'65 rally cluster temperature gauge pegged.

[Lfowler]

Hi Group. I'm stuck with a temperature gauge problem on a '65 rally gauge car. It reads full (pegged) all the time the ignition is on. This developed over a few weeks time about 15 years ago. The car has been mostly stored since. I tried to fix it a couple of times over the years without making much progress (gauge wise) by installing the HD radiator option, correct fan shroud, new sender, and basic quick wiring checks. It didn't heal up on it own either so I started troubleshooting yesterday. I suspect the "new" sender is not of the correct resistance value as the old one. I suspect the car may have had an over heat problem that the radiator corrected but by then the "old" good sender had been replaced and created a new problem that looked like the origional failure.

I've had that come up on several mid '60 corvettes and eventually found NOS senders.

Is anyone up to date on sender resistance values for that application? Thanks.

[Brandon]

I just checked the stock sending unit on my '66. At 70° it is 740 Ohms. What is yours measuring at room temperature?

[Lfowler]

The sender in my car is showing 670 @ 65 degrees. Unknown brand.
A new Standard sender #TS-6 is 607 @ 65 degrees.

I'll get a few resistors and see if I can "tune" the circut in my car baised off 740 ohms and post the results. Thanks very much. This has bugged me for a very long time.

[Brandon]

I just tried a couple things on my '66. First I disconnected the sending unit, to simulate an open (broken wire) - the temp gauge read min temp. Then I shorted the sending wire to ground, and the temp gauge read max temp. If your temp gauge is pegged to max as soon as you turn on your ignition, then I suspect that the sending wire is shorted to ground. Try this:
1. Turn off your ignition.
2. Disconnect your temp sending unit.
3. Meas resistance from ground to the sending unit - you should see about 600-700 Ohms.
4. Meas resistance between ground and the wire going to the temp gauge. If I'm right, you will see less than a couple Ohms. If so, then the short is either in the wiring or in the temp gauge itself.

[Lfowler]

Hi Brandon, I suspect my sender wire is shorted also. The problem is where.

Regarding your number 3: I get anywhere from 500 to 1000 ohms through the disconnected sender to ground depending on what mfg's sender I have in the circut. Sender to ground resistance doesn't change between the manifold, alternator case, or the battery itself. I'm OK with that part of the circut.

Regarding your number 4: I pulled the dash and got to the gauge connector for a good look. The vehicle wiring is in great shape. Nothing hacked or changed from OEM except two added gauges (S/W on a completely seperate circut). The rally gauge loom seems to be an added on deal seperate from the main harness. Pink wire picks up power at the ignition key and feeds both water temp and oil pressure gauges as per schematic. Battery voltage available when key on and not when key off. Oil presssure gauge reads correctly and functions correctly on blue coded wire. Green coded wire is isolated from both pink and blue wires and seems to be isolated from ground. Green wire phyically goes from gauge to temp sender in one run. Continunity of green wire is good. There is a brown wire in the loom I haven't figured out yet.

When I substute a NOS temp gauge in the circut it behaves the same as my origional gauge and if I reverse polarity of the gauges they peg down scale in a similar failure mode. If I swap the oil pressure gauge for the temp gauge it reads,"fails", the same way. So I conclude I have good gauges capable of functioning correctly if the wiring was right. So I put all that back together and went back to the wiring.

I disconnected the green wire at the sender and gauge and ran a sepertate wire over the windshield to take it's place. The gauge still pegged when the key was turned on. I sustuted the NOS gauge hanging in air into the circut and had a similar failure mode. Grounding the gauge cases made no difference nor did removing the oil presssure gauge from the circut.

So I feel I'm missing something basic about the green wire(s). I think the next step is to pull the loom out and inspect it for a hidden chaffed spot and redo my seperate wire test to be sure I was really isolated.

Thanks for your advise. I appreciate the reality check.

On slightly different subjects: My gauge cluster is equipped with a lens for a parking brake indicator light but nothing is filling the backside hole, nor is there a switch on the foot pedel. Was that an add on option? A similar situation exists for the glove box light. There are provisions for the phyical components but nothing is installed. Does anyone have those add on looms and parts available? I'd like to add them to my car.

I noticed you have a '66. Do you want an origional used back seat cover? I threw my '65 rear seat away a long time ago when I installed a roll bar and then purchased a replacement a few years ago from a '66 that has the incorrect (for my car) upholistry pattern. It is in good shape in the embossed areas but the attaching fabric would need replacement. I'm making a custom rear seat to accomidate my roll bar and will put correct pattern material back so this '66 cover became surplus yesterday. It's Free if you want to pay the UPS shipping. Let me know within a few days.

