[blacksunshine400]

For years my 78 formula 400 had no functioning water temp gauge. Last season, I had a local rad shop flush and fill the system. They discovered that there was no thermostat present, and that the cap did not seal properly. They installed (what i just discovered) was a 195 degree stat, and a new cap. Ignorance is bliss and I happily drove the car the rest of the season. Late in the season I falsely diagnosed a bad head gasket and in a moment of panic, bypassed the heater core and dumped a can of bars leaks head gasket fix in the rad and hoped for the best. It didn't work, and I stored the car, for I had bigger fish to fry. I'm a carpenter, not a mechanic folks, but I'm learning.

This spring, I learned that my head gasket was fine, and the source of all my whiteish smoke was an improperly connected and functioning pcv valve. What a relief. With renewed vigor, I tackled the faulty water gauge. I found simply the wiring harness to be a little chewed up. Cleaned it up, plugged it in, and now I have oil pressure and water temp again. This brings me to my latest problem. The car (according to the gauge) gets up to about 240 and then comes down to around 220 and pretty much sits there. I did a little research and figured that my heater bypass was messing with the flow characteristics, so I blocked the two inlets on the pump and intake/cylinder head and took her for a rip. Even worse this time... gauge got all the way over to 260 just going around the block a couple times.

I've done a little prep work this evening. Drained the rad and flushed it with the hose. Reverse flushed the motor with the hose. Pulled the 195 stat and put in a 160 that I had new in the box and swapped the temp sending unit in the cylinder head for a known good one.

That 195 stat seemed a little gunked up at the top when I pulled it out. I'll fill up the coolant tomorrow eve after work. I don't want to do it tonight because of the RTV on the stat housing.

Could that bars leaks crap have gunked up my thermostat causing it to stick like that?
Does a gauge that has failed still read anything? Who's got money on the sending unit? It's at least 15 years old. I know that.

All help appreciated.

[Pontirag]

A rule of thumb is that

white smoke means your burning antifreeze,(antifreeze is leaking into the combustion chamber)

Blue smoke means your burning oil ( your engine is worn, or seals are bad from sitting)

black smoke means your burning gas ( carb is running rich)

white smoke would not be caused by a PCV valve,White smoke would be coolant. If it was the PCV valve it would be blue smoke. when you pulled the pcv valve was it all slimey with a whitish or brownish creamy looking slime? That would suggest water in the oil.

Not sure what you mean when you say the thermostat is all gunked up.

typically if there is white or creamy looking slim on the cap or in the system then oil is getting into the system

the sending unit is usually pretty reliable even with age, but what can skew the read out is resistance caused by a bad ground.

flushing the system: what came out? rust? slimy gunk?

Over all there are no easy answers, when cars get this old, and have high milage and or sit for extended time it couls be any combination of several emerging problems.

a systematic evaluation of each component and its condition must be made. and since these cars are old often as not parts must be replaced.

read some of the posts that others have made. they will help in diagnosing the problem.

[blacksunshine400]

Head gaskets are fine. Oil is clean, coolant is clean. Smoke is gone. Not the topic of discussion but thanks for the concern. Coolant flushed from rad and motor were clean. Stat had a little gunk and varnishing on it. I think it was beginning to fail. All will be revealed tomorrow.

My theory is that the bars leaks is designed to seal leaks. There were no leaks so perhaps some of it was held up at the stat before it opened

[Squidward]

You started at a good place, the t-stat. It is easy and cheap.

Another thing to check: There is lots of discussion on here about divider plates, discussed to infinity and stickied at the top. I'm not saying to yank the pump at this time, but you can look down where your water pump meets your timing cover, and should see a steel plate sandwiched in between the timing cover and pump.

I don't know how long you've had the car or if you are a long time Pontiac guy, but you can't assume that the divider plate was inserted the last time a water pump was installed. I know this because I got scalded pretty good once by an overheating engine that had just had the WP replaced before I bought it - receipt was with the car. After going through the usual (radiator, t-stats, etc) I pulled the pump and it had no plate.

If you get to the point of pulling the pump, see the stickied divider plate topic on getting good clearance. Another issue to check is to make sure that your timing cover coolant sleeves have the rubber sealing rings that mate up against the two smaller holes in the divider plate. These get brittle and fall apart with heat and time, and if degraded will allow water flow to bypass from the discharge of the pump (the two water sleeves) back to the suction (the big middle hole in the divider plate).

Does your engine fan spin up properly and move a good deal of air?

[Pontirag]

also the devider plate can rust away too and I have seen timing chain covers that were very badly corroded. in these cases I removed freeze plugs and found rust scales in the bottom of the engine block almost 2 inches deep.

Overheating can also becaused by ignition problems like very loose timing chains and badly worn or rusty cintrifigal weights under the rotor. these two problems usually go hand in hand with each other

[blacksunshine400]

Thanks guys. Gotta work today. Will fill up the system and test this evening.

[blacksunshine400]

Yesterday turned into today. System seems to be functioning properly, but gauge still reads too hot. I installed the 160 stat and drilled two 1/8" holes in it. Gauge reads over 220 when the stat opens and starts to flow coolant. Seems my old sending unit was functioning properly. I am going to test the gauge by placing the old sending unit in some boiling water and see what the gauge does.

[blacksunshine400]

I think I have traced the problem to a weak ground in the dash. I tested the new sender with an ohms meter. I obtained the info on the sender from this

http://forums.highperformancepontiac...ion/index.html

When my gauge reads around 235 i'm getting 131 ohms at the sender unit, telling me it is much cooler than the 82 ohms at 220 that is listed. When I replace the sending unit wire, the gauge jumps to about 180 immediately (about right) and then slowly creeps up to 235ish.

What do you guys think? On the right track? I'm going to run a ground directly from the gauge to a good grounding point next.