Stock Temp Gauge vs. Replacement Engine... Who will win? (Need an expert! :))

[jocko]

Ugh. Well, as I settle down to the final details of re-doing my interior, I'm starting to learn why the PO did some questionable things...

Here's my problem - PO had a hideous $5 aftermarket temp gauge bolted under the dash. I just assumed that he installed it because the old gauge stopped working. Maybe not the case. When I went to re-install my refurbished dash, I knew I needed to check the wiring and run the temp sender wiring through the normal instrument cluster harness (i.e. cia the circuit board). So, went about finding the discarded (i.e. hidden under the brake booster, out of sight) original temp sender wiring harness. That was good that I found it! Then, planned to swap in an original temp sender since the one in there was probably old, and more importantly, mated/calibrated to the aftermarket gauge. So, after wrestling with the silly spark plug shields so I can get to the sender to remove it, I get it out and find that the hole in the heads is MUCH smaller than the hole required to put the replacement TU5 72 Chev 350/stock heads temp sender in. So, while the anti-freeze is pouring all over the floor, I stuff the aftermarket one back in to stem the tide. Anyhoo...

So here I sit, trying to figure out how to solve this - I can't put a stock temp sensor in the heads of this replacement engine, don't want to try to stick it in the manifold intake manifold somewhere because that's "not quite right" and it will read high compared to in the head, and I want to use the stock gauge and not run an under-dash aftermarket one after all the work of restoring the interior.

Here's the engine data:
Current Engine stamping (actually, it's just a sturdy sticker): V0529P34 (can anyone pls point me to a reference of this engine - specs, etc? It was installed in 97 by PO's local dealer, but who knows what year engine it is or how long it sat on the shelf - it's just a stock replacement truck crate engine, but not a center-bolt valve cover type).
It was replaced in approx Sep 1997.

1st Pic shows the aftermarket sender in the head, 2nd pic shows the removed aftermarket sensor to the right of the correct stock one for a 72. I think. 3rd pic is why I want to do this - the resto'ed gauge cluster... I've heard folks on here state that the Wells TU5 (on the left) is the correct replacement sender for a 72 350 with stock heads, so that's what I got - and it looks like the correct one to me, if memory serves. Anyway. I've read several helpful threads on this (still pouring through this one, it's helpful, but haven't found the solution yet http://67-72chevytrucks.com/vboard/s...d.php?t=581719).

So, HOW do I run a stock in-dash temp gauge in a replacement ~1997 Goodwrench 350 with stock 97-ish heads that have the smaller diameter opening that won't fit the stock 72 sender)? Am pretty sure that the aftermarket sender won't work with the stock gauge because it uses different resistance ranges to drive the temp range on the aftermarket gauge. Appreciate your help.

[FirstOwner69]

Send your sensor to board member brian mac to have it machined down and rethreaded. I think he charged me about $20 a couple years ago. By far the "cleanest" way to do this in my opinion.

Jim

[jocko]

My goodness, that's GENIUS! Thanks Jim, will give him a shout.

[FirstOwner69]

I got the info from this post. http://67-72chevytrucks.com/vboard/s...d.php?t=484537 He's mentioned in post 15. His last visit here was April 15, so it's hard to know when he'll see a PM. I'll see if I have othe contact info, but I doubt it.

Jim

[71K20chevy]

Assuming I read it correctly, looks to me like you've got a couple reducers in you head to allow the existing sending unit to fit. If you take them out, the new one you got SHOULD fit.


Edit: Disregard, took a closer look at the pictures and I realized you're out of luck buddy I suppose you could try running the temp gauge off the old sending unit, but I can't recall the resistance range for the sending unit.

[jocko]

thx andy - yep, the multi-hex stuff is on the sender itself, the hole is the hole, so to speak. Ya got me excited there for a minute, then I saw the edit. thanks though!

