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Old 07-10-2018, 02:59 PM
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Default What coolant temperature sender?

Working on K5 1970 Blazer. Has a gauge not a light to monitor engine temp. Put in a later 383 engine and the hole for the sender is 3/8" npt not 1'2"npt which is what the old one is. The original sender is 70-88 ohms at 220'. Anyone know what sender will work with the gauge that has 3/8"npt thread?
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Old 07-11-2018, 08:41 AM
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I'm sure someone has been here before swapping in a later engine! So can anyone tell me what the ohm temp readings should be for 100' and 220'?
I contacted VDO and with the temp/ohms they can find the correct sender.
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Old 07-11-2018, 11:40 AM
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I would get a 3/8 male npt to 1/2 female npt adapter (like
THIS ONE THIS ONE
) and use the original sender. If height becomes an issue, get a 90 degree fitting with 3/8 male npt and 1/2 female npt.
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Old 07-11-2018, 11:54 AM
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Thanks for the suggestion. I thought about this type of adapter but saw this as a less than perfect solution. I'm thinking that the probe end of the sender will be hidden from the coolant and would not give as accurate a reading. I should order a fitting like that but my other concern is the probe end will bottom out before the threads engage.
I do appreciate your input!
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Old 07-11-2018, 12:07 PM
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If you had clearance to drill and tap the 3/8 hole to 1/2 on the intake the aluminum is easy digging.
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Old 07-11-2018, 12:44 PM
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I thought about enlarging the hole in the head to 1/2npt but discounted due to clearance issues. The intake manifold on this crate motor looks like GM is out to save Aluminum, not enough meat . Doesn't look like enough depth either to run a tap in far enough to cut full threads.
I ordered a fitting as suggested by Swartikk (?) and if that doesn't pan out I guess accessory gauges are in order.
Again, thanks for the suggestions.
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Old 07-11-2018, 06:08 PM
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I have to apologize. I read this thread quickly on my phone while I took a break this morning and swore I saw oil pressure sending unit. You are correct in that the adapter I recommended would not allow for the tip of the sending unit if your sender is like what's on my '70 Chevelle & '74 Blazer.

Are you sure of your resistance values? Most GM temperature sending units would be somewhere around 145 ohms at 220F. What is it at room temp (~70F)?

In a bit of web searching, I saw that there were some recommendations to using the Standard Motor Products TS76 sending unit, but I could not find the resistance chart for that sensor. It may also have a different connector than your stock sensor. You could test the TS76 against your stock sender to determine if the resistance values are consistent prior to installation so that you could return it if necessary.

And THIS POST on CorvetteForum.com shows some resistance values for the Duralast TU66 sensor and is stated to work in the newer heads. It also suggests using on of the ports on the front cross-over in the intake manifold which I'm not sure if you've looked into or not.
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