[Brandon]

Green coded wire is isolated from both pink and blue wires and seems to be isolated from ground.
To verify that it is isolated from ground, just meas the resistance between it and ground. It doesn't sound like your green wire is shorting to ground, because when you completly bypassed it the problem remained.

Some thermistors go up in resistance as temp increases, some go down. I doubt that it changed between '65 and '66, but it's a possibility. What does your temp gauge read when the wire to the sender is disconnected at the sender? What if you then connect that wire to ground (or equivlently, short out the temp sender)?

So you've replaced the sender, the wire to the gauge, and the gauge itself, and the problem persists? I'm stumped. :?

On slightly different subjects: My gauge cluster is equipped with a lens for a parking brake indicator light but nothing is filling the backside hole, nor is there a switch on the foot pedel. Was that an add on option? A similar situation exists for the glove box light. There are provisions for the phyical components but nothing is installed. Does anyone have those add on looms and parts available? I'd like to add them to my car.
Can't help you there. Does anyone else know?

Thanks for the seat cover offer, but my back seat is in nice shape.

Good luck, let us know what you find. :)

[Lfowler]

Good Morning Brandon, the sender wire makes no difference in the function of the gauge, connected or not. Calibration of the sender aside, that leads me to believe the problem is "upstream" of the green wire connector at the sender. Or at least upstream as far as the green wire's entry into the remainder of the under hood loom.

I don't think Pontiac changed the thermistor type between '65 and '66 because current aftermarket sender application listings show from early 60's into the '70's using the same part.

I'll be back on this problem tomorrow. The last couple of days has been spent fixing seat frame springs and fabricating a custom seatback for the rear and pulling the heater case / radio out so that stuff can be blasted/painted/rebuilt. My sound deadening insulation has been falling out in lumps so I pulled most of the remainder out yesterday. When I replace it I'll get a good look at the wire looms and retest the green wire. I think I just missed something really basic about it's condition, perhaps hidden in the wads of junk insulation balled up behind the cluster.

Although I've been doing this professionally for more than thirty years now and then something basic can still create a mystery until I back up and think a bit. Thanks for making a quick decision about the seat covers. I've been on a "clean out the shop" program for the last few months and should not get faint hearted about letting them go one way or another. It feels too good to be emptying the storage shelves to stop now.

Best Regard to all.

[Lfowler]

I located an open ground at the gauge case when mounted in the cluster today. I've spent the last two weeks reconditioning the interior and repainting the dashboard itself and every sort of odd maintance thing I haven't done in fifteen years while thinking about this issue. Procrationation all the way.

Today I either had to fix it or put the car back together broken because there were no more issues left without buyng more optional parts....So I ran all new wires from the sender, power feed, and ground to the extra gauge which didn't work (as usual). I then, after rechecking voltages and resistances again, moved the ground from the gauge case to a gauge mounting screw and the circut worked fine. Then I substuted the rally cluster into the circut which didn't work (as usual) until I grounded the mounting screw again.

It seems semi odd there is no ground tab on the cluster itself to promote a good ground for the various other circuts and lights, which seem to work fine, while the temp gauge didn't. Virtually all other GM products I've seen have one. This gauge case is isolated electrically so grounding the case does nothing. Ground has to make contact between the non insulated mounting bolt and the cluster, then from the cluster to the chassis and battery. I added a tab to the cluster for a push on connector and a 14 gauge ground wire to the rally cluster loom which grounds at the steering column support to firewall mounting bolt. Then I pulled out all my new temporary wires and reconnected the OEM looms which worked fine.

The vehicles green wire was good all the time. Now to pick a sender that has the right calibration value and I'll be good for another 35 years.

Thanks for your help and second opinions. Ladd.

[Brandon]

Way to go Lfowler! 8)

It never occurred to me that the gauge itself would have a faulty ground. Thanks for the update!

[Lfowler]

Yes that was someting I'd not come across either in exactly that way.

I noticed your log in has a big "ci" number. Are you running a larger than 455 engine? How do you get that big?

I've been thinking of building a larger than usual engine but are years behind on current Pontiac parts combinations. I've done several Ford and Chevrolet strokers with good success and have a machine shop so actual fabrication would be straightforward once I had a direction. Any advise? Ladd

[GPModJ]

Whooo--hoo! There are lots 'a new Pontiac parts available now. The only needed stuff we Ponti-Yackers are looking for is a good forged crankshaft or two.

Based on factory Pontiac blocks, you can easily build an engine as big as 474 cid. Lots of guys are running 46x engines--including myself. All you need is an Eagle cast stroker crank (4.25" stroke) and a bore of 4.185, which is completely do-able.

