wilesre

I installed a L31 (out of a late 90's pickup) and I'm having a hard time finding a temp sensor. The head is machined for a 3/8" NPT and the original for my '70 is 1/2" NPT. I tried using one from the donor engine, but the resistance is way different (3600 Ohms vs 650 Ohms at room temp). I tried the companies that sell gauges, like Auto Meter and they can't help. The guy at Autozone was nice and took the time to find a sensor from a mid-70s pickup that had a 3/8' thread, but the resistance was 2200 Ohms. None of the online sources like Jegs or Summit list the resistance.

Any ideas for sourcing this sensor?

Any thoughts on drilling and tapping the head for the larged port? I am confident in my ability to do it. I just don't know if there was a reason that GM used a small port. Maybe something internally in the way on those Vortec heads. I don't want to have to buy a new head.

Thanks

77C34SPD

I turned mine down in my lathe and rethreaded. There is a picture some where in my album

hugie82

I think the block drain plug is 1/2 npt pipe fitting. Your temp may read a little cooler than if it was placed in the head but only a few degrees.

'75

I have the L31 heads on mine and tapped the hole to 1/2npt, problem solved.

wilesre

Sweet. That's the way I've been leaning. Thanks.

wilesre

I thought about that, and I checked your pic. I wouldn't have guessed there is enough material there to do that. Anyway lack of a lathe will likely force me to another solution. Thanks.

wilesre

Only ones I could find were 1/4 npt. Thanks for the advice though.

jim-81

What about a reducing bushing? 1/2 - 3/8

wilesre

If I had a 3/8 sensor going into a 1/2 hole that would work great (and I would have already done it.)

However, I have a 1/2 sensor going into a 3/8 hole. I could use a reducing coupler and a close nipple, but I think it would stick out too far from the head to get a good reading. Might be a temporary "fix".

qwank

I think drilling a tapping is the easiest way out here

hugie82

There is thermostat housings that had fittings in them. It my not look very nice but it's easy and cheap

Camivette

I have mine in the intake. But that's with votec heads and aftermarket intake.

wilesre

I've seen those. Seems like if I have a problem with overheating it would show up in the head before the top of the thermostat housing, especially if the coolant level is low. Might be an option though, even if it's temporary.

CraigH

Willcox now sells factory senders machined down to fit.

wilesre

I've decided temporarily to us pipe fitting adapters and eventually to drill and tap. Reason being that the brake lines are in the way, even with a right angle drill. At some point I'll need to change the brake fluid - I'll remove those brake lines (and proportioning valve) and do the drill and tap job. Thanks for all the suggestions.

wilesre

I got excited about this until I checked the price: $80!!

I don't think there's $60 worth of machining there.

Anyway, thanks for the info, but at that price I'll stick to my plan.

wilesre

I ordered one of these, which should be me farther inside the engine than a close nipple and reducing coupler.