Won't warm up even in 100* weather - Dodge Cummins Diesel Forum
94-98 Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission Ect...NO ADVERTISING

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post #1 of 22 (permalink) Old 09-13-2019, 01:44 PM Thread Starter
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Won't warm up even in 100* weather

I have SEARCHED. I have advanced searched. I read and read. I replaced the thermostat with a genuine cummins stat. I pulled that new stat back out and tested it in boiling water. It moved at ~185*. I am STUMPED... Here is the whole story...

Had the head replaced (I cracked it) by Power Driven Diesel. Ran fine for 200-300 miles then the temp gauge just dropped to about 150*. Within another 100 miles it suddenly dropped to 140 (I watched it plummet) and stayed there. This is dead of summer - 115* in the southern Nevada heat. Called PDD and they said probably a bad Tstat. So I went to cummins and got a new one based on my vin (can't get more specific than that). Replaced it and fired it up for a test drive. NOPE... no movement, so I plugged in the block heater, let it work over night and THEN drove it - gauge read ~150*.

Pulled the new tstat and tested it as recommended repeatedly here on CF. Worked fine if the internal piece sliding along is all that is supposed to happen. I have never seen a Tstat function, but it did it repeatedly and consistently.

Got to thinking maybe a bad gauge or sensor. Got an inferred heat thermometer. Temp at the thermostat after a drive is 180. That is good. Gauge in the cab still reads 140. NO HEAT in the cab... OK it is very luke warm.

SO NOW WHAT? If the stat is working WHY OH WHY is the engine not warming? Any and all ideas are welcome.

I have winter coming and do not want to be running this thing cold. I know some do, but everything I read and even PDD said cold is VERY BAD. I don't care if the gauge doesn't work, but I want to know the engine is warm. I have the downloaded shop manual and it says the sensor is at the top of the block, drivers side, way back behind the fuel filter... all I found there is a plug. Am I mistaken where the sensor is? I would buy a ISSPRO gauge if someone will tell me where to put the sensor in the engine.

Thanks for the help everyone. Love this forum and all the gurus here.


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post #2 of 22 (permalink) Old 09-13-2019, 06:06 PM
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The temp sensor is behind the p-pump and under the intake shelf. It is very difficult to get to and very difficult to see. I believe the '98 has two wires to it. They seldom fail. If you are reading 180 at the t-stat your system is operating normally. The gauge isn't an accurate measure so I suspect if you went through the trouble of changing sensors the gauge would still read low. The heater not working is a separate matter. There is a ton of info, mostly posted in the winter, and it always amounts to the same answers. T-stat (yours is working) and heater core. The cores sometimes can be back flushed. They can be packed with dirt and dog hair or they might be plugged, in which case you need to drop the dash to get to the plenum.
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post #3 of 22 (permalink) Old 09-15-2019, 10:45 AM
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Not to mention blend doors.

R12 in the summer, Webasto in the winter, and cassette tapes all year.
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post #4 of 22 (permalink) Old 09-15-2019, 02:27 PM
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Not to mention blend doors.
Yup, forgot that one.

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post #5 of 22 (permalink) Old 09-15-2019, 03:59 PM
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Sounds like a bad temp gauge...get a real gauge, and check your blend doors for proper function. I had a very similar thing happen to me this summer, driving along in 110 deg heat and looked down to see 140 deg on the temp gauge! It was a brand new Mishimoto thermostat, and it must have stuck open. I went back to a OEM stat, and all is good.

Now I don't use a block stat any longer, but a digital temptroller. It holds the temp I tell it to regardless.
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post #6 of 22 (permalink) Old 09-16-2019, 01:17 AM
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Quote:
Originally Posted by Gator1 View Post
Sounds like a bad temp gauge...get a real gauge, and check your blend doors for proper function. I had a very similar thing happen to me this summer, driving along in 110 deg heat and looked down to see 140 deg on the temp gauge! It was a brand new Mishimoto thermostat, and it must have stuck open. I went back to a OEM stat, and all is good.

Now I don't use a block stat any longer, but a digital temptroller. It holds the temp I tell it to regardless.
Please tell me about this "digital temptroller".
Thanks,
David

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post #7 of 22 (permalink) Old 09-16-2019, 10:56 AM Thread Starter
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[/QUOTE]
Now I don't use a block stat any longer, but a digital temptroller. It holds the temp I tell it to regardless.[/QUOTE]

I'm interested too.