If you want something more expensive, you can go with one of the new Indian Adventures cast iron blocks and build something just over 600 cid--provided you don't mind paying for a billet crank. It'll take a crank with a 4.75" stroke and you can bore 'em out to around 4.375 to 4.4".

You can even build a big inch Poncho using an aluminum block. Jim Butler came out with an aluminum block just recently. If I recall correctly, the Butlers just used this aluminun block to build a dual turbo Poncho engine that put out close to 2,900 HP!

There are also a new set of aluminum D port heads done by Kaufmann Racing Equipment. There are reported to be another one or two designs on the way (we're told before the end of the year). One set is supposed to flow 400 CFM out of the box--but of course that's just hot air until it actually happens.

[Brandon]

Hi Ladd,

I'm running the Eagle stroker crank that GPModJ mentioned, in my 400 block. Dave Bisschop of SD Performance did my engine. One problem that some of the Eagle cranks have had is a coarse finish on the thrust surface, so that is something you'll want to check.

Thor mentioned a new book by Jim Hand - I'd check that out.

That's cool that you can do the work yourself. Good luck!

[Lfowler]

Do you have an opinion on the best "stock block" to start from? I'd like to keep my origional block / modified engine intact, or not at further risk, as it matches the chassie. Back in the 60's I remember many times hearing stock rod Pontiacs were bombs waiting to go off. I autocrossed mine for 3 seasons and hit 6500 -7000 RPM fairly often plus several flat out runs across the Utah / Nevada deserts ( once down the Salt Flats track) and CA hwy 5 Oregon to L.A. which has me real uneasy about further use of that rotating assembly.

I had a chance to buy some used Armasteel ? Forged OEM rods a couple of years ago but the fellow wanted $1000.00 for the set so I passed thinking there might be a better deal somewhere else.

The aluminum block is too expensive a part, I'd guess, for me despite my desire for it.

Thoughts?

[GPModJ]

A lot of people are running the Eagle "H" beam rods, which are pretty skookum. I've seen those rods run in applications up to about 1,000 HP. If the engine's going to see some high RPMs, go with some better bolts than come standard with the rods. I've got ARP 2000 bolts in mine--though my application won't ever see north of 7,000.

That said, I'm not sure the stock Pontiac rods are "bombs" waiting to go off--unless the engine will regularly see high RPMs. $1,000 for Armasteel rods? I think you'd be paying for cool factor there.

I've heard that pretty much any pre-74 block will do well but I've seen a lot of people express a preference for 455 blocks. Dave Bisschop suggested going with a 400 block because they're relatively plentiful and have 3" mains, rather than the 3.25" mains.

If you can afford the Indian Adventures block, they're bulletproof.

[Lfowler]

Hi Brandon and GPMod3,
I've used the Eagle rods in several Ford 347 strokers and Chev. applications without problems. I heard a rambling comment from Dema Elgin one time at dinner expressing dynamic loading theorys unfavorable to that design when he was discussing Cup camshaft designs but never followed up on that part of our conversation. They seem to work fine at the modest power levels my engines are built to produce.
Bolts are an interesting subject. Two years ago Joe Mondello went on for quite awhile about failures related to tightening, lack of fillet radius allowance, and surface finish of the bolt hole after removal of a stock bolt or replacement of a high performance bolt at the Superflow conference. (I buy those conference tapes every year and pick up interesting bits from the presenters.) Joe was quite passionate about those opinions when I talked to him several month later. I haven't had any rod failures related to clamping or bolt failures but don't want to start either. I changed my rod prep procedures to more closely follow Grumpy Jenkins thoughts about fifteen years ago and added a couple of Joe's methods since then. I'm still making up my mind about the overall costs of changing to stronger bolts which adds at least 4 hours to the rod reconditioning process plus triples assembly time when using a stretch gauge or just paying a few hundred more for lighter pistons and pulling 15 - 20 grams off the little end recprocating rod weight for a net reduction of 40 - 60 grams. I really like the light weight parts.

I just finished a 360 cid Chev in a 327 block using a big journal crank ground down to small journal sizes then stroked, then lightened. Don't know if that engine gained anything from the journal sizes because it is a mild hot rod deal but it was interesting to do and gains RPM quickly. No reason not to do the same on a Pontiac as long as the oil holes don't move sideways too much.

Thanks for your input. I think I'll start looking into 400 vs 455 stock blocks later in the year and after I get my interior finished. Is anyone going to the Pontiac Nationals in Tahoe? I have a couple of customers who want to take their older cars (1930's 40's) up so we've been getting them ready. I'll likely go and take my car as well but just for a fun drive. There is too much generic GM and home built in it to be a show car.

[Icelander]

Lfowler,

Good to see someone from my old stomping grounds posting way up here in the Northwest!