[jocko]

So, quick follow-up - when I compare where the threads would engage (even if one on the left is turned down and threaded properly), it would appear that the correct 72 sender on the left would extend significantly further into the head than the aftermarket one. Looks like the aftermarket one on the right doesn't even have a probe that sticks into the water stream, but that may not necessarily be required. I noticed that the brass is all one solid piece (otherwise this probably wouldn't work...) so, once turned down enough to cut new threads, is the remaining probe part that is inserted into the head first turned down further to clear the hole? Is it shortened too so it doesn't stick in too far? Just curious.

[FirstOwner69]

Originally Posted by jocko

So, quick follow-up - when I compare where the threads would engage (even if one on the left is turned down and threaded properly), it would appear that the correct 72 sender on the left would extend significantly further into the head than the aftermarket one. Looks like the aftermarket one on the right doesn't even have a probe that sticks into the water stream, but that may not necessarily be required. I noticed that the brass is all one solid piece (otherwise this probably wouldn't work...) so, once turned down enough to cut new threads, is the remaining probe part that is inserted into the head first turned down further to clear the hole? Is it shortened too so it doesn't stick in too far? Just curious.

When mine was done, the non-threaded probe part was not machined or changed in any way at all. Incidently, the other sensor that was used with the aftermarket gauge will probably not work with a factory gauge. There have been quite a few threads about trying to find sensors for heads with 3/8" NPT threads. Maybe try a search for "Vortec temperature" or some such thing.

[Lattimer]

I gave up on that and just put mine in the manifold, then added a resistor in line with the sensor to make the gauge sit in the middle when the engine is warmed up and the coolant is around 185. Works perfect that way. Not 100% correct, but nether is anything else on my truck.

[jocko]

ha, i'll keep that approach in mind. Why did you decide to give up Lattimer?

[Lattimer]

I read a bunch for threads on getting a sender to fit the smaller hole and work with our gauge when I was swapping in the gauge cluster for the idiot light cluster. Didn't see a lot of success stories. So I decided to just try it in the manifold and see what happened. I still had an aftermarket gauge in the truck at the time also.

The gauge was about 80% of the way to the right all the time, but didn't move much once the truck was warm. That seemed right, since the aftermarket gauge stayed right around 185-190 all the time. So I did some searching on calibrating the gauge and found some good posts with instructions on adding a resistor. Quick trip to Radio Shack and the gauge is dead center at normal operating temp.

Keep in mind---nothing much mechanical on my truck is original, and I didn't want it original. So it didn't matter to me, as long as its functional.

[danheit]

So I'll be curious to see this one as well, as I ran into the same issue. I went as far as contacting GP Sorenson to see if they make a sender, for a different application, that would work.....no dice. Keep us posted on what you do.

[jwatson355]

I have the aftermarket sending unit with the original gauge in my truck. It reads about 70% to the right so it appears to be hot, but running the other gauge for a while seeing that it's running on average 185 degrees, I've learned thats where it reads. I have the original sending unit just waiting for a brain fart so I can use it.

[MARKDTN]

Early heads (before 1975 I think) have a "big" hole. Later heads have a "small" hole. Try a sender for an 1980 Corvette.

[Tx Firefighter]

One of these along with a drill bit and you're ready to put the original sender in. Cast iron drills and taps super easy. You've already got a pilot hole there so there's not much material to remove.

[jocko]

Originally Posted by MARKDTN

Early heads (before 1975 I think) have a "big" hole. Later heads have a "small" hole. Try a sender for an 1980 Corvette.

Thanks Mark - yes, that is the problem, however just using the later sender won't give correct readings on the 72 gauge - different resistance ranges in the sender. I could give this a shot as a last resort and try to fix the readings with resistors as mentioned above, but I'd prefer to make the correct sender work with the factory gauge. I may need to go this way eventually.

Originally Posted by Tx Firefighter

One of these along with a drill bit and you're ready to put the original sender in. Cast iron drills and taps super easy. You've already got a pilot hole there so there's not much material to remove.

