Technical Lets talk temp gauge theory

Sorry guys. No shop time for the past month. I have had 2 college graduates, 1 wedding and I moved my oldest to Phoenix. Just got back last night.

The engine is a stock Vortec, I do have a #6 line bypass line. I used the extra port on the water pump to circulate through the intake.

I plan on getting it swapped out tomorrow.

 

OK, so I added the spring in the lower hose, drove it about 15-20 miles and I thought it was golden....then all of a sudden it jumped to 250 degrees, I pulled into the shop, popped the cap and checked the water temp, it was reading about 180 with a manual gauge. I used a meat thermometer type. I added about 2 qts of water, put the cap back on and drove it the same distance. No problem the second time around.

I am still skeptical. I think it may reappear. I am wondering if it is an indication problem only. The spring did help keep the lower hose in shape. I am going to drive it some more for troubleshooting. I could change the thermostat just for giggles, but that doesn't make sense to me. It's only $6, but it's the hassle of draining everything etc.

 

So, I took it back out and drove it about 5 miles and it started pegging the gauge. It never acts hot and the temp gun shows normal. What would cause a gauge to work normally for a while and then gradually creep up? I may just have to slave in a second gauge to see what is going on.

 

Yeah, I hate to. I don't think I can match the one I have.
http://www.speedwaymotors.com/Omega-Kustom-5-Gauge-Set-Timeless-Tan-3-3-8-Electric,34403.html

 

Put a new gauge that matched the kit in it today. No change. Letting it cool down to see what a mechanical gauge will read. Very frustrated....

 

I have trouble with the mechanical gauges, (from time to time) My good S/W mechanical went out last year, young wife bought me a whole set of Classic Auto Meter gauges...(for when she rewires the truck)
She rewired my friend's identical '55 F100, beautiful job. Good planning, etc...

To bide my time, (and have a working temp gauge) I installed a Pep Boys Sunco mechanical. (looks just like the S/Ws, O.K. until wife Joey gets time to do the whole thing)
2 months ago, I'm on my way North to pick up a '36 axle, WHAT??? NO temp, needle is at rest on 100. (bottom number)
I swear, this will be the third mechanical temp gauge! I think my Auto Meters are all electric. (temp, fuel & oil pressure)
Never had problems with mechanical capillary tubes or gauges in the '50s, '60s, '70s. Just 'lately'!

Can a mechanical temp gauge be fixed in a general shop? (what's inside a capillary tube???) Yeah. Google.

 

This makes no sense. Drove 10 miles it creeps up to 200, which is where it should be, then all of a sudden it starts up to 250-260 in less than 10 seconds. It's like clockwork. Same distance every time. What happens at 10 miles? It went 650 miles before I ever had a problem. Now, it won't go away.

 

You mentioned above that you have your electric fan sensor in the head port. If the engine is really running as hot as the gauge says the fan would stay on constantly. I know you said the sensor is new but even so try measureing resistance on the gauge senser both when it's reading hot and cold and compair the readings to the gauge requirements. That would tell you is the sensor is doing it's thing or the gauge in just not processing correctly.

 

Have you checked the sending unit? You can test to 212 degrees with boiling water and an ohm meter, after that, would be best to use a propane torch on it while checking the resistance...one lead where the wire goes, other lead on the threads to complete the path.

 

I have a mechanical temp Guage in a pod on the frame with the thermostat knob for setting the electric fan. Since I can't see the Guage, I depend on the motometer as that gets your attention quicker that a Guage! Upper and lower hoses are actually stainless steel tubing with rubber connectors so they can't collapse

 

So I set up a small lab using my wifes cooking utensils. The sender was a replacement from Speedway. They wouldn't tell me what the original application was for. The range on the sender was 450 ohms cold to 29.6 at 250 degrees.



I checked it at 200 degrees which should have been in the 64 ohms range and it was all over the place from 25 down to 9 after it got heat soaked. I think the replacement is junk. It may be that they have the wrong senders paired up with the gauges.

I need a source to get this sender locally. I don't want another one from Speedway. My local parts guy spent 30 minutes trying to figure out what sender has this range, but no luck.

 

How's that radiator? Lippy

 

Brand new Walker. It's great. Temp gun shows it at around 170.

 

This the reason I choose to run early 70's or older Stewart warner (mech and electric w/nos Stewart warner sending units) or nos stock gauges. I've had too many new gauges/sending units (all different brands) go south. I guess the worst case you could get close with a quality sending unit and add resistors to bring it into line.

 

Yes the capillary tube can be fixed, Nads did a good tech here a few years ago and yes Google has the info.

 

No. I didn't see the need. I may send my new gauge back and tell them to send me a mechanical.

 

Dunno, I spent a couple days playing phone tag with Speedway and they ended up giving me credit on the gauge and sent me another sender....#3. They don't make a mechanical gauge in this series, so I figure I'll try the sender one more time. I changed it and it has been raining here for the last few days. Planning on driving it tomorrow.

 

Side note: I've used an infrared gun on my heads and water necks quite a bit (ford flattie). It always shows 20F or so lower than my (tested in boiling water) mechanical dash gauge. Coolant itself that much hotter than surrounding metal, I suppose.

 

Yeah, I take a collective average. I shoot the upper and lower hoses, the thermostat housing, the radiator etc.

 

Have you tried a gauge repair shop? They might be able to get the proper sending unit or modify your existing gauge to operate with a quality sending unit. I used Bob's speedometer here in Michigan they have been helpful in the past for me.

 

So time for an update. After 3 temp senders, 2 thermostats and a mechanical gauge install, the problem persists. After installing the autometer mechanical gauge, now I can see the temp surging. It surges from 195-260 in under 20 seconds.

I thought I might have induced it by the installation of the bypass line I fabbed up going from the front of the intake to the to of the water pump, so I removed that yesterday and that seemed to fix it. I drove it over 100 miles yesterday and 10 miles from my house it started back up! It ran 195-200 all day.

I am wondering if the impeller on this HV Flow Kooler water pump is slipping? It seems to rear it's head above 2,000 rpm out on the highway.

 

Found this. Gonna try this first. From Edelbrocks website:

SPECIAL NOTE: This intake manifold is primarily intended for use with Vortec heads on pre-Vortec blocks. 1995 and earlier blocks have the thermostat bypass water passage from the block directly to the water pump through the passenger side water pump mounting flange. If the manifold is used on a 1996 and later Vortec engine that does not have the in-block bypass passage, you must route a thermostat bypass hose from the water bypass port on the front of the manifold to the 5/8” hose nipple on the passenger side of the water pump. The 3/8” pipe to 5/8” hose nipple fitting, hose, and hose clamps are included in the kit. If your engine block has the thermostat bypass passage, use a 3/8” NPT plug supplied in the kit to plug the bypass port in the front of the intake manifold.

 

I added a T to the heater hose and ran a 5/8" nipple fitting on the front of the intake. That cured it. I did almost 300 miles yesterday and it was rock solid at 185. The problem is that we transferred the setup off of the 327 with Vortec heads. My bypass setup was correct for that setup. When I transferred it to the GM Vortec crate engine, that's when the problem started. Anyway, finally solved.