Stock temp. sending unit in a Vortec engine - The 1947 - Present Chevrolet & GMC Truck Message Board Network

poff · 09-16-2004, 02:03 AM

As many know the new Vortec heads have a 3/8" NPT hole for the temp. sending unit, stock for my '70 at least is 1/2" NPT. Well for lack of a better solution, I ended up putting my temp. sending unit in the intake. This interfered with my thermostat housing. I found a solution if anyone has the same problem. A company called PRC or Performance Rod and Custom makes a 1" thermostat housing spacer. I think the real purpose is a bypass for aluminum heads or something. It has two 3/8" NPT holes in it, I just pluged them and put them faceing back. Their # is 812-997-5905.

68C15 · 09-16-2004, 07:33 AM

or you could have tapped the head for 1/2 NPT & kept the sender where it is more accurate. on the norm there is about 10* diff. between the head & intake. I recommend using your new spacer to plumb some lines from back of intake to bottom of therm.

poff · 09-16-2004, 10:18 AM

I talked to several different people about it and came to the same conclusion about accuracy. I considered drilling out the head but I did not want mess with my brand spankin' new engine. Especially didn't want to chance voiding the warranty. Never really had cooling problems before, plus the radiator is huge. I do not recall seeing any provisions for coolant hoses on the rear of the intake.

Woody · 09-16-2004, 11:01 AM

There was a post about this before. What you need is a temp sender for a early 70's volvo. It is the right size and calibrated for the stock guage. Sorry I don't have a p/n.

**MikeB** · 09-16-2004, 12:21 PM

I had the same problem on my 350, but lucked out and found an OEM t-stat housing (from an 80s or 90s engine, I think). The hose neck on the OEM housing sits higher and angles upward more than on aftermarket chrome housings. The Performer EPS manifold t-stat mounting pad is also higher relative to the 1/2" pipe port, compared to something like a regular Performer manifold.

I also have a mechanical gauge connected to the cylinder head just to test and calibrate my OEM gauge (no numbers). So even if the head temp is 10 degrees higher, it doesn't matter with an OEM gauge.

In fact, my 55 Chevy has gauges in both the head and manifold ports, and there is a little difference at idle, but virtually none at highway speeds. Heat rises, does it not?

poff · 09-16-2004, 01:52 PM

Certainly worth investigation. Thanks.

Woody · 09-16-2004, 02:29 PM

Poff,

Someone posted a brand & p/n of a sending unit that worked. I know I printed it off & put it in my file of 67-72 truck tips. Yuo might try a search or wait a little longer and see if someone else posts what you need. Sorry I don't have the info at work here or I would post it.

nturner · 09-16-2004, 03:38 PM

Woody --- If you could find the brand/PN somewhere Me and lots of others would be very greatful. Have a new crate motor with vortec heads and have a patch job now --- a sender that fits the 5/8ths threads would be fantastic. Thanks, Noel

72k5 · 09-16-2004, 06:30 PM

FWIW,
I tried the Volvo sender and it didn't work for me. The Volvo sender has straight threads and a gasket - like a spark plug. The head is a tapered pipe thread. I had visions of stripped aluminum threads and leaking coolant.

I like the photo of the stock sender in the intake. It would never work with my stock outlet, but you give me hope that I might find an outlet that would.

Mike

jimfulco · 09-17-2004, 02:40 AM

Will a 1/2" x 3/8" reducer bushing work?

poff · 09-17-2004, 09:19 AM

I looked at them, they stuck out too far and did not have enough clearance for coolant flow. I was afraid I would get more exhaust heat than coolant temp.

Woody · 09-17-2004, 11:45 AM

Ok Guys, I'll try to look it up this evening after I get home.

PMS · 09-17-2004, 05:46 PM

I ran into the same problem. I just used a thermostat housing from a 67 V8 and upper radiator hose and mounted the original sender in the intake.

09-16-2004, 02:03 AM	#1
poff Registered User Join Date: Dec 1999 Location: san diego, ca Posts: 546	Stock temp. sending unit in a Vortec engine As many know the new Vortec heads have a 3/8" NPT hole for the temp. sending unit, stock for my '70 at least is 1/2" NPT. Well for lack of a better solution, I ended up putting my temp. sending unit in the intake. This interfered with my thermostat housing. I found a solution if anyone has the same problem. A company called PRC or Performance Rod and Custom makes a 1" thermostat housing spacer. I think the real purpose is a bypass for aluminum heads or something. It has two 3/8" NPT holes in it, I just pluged them and put them faceing back. Their # is 812-997-5905. __________________ '70 K-20 San Diego, CA Last edited by poff; 09-16-2004 at 07:03 PM.