Thx Kevin - I think I'd choose this route if I had the heads off. I have heard folks doing this and maintaining the chips on the tap with grease, etc, but have to admit I think I'd only be comfortable doing this if I had the heads off and I could confirm I got all the chips out - otherwise run the risk of fouling the water pump or clogging a passage. But, agree this is the BEST approach.

I think I will try the turning down of the TU5 first, if it seals and works, yay, if not, I'm only out a few bucks for another sender and then I'll yank the head.

Thanks gents. If I don't hear from Brian Mac, I may ping my local machine shop, have a decent one here.

[Tx Firefighter]

Bah, no reason to get excited about the shavings. I can offer you a suggestion on that.

Take your thermostat out and bolt the water neck back down. Now, put a garden hose down the water neck and shove a rag tightly around it to make a sort of seal. Now, with the garden hose flowing at a slow trickle, do your drilling and tapping. The outflow of water through the sending unit hole in the head will flush out any drilling and tapping shavings as they occur.

A little messy, drilling and tapping a hole with water coming out of it, but it damn sure beats pulling the head. You should be able to adjust the flow slow enough to not be overwhelming, yet still steady enough to flush your shavings.

[jocko]

Thx Kevin!

[Fitz]

Originally Posted by Tx Firefighter

Bah, no reason to get excited about the shavings. I can offer you a suggestion on that.

Take your thermostat out and bolt the water neck back down. Now, put a garden hose down the water neck and shove a rag tightly around it to make a sort of seal. Now, with the garden hose flowing at a slow trickle, do your drilling and tapping. The outflow of water through the sending unit hole in the head will flush out any drilling and tapping shavings as they occur.

A little messy, drilling and tapping a hole with water coming out of it, but it damn sure beats pulling the head. You should be able to adjust the flow slow enough to not be overwhelming, yet still steady enough to flush your shavings.

As always, Kevin you are a lone voice of reason in a BS storm!

[jocko]

huh?

[Tx Firefighter]

I don't think he was referring to this thread specifically. In general, I try to offer simple and easy solutions in various threads. I'm just lazy really. There is no more romance to me about pulling cylinder heads. Anything to avoid it if possible.

[Fitz]

Originally Posted by jocko

huh?

The simplest solution is always the best solution. The correct size drill and a tap to match the sender threads will work, it can be done in less time than looking up the phone number for someone to machine the replacement sender and re-thread it. Far better than sending it off, waiting for the guy to get around to machining it, and send it back. Flowing water through the jacket while you drill and tap keeps chips out so they won't plug the tubes in your rad and you don't need to pull the head to get the job done.

My grandfather told me when hiring a man to do a job, look for a lazy man. He will know or find the fastest , cheapest way do get something done without making a mess you will make him clean up thus saving himself time and you aggravation.

So, when you say ,"HUH" what you are really saying is "DUH"!

[brian mac]

Op pmed me to see this thread . There are many ways to skin a cat. Here is another suggestion. Drill with proper tap drill for 1/2 inch pipe. Vacuum shavings from hole with shop vac and tube small enough to reach in hole. Pack flutes of tap with wheel bearing grease to contain the swarf created from tapping the new threads. Or send a new sending unit and 20 bucks to
Brian McCullough
113 red oak lane
Eufaula,al. 36027 and I will re-thread it to 3/8 pipe. If you purchase tap drill and tap it will be more than 20 bucks.

[FirstOwner69]

I wasn't going to say any more on this subject, but after reading all the responses and looking at the options, I thought I should state why I decided to have my sensor re-threaded.

I figured this was the lowest risk option. Risk $20 and a sensor to have it re-threaded or risk screwing up the head on my new engine. Sure, I probably would have been successful on modifying the head, but I'd want to practice on a junk head first. Both will work. Both at least appear original. AND, it was less work for me. I'm lazy too!

[jocko]

That is exactly why I'm going to do this - lowest risk first, and the cost is still very low also - I suspected the tap was more than Brian's fee.

Brian Mac - been a way from my comp for a few days - expect this in the mail soon!
Thanks,
Jocko