I have a 1957 Chrysler 392 Hemi in my car. I've been running it for 16 years, and have never had a heating issue. This spring, the temp gauge has been spiking up to 245 degrees. It goes up and drops down quickly, which is su****ious because it has almost 6 gallons of coolant in it. The temp on that much coolant can't change this fast. It does the exact same thing whether it's 50 degrees or 90 degrees outside. From a cold start the temp rises normally to 195 degrees where the thermostat opens. After that it seems to be all over the place. The belt and water pump appear to be working fine, and I verified that the temp gauge is correct with a non contact laser thermometer on the water crossover. Even when it's "hot", the water crossover reads the same as the temp gauge. I put on a new standard 13 lb radiator cap. I bought a new thermostat, tested and verified that it was opening and closing at the right temp before installing, and it's still the same. The oil is clean, and the exhaust pipes are clean inside. No smoke or any other signs that anything might be wrong. No misses or misfires. If you weren't looking at the temp gauge, you would never know anything was wrong. It runs completely normal. I can't tell if there are any bubbles in the radiator because I can't see the coolant level from the filler neck. What do you think? Head gasket? Hot gas bubbles drifting across the temp sensor? I'm thinking that's all that is left. Ideas? Anyone else had this happen?
Sure sounds like something acting like a thermostat. Some sort if intermittent blockage. How are the hoses inside?
You're right. It looks exactly like a sticky thermostat. I'm on my third one, though... and I tested this one before I installed it. The lower hose has a steel spring inside to keep it from collapsing, but I didn't pull it to look inside. I probably should do that before I start to pull heads. That's a good idea, thank you.
Well..... This can be a inline six, a sbc, or a cammer ford for what matters..... You've done the t-stat deal. Now= manual or electric gauges? What about senders/gauges ****ting the bed? WE/I need a lil bit more info of the /your combo..... Manual is one thing- and can/should be checked/verified with another manual gauge... electric has a sender/gauge....... Even though it's been a good run- parts fail, and we need to diagnose..............
The gauge is mechanical. Once above 200 degrees, it changes temp so quickly that I suspected a possible gauge problem, too. I was told that they go bad all the time, but the gauge seems to read within 10 degrees of what the laser thermometer reads, so I figured it must be OK. I don't have another gauge to compare to, though. Do you think the non-contact laser thermometer is a reasonable verification, or should I bite the bullet and go buy another gauge? Thanks.
Top off the coolant and put a hose on the overflow tube with the end in a bucket of water. If it's a head gasket it will blow bubbles in the bucket. Does it have a clutch fan I had one that the temp gauge got almost to the red before it would lockup and then be OK.
The sender is at the middle top of the p***enger side cylinder head in the intake manifold. Under normal cir***stances, the gauge reads 180 in the cylinder head when the 195 degree thermostat opens in the crossover.
It has a mechanical non-clutch fan. The overflow tube into a bucket of water is a great idea, I hadn't thought of that either. Thank you.
OK, today I pulled the lower radiator hose and everything looked good. Clean as a whistle inside the radiator and the water pump. Since I had it apart anyway, I put a new hose on it. One more possible problem eliminated. I didn't get a chance to try the overflow hose in a bucket of water. I'll try that this week sometime.
We chased an overheating and erratic high temperature problem on a friends car only to find out the temperature sending unit had gone bad. Found it by putting a thermometer in the radiator with the cap off. Hope that is the same problem with yours. Also try one of those non contact temperature readers at different places on the radiator. KK
I used my non-contact laser thermometer on the cylinder head and water crossover, and it was within 10 degrees of what the gauge said. I may still try to borrow a different temp gauge from someone else, though. Other than the needle on the gauge, there are no other symptoms. None. That does make me wonder if I'm chasing shadows.
It has been running perfectly with a 195 degree thermostat for 16 years and 95,000 miles. If it was a fresh build and was unproved, I would give definitely that a try. There is a problem somewhere other than the thermostat, though. I think I'll be ordering a head gasket set tomorrow morning. At this point, it has to be either a flaky gauge or a leaky head gasket. I've ruled out everything else.
I had a similar problem on a SBC in a Model A that had a bubble of air in the cooling system. Bled that off and problem gone. It would spike scary high and then a minute or so later it would ease back down almost as quickly. Its hard to get my 10:1 392 much over 195 with a 190 thermostat.
That's what makes this so strange. For 16 years my temp gauge has been nothing but an ornament on the dash. I never needed to watch it because the engine never ran hot. I drilled two 1/8" air bleed holes in the thermostat skirt so any air would purge right out. That's just standard procedure for me, so I didn't think to mention it. Tomorrow morning I'll order a head gasket kit and just pull it all apart to make sure. Sent using Tapatalk from someplace deep inside the garage
This kit below will tell you if you have combustion gas in the coolant. At 95k it might be worth a look in there anyway. But I'd run this test , not because I have it sitting here which does make it easy. If you're suspecting air pockets - Pump cavitation can cause you erratic heating problems. That would be gradual too if it were an internal radiator problem of flow. You'd never see the hose **** flat because of the spring.
Sometimes the water pump impeller can break free from the shaft causing water to flow intermittently, also causing spikes in temperature.
Those kits work great went car buying with the grandson the first 3 cars we checked did not p***. You have got to love engines with aluminum heads that didn't have good cooling system maintenance
The 392 in my roadster has a 160 thermostat, it opens and then the temp drops to 150, the only time i turn on the electric fan is on an extremely hot day in bumper to bumper stop and go traffic. I had a 354 in a 36 years ago and never had a cooling problem.
I was going to mention the pump as well. The impellers rot off and get to the point that are stirring the water more then pumping it. 16 years is a long time.
The water pump is only 8 years old. The original one I put in when I built the engine had a leaky seal and was replaced. It is an aluminum Weiand high flow pump, and has worked flawlessly.
OK, I had it narrowed down to bad gauge or bad head gasket, so I went to O'Reilly's and bought a $25 mechanical temp gauge. My engine is NOT running hot. The old gauge is defective. Everyone who suggested bad gauge was correct. I have a trip planned in two weeks, and this had to be addressed before I felt comfortable driving it long distance. Thank you for all of your suggestions and helpful tips. You guys are the best.
Glad you got it fixed. Maybe the laser thermometer was also throwing you off? Reads the outside of the engine, not coolant temp. Hard to validate a Gauge reading with that method. Still, happy you are not the owner of a melting hemi
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