09-16-2004, 07:33 AM	#2
68C15 blood type; Retumbo Join Date: Jan 2004 Location: next to my reloading bench Posts: 10,269	or you could have tapped the head for 1/2 NPT & kept the sender where it is more accurate. on the norm there is about 10* diff. between the head & intake. I recommend using your new spacer to plumb some lines from back of intake to bottom of therm. __________________ Man rule #77...if you own a 67 stepside with a caddy 472 you will never be in danger of loosing you man card

09-16-2004, 10:18 AM	#3
poff Registered User Join Date: Dec 1999 Location: san diego, ca Posts: 546	I talked to several different people about it and came to the same conclusion about accuracy. I considered drilling out the head but I did not want mess with my brand spankin' new engine. Especially didn't want to chance voiding the warranty. Never really had cooling problems before, plus the radiator is huge. I do not recall seeing any provisions for coolant hoses on the rear of the intake. __________________ '70 K-20 San Diego, CA

09-16-2004, 12:21 PM	#5
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,464	I had the same problem on my 350, but lucked out and found an OEM t-stat housing (from an 80s or 90s engine, I think). The hose neck on the OEM housing sits higher and angles upward more than on aftermarket chrome housings. The Performer EPS manifold t-stat mounting pad is also higher relative to the 1/2" pipe port, compared to something like a regular Performer manifold. I also have a mechanical gauge connected to the cylinder head just to test and calibrate my OEM gauge (no numbers). So even if the head temp is 10 degrees higher, it doesn't matter with an OEM gauge. In fact, my 55 Chevy has gauges in both the head and manifold ports, and there is a little difference at idle, but virtually none at highway speeds. Heat rises, does it not? Attached Images __________________ Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!

09-16-2004, 01:52 PM	#6
poff Registered User Join Date: Dec 1999 Location: san diego, ca Posts: 546	Certainly worth investigation. Thanks. __________________ '70 K-20 San Diego, CA

09-16-2004, 11:01 AM	#4
Woody Registered User Join Date: Feb 2000 Location: Georgetown, KY, USA Posts: 631	There was a post about this before. What you need is a temp sender for a early 70's volvo. It is the right size and calibrated for the stock guage. Sorry I don't have a p/n.

09-16-2004, 02:29 PM	#7
Woody Registered User Join Date: Feb 2000 Location: Georgetown, KY, USA Posts: 631	Poff, Someone posted a brand & p/n of a sending unit that worked. I know I printed it off & put it in my file of 67-72 truck tips. Yuo might try a search or wait a little longer and see if someone else posts what you need. Sorry I don't have the info at work here or I would post it.

09-16-2004, 03:38 PM	#8
nturner Registered User Join Date: Nov 2003 Location: Stockton, CA Posts: 31	Woody --- If you could find the brand/PN somewhere Me and lots of others would be very greatful. Have a new crate motor with vortec heads and have a patch job now --- a sender that fits the 5/8ths threads would be fantastic. Thanks, Noel __________________ Vagabond '55

09-16-2004, 06:30 PM	#9
72k5 Registered User Join Date: Oct 2002 Location: Livermore, CA Posts: 566	FWIW, I tried the Volvo sender and it didn't work for me. The Volvo sender has straight threads and a gasket - like a spark plug. The head is a tapered pipe thread. I had visions of stripped aluminum threads and leaking coolant. I like the photo of the stock sender in the intake. It would never work with my stock outlet, but you give me hope that I might find an outlet that would. Mike __________________ 350 ETec 170 heads, Performer, HEI, Holly TBI, 700r4, 14 bolt rear, F&R lockers, lots of off road improvements.

09-17-2004, 02:40 AM	#10
jimfulco Registered User Join Date: May 2003 Location: Shreveport LA Posts: 3,170	Will a 1/2" x 3/8" reducer bushing work?

09-17-2004, 09:19 AM	#11
poff Registered User Join Date: Dec 1999 Location: san diego, ca Posts: 546	I looked at them, they stuck out too far and did not have enough clearance for coolant flow. I was afraid I would get more exhaust heat than coolant temp. __________________ '70 K-20 San Diego, CA

09-17-2004, 11:45 AM	#12
Woody Registered User Join Date: Feb 2000 Location: Georgetown, KY, USA Posts: 631	Ok Guys, I'll try to look it up this evening after I get home.

09-17-2004, 05:46 PM	#13
PMS Registered User Join Date: Aug 2004 Location: Overland Park, KS Posts: 79	I ran into the same problem. I just used a thermostat housing from a 67 V8 and upper radiator hose and mounted the original sender in the intake.



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