a wierd gauge issue on 1994

[Marv D]

not sure wht the heck... Have a A-pillar guage set, sensor is in the intake beside the thermostat housing. It syats ROCK SOLID at 170°
BUT the dash temp gauge started making slow sweeps up to 250°+, sets the 'check gauges" lamp, then drops back to 170ish,

I replaced the factory temp sensor in the drivers side head (a 1 wire sensor ) ,,, does exactly the same thing. Unplug the sensor and gauge drops to 0,

With the pod gauge staying consistant,, I brought my Fluke certified temp gun,, and the thermostat housing is staying at 170 even if the dash gauge says 250, And I know the smell of a HOT motor (living in the Arizona desert) It's just not hot!

The sweep from 170 to 250 will take 30 seconds or so. I tried grounding the sensor wire and it flashes to PEGGED the dash gauge.

All of that to say I have to believe the motor is NOT getting hot unless there is some weird steam bubble happening at that sensor. But I'm not loosing coolant, no coolant in the oil, radiator is full (no bubbles)

is this a common issue?
Anyone have ot know of a gauge problem that may cause this. I have a guy that rebuilds 04-06 GM gauge pods when the resistors fail and they dont 'resert' But I can't get ahold of him.

Looking for insight

[sntrym95]

When I had my bypass line on the pass side and the gauge temp sending unit on the driver, I experienced a similar spike when the engine first warmed up. Once the tstat opened, mine sat right at 195.

I recently replaced the intake manifold with a dual plane square bore (with TBI adapter). This intake has outlets in each corner. Since the rear passenger outlet is used for the heater core, I setup the water pump bypass on the drivers side of the intake and no more spikes.

I should also add that I have a Vortec water pump and have plugged the bypass hole in the block. If you have a stock TBI motor, you won't have that option. Bottom line is the head does get hot before the tstat opens because of the flow restriction on the driver side.

[Marv D]

Thanks, but its not a 'warmup 'thermostat spike,, this just started a month ago and I built the RHS vortec head 383 roller motor for it like 9 years ago. Has never done this 'spike before.

I'm absolutely with you on the vortec heads and the stock 94 heater hose routing. I used a GMPP TBI intake and had it bored for the Holley throttle body. Finding a heater hose routing that does not bypass the thermostat is 'challenging' aint it!!

Guess I'll replace he thermostat even though the T-stat housing never even gets over 170 when the 'gauge' shows 240+

I'm just at a loss why it would 'sweep' to hot over 30 seconds, then sweep back to 170. A short to ground and it peggs isntantly, unplug it for open circuit and it goes to 0°

All I can come up with is all of a sudden ts developing steam pockets in the head at the sensor, or the gauge is just STUPID.

Oh wait,, heres an idea that should at least solve if it IS getting hot spots or not.... Maybe I'll put a mechanical gauge in the head in place of the sensor and just see WTH..

Does anybody know of a competant party to rebuild the 94 dash cluster and test the circuits and all???