaced?
 

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Discussion Starter · #13 ·
Checked gauge after off for several hours, and gauge reding cold.
Grounded wire gauge read above hot.
Removed ground gauge went to cold slowly and completely.
Reconnected band turned ignition on 10 minutes and gauge stayed on cold first wide line.
Today I am getting third coolant sender by AC Delco to try. Last two were no name brands.
 

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Discussion Starter · #14 ·
Update
Installed AC Delco coolant temperature sending unit, and temperature appears good. I tested without driving for an hour. Tomorrow I will road test. Below is a lot if data. I conclude that 10 dash line on temperature gauge is normal. The 8 dash line on the temp gauge is exactly in the middle. I also conclude that the no name brand are not good for Isuzu Rodeo. The no name brands have a name but are not major brands like A C delco, Beck Arnley, Gates, Dayco, etc.

Ambient 76 F
ECT 77F
Temp gauge below first wide white line
608 pm
Fan clutch engaged
610 pm
Line one above wide white line
116F
611
Second line
125F
612
Third line
136F
613 closed radiator cap
Fifth line
152F
614
Sixth line
158F
Fan clutch engaged
615
Seventh line
165F
Lower 82
Upper 95
140F outlet
125F inlet
618
Ninth line
178F
Three before last wide white line
Radiator cap warm now
Upper warm
Lower cool
621
13 dash lines
10 line
179F
Clutch engaged
Upper warm hot
Lower warm
148F outlet
120F inlet
625
10 line
179F
627
10 line
179F
Upper hot
Lower warmer
Outlet 167
Inlet 125
631
10 line
179F
632
Radiator cap warmer
Upper hot
Lower warmer
Outlet 146 F
Inlet 130 F
Radiator outlet 155F
Radiator inlet 145
635
10 line
179F
Engine Off key on
636
9 line
179 F
Note Exactly middle is 8 line
638
9 line
181 F
Radiator outlet 160 F
Radiator inlet 135F
Upper 161F
Lower 104F
Outlet 171 F
Inlet 123 F
642
8/9 in between lines
179 F
643
Engine on
644
9 line
181 F
645
Engine off
Clean coolant residue
Engine on
Ambient 74F
648
10 line
179F
650
Clutch on
10 line
179 F
RPM 757
 

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Discussion Starter · #15 ·
Please let me know if these two pictures of the temperature gauge at normal operating temperature are good or normal for a 1998 Isuzu Rodeo S 4X4 3.2L.

I drove vehicle today for an hour. Coolant temperature was 179 degrees F according to live data scanner.

This is my son's vehicle, and I don't know what a normal gauge reading looks like for this vehicle.

I know temperature is good and normal.

Please share a picture of your temperature gauge at normal operating temperature.
 

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The gauge is too far to the right, it should be in the middle more or less.
The fuel gauge is above the full mark, did you overfill the tank?
Your ABS brake system is inoperative.
 

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Discussion Starter · #17 ·
ABS is next project. I read about a known ABS wiring issue near rear of the vehicle, which I will diagnose. I just had computer updated bu Par-Tech for fuel gauge update, and I just filled up the gas tank. Before the update, the fuel gauge was reading near empty after filling up the fuel tank.

The concern is the temperature gauge. Can the temperature gauge be replaced without replacing the entire instrument cluster?
 

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1998IsuzuRodeoS said:
ABS is next project. I read about a known ABS wiring issue near rear of the vehicle, which I will diagnose. I just had computer updated bu Par-Tech for fuel gauge update, and I just filled up the gas tank. Before the update, the fuel gauge was reading near empty after filling up the fuel tank.

The concern is the temperature gauge. Can the temperature gauge be replaced without replacing the entire instrument cluster?
It can, but have you ruled out a short to ground in the sender wire?
 

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1998IsuzuRodeoS said:
ABS is next project. I read about a known ABS wiring issue near rear of the vehicle, which I will diagnose. I just had computer updated bu Par-Tech for fuel gauge update, and I just filled up the gas tank. Before the update, the fuel gauge was reading near empty after filling up the fuel tank.

The concern is the temperature gauge. Can the temperature gauge be replaced without replacing the entire instrument cluster?
What happens with the ignition on, and sensor disconnected?
 
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