I would LOVE to add an aftermarket gauge, but WHERE and how? I know that the ISSPRO (my prefered gauge) sells one and if I recall correctly it comes with a 1/4" sensor. So can I drill and tap? My main question remains... WHERE?

I will look into and read up on the heater core. I am relieved that it is not a cold engine issue. Also I found the sensor in the location mentioned here, but it wasn't where I thought it "should" be.

I guess I will tackle one issue at a time. First is the heater core, unless someone thinks there is a better order. The blend door sounds like a terrible job.

Thanks everyone.

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post #8 of 22 (permalink) Old 09-16-2019, 10:59 AM
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Check out the "going electric" thread.

03 Dodge SHO QCLB Dually w/Custom side exit exhaust-Banks intercooler-4" side draft intake-Thuren 3.0 Argon filled Shocks-radius arms-SRW 4 link Conversion-17"methods-42" Squishy's- 4.56's-Griffin Radiator-elec fans & water pump=25.263 mpg legit.
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post #9 of 22 (permalink) Old 09-16-2019, 11:06 AM
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Now I don't use a block stat any longer, but a digital temptroller. It holds the temp I tell it to regardless.[/QUOTE]

I'm interested too.

I would LOVE to add an aftermarket gauge, but WHERE and how? I know that the ISSPRO (my prefered gauge) sells one and if I recall correctly it comes with a 1/4" sensor. So can I drill and tap? My main question remains... WHERE?

I will look into and read up on the heater core. I am relieved that it is not a cold engine issue. Also I found the sensor in the location mentioned here, but it wasn't where I thought it "should" be.

I guess I will tackle one issue at a time. First is the heater core, unless someone thinks there is a better order. The blend door sounds like a terrible job.

Thanks everyone.[/QUOTE]

The sensor should go right where the OEM one is on the head. It should be plug and play after you decide where to put the gauge. In a pod on steering wheel, or A-pillar are most common places.

Edit: if I remember right the OEM sensor is not a NPT but a crush washer seal, so remove one of the plugs in the head along the passenger side and replace with an adapter for a 1/4" npt. or drill and tap the Stat housing etc.

03 Dodge SHO QCLB Dually w/Custom side exit exhaust-Banks intercooler-4" side draft intake-Thuren 3.0 Argon filled Shocks-radius arms-SRW 4 link Conversion-17"methods-42" Squishy's- 4.56's-Griffin Radiator-elec fans & water pump=25.263 mpg legit.
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post #10 of 22 (permalink) Old 09-16-2019, 11:53 AM
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Quote:
Originally Posted by Big Red Mega View Post

I guess I will tackle one issue at a time. First is the heater core, unless someone thinks there is a better order. The blend door sounds like a terrible job.
The blend door on '97s and earlier is controlled by a cable. I suspect yours is also, but it might be an electric motor. If it is a cable, accessing it is as much work as replacing the heater core.
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post #11 of 22 (permalink) Old 09-16-2019, 11:58 AM
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Quote:
Originally Posted by Gator1 View Post

The sensor should go right where the OEM one is on the head. It should be plug and play after you decide where to put the gauge. In a pod on steering wheel, or A-pillar are most common places.

Edit: if I remember right the OEM sensor is not a NPT but a crush washer seal, so remove one of the plugs in the head along the passenger side and replace with an adapter for a 1/4" npt. or drill and tap the Stat housing etc.
The only way I would put the sensor where the OEM one is located would be if the engine was removed from the truck. It is NPT.

https://www.genosgarage.com/product/...gine-sensors-2

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post #12 of 22 (permalink) Old 09-16-2019, 12:28 PM
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Quote:
Originally Posted by GAmes View Post
The only way I would put the sensor where the OEM one is located would be if the engine was removed from the truck. It is NPT.

https://www.genosgarage.com/product/...gine-sensors-2
Mine is in a much easier to reach spot, and different year might be npt, but even the one in that pic from Geno's looks to be an o-ring washer, or aluminum crush washer type.

03 Dodge SHO QCLB Dually w/Custom side exit exhaust-Banks intercooler-4" side draft intake-Thuren 3.0 Argon filled Shocks-radius arms-SRW 4 link Conversion-17"methods-42" Squishy's- 4.56's-Griffin Radiator-elec fans & water pump=25.263 mpg legit.
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