Coolant temp issue
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4th Gear
Joined: Feb 2025
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Coolant temp issue
Ive been having overheating symptoms in my 97 250hd with the 5.8. The factory dash gauge is pinned on H. I know these are dummy gauges so I plugged an aftermarket gauge into the OEM port in the intake manifold. This gauge reads about 260. Here's the kicker, when I temp gun my thermostat housing and upper rad hose it reads about 200. What would cause much higher temps in the intake manifold? I've been ignoring the gauge since my tstat housing seems to be about the right temp. Am I a fool for this? The only thing I can think of that would cause this issue is maybe a blocked coolant passage? Anyone had this issue before? New water pump, radiator, and hoses, all flushed bled and pressure tested.
Hotshot
Joined: Jun 2015
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Is it actually overheating or not? What happens to the gauge when you unplug the wire from the sending unit? Your assumption is wrong about it not being a real gauge. So you have the factory gauge and an aftermarket gauge both telling you it is too hot and you’re ok with that result? New thermostat?
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4th Gear
Joined: Feb 2025
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Is it actually overheating or not? What happens to the gauge when you unplug the wire from the sending unit? Your assumption is wrong about it not being a real gauge. So you have the factory gauge and an aftermarket gauge both telling you it is too hot and you’re ok with that result? New thermostat?
It seems like I'm overheating in the manifold, but not elsewhere. I'm not boiling off my coolant as far as I can tell. The overflow reservoir isn't filling.
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4th Gear
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Radiator is full and the overflow is full to the cold line. I would expect if I was running at 260 coolant temp as the gauge suggests the overflow would be full when the engine is hot.
I don't think I'm having "real" overheating issues based on what my temp gun readings are. 190 at tstat housing and about 210 head temp.
I'm wondering if anyone has insight on why the factory sender location seems to read higher than what the temp gun would suggest. Ive validated the factory gauge reading with two separate aftermarket gauges in the same sending location.
Lead Driver
Joined: Jun 2021
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Yeah the needle starts at cold and goes to H as the truck warms up then stays pinned. The tstat is opening my upper rad hose is reading at about 160 with a temp gun once the housing passes 190 and t stat opens.
Radiator is full and the overflow is full to the cold line. I would expect if I was running at 260 coolant temp as the gauge suggests the overflow would be full when the engine is hot.
I don't think I'm having "real" overheating issues based on what my temp gun readings are. 190 at tstat housing and about 210 head temp.
I'm wondering if anyone has insight on why the factory sender location seems to read higher than what the temp gun would suggest. Ive validated the factory gauge reading with two separate aftermarket gauges in the same sending location.
Radiator is full and the overflow is full to the cold line. I would expect if I was running at 260 coolant temp as the gauge suggests the overflow would be full when the engine is hot.
I don't think I'm having "real" overheating issues based on what my temp gun readings are. 190 at tstat housing and about 210 head temp.
I'm wondering if anyone has insight on why the factory sender location seems to read higher than what the temp gun would suggest. Ive validated the factory gauge reading with two separate aftermarket gauges in the same sending location.
Do you know where the gauge sender is? Whats the wire look like?
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4th Gear
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Both mechanical gauges read about 260 when plugged into this sending location. My first thought was it was an issue with the cluster, so I verified that the gauge.
Again I'm wondering if anybody can think of a reason coolant would be hotter at the sending location on the intake manifold than at the tstat housing.
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Lead Driver
Joined: Jun 2021
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The sender is in the intake manifold near the distributor. It's one wire to the dash. Ive verified the reading with two aftermarket gauges (including aftermarket senders) plugged into the same port.
Both mechanical gauges read about 260 when plugged into this sending location. My first thought was it was an issue with the cluster, so I verified that the gauge.
Again I'm wondering if anybody can think of a reason coolant would be hotter at the sending location on the intake manifold than at the tstat housing.
Both mechanical gauges read about 260 when plugged into this sending location. My first thought was it was an issue with the cluster, so I verified that the gauge.
Again I'm wondering if anybody can think of a reason coolant would be hotter at the sending location on the intake manifold than at the tstat housing.
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Hotshot
Joined: Jul 2020
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From: Near Salt Lake City
The sender is in the intake manifold near the distributor. It's one wire to the dash. Ive verified the reading with two aftermarket gauges (including aftermarket senders) plugged into the same port.
Both mechanical gauges read about 260 when plugged into this sending location. My first thought was it was an issue with the cluster, so I verified that the gauge.
Again I'm wondering if anybody can think of a reason coolant would be hotter at the sending location on the intake manifold than at the tstat housing.
Both mechanical gauges read about 260 when plugged into this sending location. My first thought was it was an issue with the cluster, so I verified that the gauge.
Again I'm wondering if anybody can think of a reason coolant would be hotter at the sending location on the intake manifold than at the tstat housing.
The rest of the time the housing will be cooler than the intake or the heads
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