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What is normal running temp for 225 slant six?
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Author:  georgesee [ Fri Apr 17, 2026 1:57 pm ]
Post subject:  What is normal running temp for 225 slant six?
I'd be interested in knowing what the normal and stable running temperature is for a slant six. I have a 65 dodge A-100 running at 195 which seems to be on the high side. And that is after some 10 minutes of driving on city streets. Is this considered too high? I'm wondering if my thermostat may be frozen and that is why? What is the best way to check if I have a bad thermostat? I am running an 180 thermostat.
Author:  Dart270 [ Sat Apr 18, 2026 4:29 am ]
Post subject:  Re: What is normal running temp for 225 slant six?
How are you measuring the temp? Do you have an aftermarket temp gauge with numbers on it? The stock gauges can be very inaccurate. 195 is not too high if it does not keep climbing and just stabilizes there.

Lou
Author:  georgesee [ Sat Apr 18, 2026 9:43 am ]
Post subject:  Re: What is normal running temp for 225 slant six?
Yes, I have a bosch temp gauge with numbers and it appears to read between 195-200-205. I am wondering if a high flow water pump would help lower the temperature?
Author:  georgesee [ Sat Apr 18, 2026 9:46 am ]
Post subject:  Re: What is normal running temp for 225 slant six?
I also burped the radiator by parking the truck on a steep incline and removing the radiator cap. I didn't really see any bubbles while I did this but I did notice that the coolant was moving so would this mean that the thermostat is not stuck?
Author:  Dart270 [ Sat Apr 18, 2026 11:29 am ]
Post subject:  Re: What is normal running temp for 225 slant six?
The temp will run a little hotter than the thermostat rating. The main thing is that it does not continue climbing if you are sitting idling or driving on the highway. 200 is a bit hot for that thermostat, so maybe there is some clogging in the radiator or inside the block.

Lou
Author:  SlantSixDan [ Sat Apr 18, 2026 1:49 pm ]
Post subject:  Re: What is normal running temp for 225 slant six?
Quote:
I'd be interested in knowing what the normal and stable running temperature is for a slant six. I have a 65 dodge A-100 running at 195 which seems to be on the high side.
The thermostat sets the engine's minimum operating temperature, not its maximum.

Start reading here and follow the "next chapter" link at the bottom of the first four chapters (there are five).
Author:  Dutch Dart GT 64 [ Fri Aug 28, 2026 6:37 am ]
Post subject:  Re: What is normal running temp for 225 slant six?
Quote:
Quote:
I'd be interested in knowing what the normal and stable running temperature is for a slant six. I have a 65 dodge A-100 running at 195 which seems to be on the high side.
The thermostat sets the engine's minimum operating temperature, not its maximum.

Start reading here and follow the "next chapter" link at the bottom of the first four chapters (there are five).
I've been running my car last night for the first time in about 4 weeks again and noticed the temperature goes way up. I used to have a themostat that got the gauge right in the middle, more towards the cold in the normal operatin grange. The current one was always a bit more to hot, but let's say in the middle of the normal operating range, but lately it is at the high point of the operating range.
The thermostat still works, opens and closes. there is no leakage, I drive fairly slowly but also take it up to 70mph now and then. The car is as stock as can be. should I put in a thermostat with lower temp and if so, what is the correct thermostat for it?

EDIT: and the correct radiator cap? is there a part number? I can only find 'this will fit, and this will fit' but when I ask questions to these aftermarket sellers, what are the specifications, I get no answer, only that it fits...

thanks again,

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Author:  volaredon [ Fri Aug 28, 2026 8:13 am ]
Post subject:  Re: What is normal running temp for 225 slant six?
Time for a good flush. I like putting something called "iron out" in there after flushing it with straight water the best I can, leave it as just water and pour a cup of iron out in there and let it warm up good, maybe take it around the block even and flush again and see what comes out .. I have an 80s truck 3 row radiator soaking in a mix of that stuff laying on ots back on a set of sawhorses right now ... 2nd round, it's been sitting like this 3'-4 days now, I'm gonna flush it again with the garden hose this weekend.... I can tell already by sloshing it around there's a bunch of loosened up crap in there.
Author:  SlantSixDan [ Fri Aug 28, 2026 11:09 am ]
Post subject:  Re: What is normal running temp for 225 slant six?
Quote:
I used to have a themostat that got the gauge right in the middle, more towards the cold in the normal operatin grange. The current one was always a bit more to hot, but let's say in the middle of the normal operating range, but lately it is at the high point of the operating range.
What are the details on the thermostat presently installed in the engine? Brand, temperature rating, where purchased? Without at least that information, we can't know if you have an actual overheating problem, a wrong thermostat, a need for an engine flush, or what else.
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