I hang around the Pontiac Street Performance site as well as play here and recall seeing a bit of a debate go on amongst some of the preofessional builders on that site regarding stock rods. (sorry for the run-on sentence)

To quickly summarize:
Many felt that the stock rods were good enough for less than 5000 RPM use. Almost everybody felt that since the price for the H-beam rods had dropped there was no real reason to spend money and energy reconditioning the stock rods (shot-peening etc.) since they've had 30+ years of rotation on them as opposed to the new H-beams.

When I get to that point, I will spend the extra dough and buy new rods. No sense in sweating a $500 detail.

To where abouts are you located? I periodically get down to visit old friends in the Fremont/Milpitas/Sunnyvale area.

Kendall

[Lfowler]

I guess this thread is long gone off the electrical topic but fun anyway.

My opinions are the same about rods. Fixing up a stock rod is a labor of love not necessity.

I'm in Santa Clara. Or rather the machine shop is there and I live in Mtn. View, a town or two further north. Give a shout and drop in. I'm in and out quite a bit all the time but never for very long (a few days is generally max.) Direct E mail and phone is on the web site. www.fowlerautomotive.com . My daughter is doing graduate work at Willammette in Salem OR. so I get up there several time a year but thats only half way to Washington, more or less, so dropping in at your clubs cruse in monthly events would be tough.

this club's web site has some really nice features and participants. I like the notification of a reply feature. Regards Ladd.

[GPModJ]

Lfowler:

Man, you just get to a place where you think you know the tiniest bit about engines and someone comes along with stuff you'd never considered. :shock: I guess that's what keeps it interesting. :D

Regarding Tahoe, that's something I'd like to do one of these days but higher on my agenda is simply making it to Seattle for Legends meeting and / or event. I'm not sure I'll ever get really serious about car shows after watching some of the guys with high-dollar cars. They're almost always trailered in. They're so meticulously maintained it's amazing but I can't imagine having to invest so much of myself in my car it makes it harder to simply drive. I just enjoy being there and participating. 8)

[Lfowler]

I understand what your saying. I've followed engine building for almost 40 years and still learn things quite often or get puzzled about why something happened.
I've worked on customers cars about the same length of time, a bit less, and noticed the guys having the most fun over all are the ones who can drive their vehicles whenever they want to. It doesn't seem to matter much if it's a high dollar car or boat or a modest effort. It seems to be the use and association and process which is the reward. Storing and hording parts or prep'ing for shows and show judging arguments get pretty tense more often than not.

It is a rare owner who can be a fun loving gentleman (or woman) when a half million dollar or up vehicle and best of show are on the line. It is a real treat when I can work for that sort of person, which happens a few times a year. The trick is to be sure they have fun so I can have fun too.

My personal projects are far more modest. It's been really hard to stand on the other side of the counter (so to speak) and lay down my cash for parts I need that I'd buy for a customer in a heartbeat. Guess thats why my GTO has been a couple of months away from being done for 15 years. However it is time I changed my life a bit to enjoy the shows and participate in the first person. So for better or worse I'm trying to get out of the shop a few days a week or do my projects on a regular basis and sell parts that I'll never use to clean out the garages. I've been on this track for about two years and it feels good.

I was a charter member of the Redwood Indian Chapter of the POIC 20? years ago and had some fun with them but faded out of association after a year or two to work more hours and get the shops going. Guess that club is gone now so the Tahoe meet will be the first Pontiac meet I've attended for a long time.

Perhaps I'll drive my car, certanily go with a friend or two, put an extra day on each end of the trip and a couple of stops along the way. Sounds fun hun? Maybe meet some old friends who's names I've long forgotten? This could be good. I'm really looking forward to it.

[GPModJ]

It's easy to understand how you can get wrapped up in something you enjoy and, as a result, spend all your time doing it. On the other hand, it really is the "office" and, as someone much wiser than me once said, "no one ever looked back on their life at the end of it and said 'gee, I wish I'd spent more time in the office.'"

I hope you enjoy Tahoe and all the cool Pontiacs you'll see there. Have fun and kick a tire or two for me.

[THOR]

I found myself in this hobby due to a longstanding appreciation of cool, fast cars. Early experiences in other people's Pontiacs and old memories of GTOs kicking butt in street races around the Bay Area had me in the Pontiac camp all along. I finally got a GTO and absolutely love it.

The thing that sticks in my mind the most, beyond the power, sound, and feel of going through the gears like a maniac, is how appreciative I am of all the friends and acquaintances I've made while owning this car and being associated with other folks into the same thing. GTO guys/gals are the greatest bunch of folks around. I'm glad to be part of this group. Thanks all :mrgreen:

[Lfowler]

Thanks, I will. Ladd