Well I planned on doing bodywork this weekend, but my car had other plans. On the way home on the highway after lunch I noticed my temp gauge was 3/4 up and climbing, I pulled over immediately and turned the car off with the heat going. After waiting ~30 minutes I decided to limp home since my house was only 10 minutes away and I figured there was just a bubble in my cooling system as there were no visible leaks and I had been struggling with burping it after I replaced the alternator. I drove home, noticing the temp would rise at high revs but for the most part it would stay in the middle if I drove conservatively. At no point did the temp gauge hit the top, and when it began to climb again I pulled over and let it cool. At this point I noticed the lower radiator hose wasn't getting hot anymore.... but I was right down the street so I drove it home, for the last leg of the journey the gauge stayed right where it should be.

I parked it, turned it off, and 25 minutes later pulled it into the garage... So much for the rust repair.

5 hours later the car would crank and sputter but not start.

Is the VQ35 that delicate? .... I'll check compression as soon as I can but that won't be for at least a month. What are the odds I have two unrelated issues?
If I need a new engine, this might be the end of my time here, as I can't dedicate that much time or money to a swap right now, and I'm not going to pay a shop $3000 to put a new engine, clutch, and flywheel into my rusty G.

 

Check your coolant for oil or your oil for coolant.

 

Pull and inspect your spark plugs, use a flashlight to look inside each cylinder for Stuff™. If you have access to a borescope it's much easier.

I would also turn the engine by hand once the spark plugs are out (battery disconnected, drive belts disconnected, socket in the crank pulley to turn) to move pistons to the bottom of the stroke because you can't see anything when they're at the top.

It can DEFINITELY be unrelated issues, don't assume, start troubleshooting.

 

Thanks for the moral support, when i posted i was kinda freaking out lol. Everyone IRL (at home) was telling me that this is what happens when you work on your own car without mechanic training.

Today it was much warmer, and the engine started up after a second or two of cranking and settled down into a steady idle after struggling for a moment. This behavior was consistent after several starts.

I drove it up and down the street but it seems fine, even revving to 4k... No codes. There's no oil in my coolant and no smoke out the exhaust. Coolant is filled to the top of the radiator just like i left it.

Headed back to school for the next month but will pull plugs, check compression, check for air leaks, and visually check inside cylinders later in October.

As for the fluctuating temp gauge, am i correct in diagnosing the thermostat given i have heat at idle, fans operate properly, lower rad hose is colder than the upper, and no leaks? Honestly i should have thrown a 15 dollar thermostat at it last coolant flush, but live and learn...

 

$10 bucks says it's a thermostat. The lower hose is typically noticeably cooler than the upper in my car. If the thermo doesn't fix it, it's probably the water pump.

 

I recommend buying a cheapo infrared heat gun, toss it in the glove box, next time you overheat pop the hood and shoot the upper and lower hoses, it's a hell of a lot easier with the IR gun and you can pick them up for under $15 on Amazon or harbor freight. I have a couple of this exact one which is great for most automotive use, range is -58°F to +768°F which is good for naturally aspirated vehicles. Make sure it has a laser pointer like the one I listed.

https://www.amazon.com/gp/aw/d/B00837ZGRY/ref=oh_aui_i_sh_in_o0_img?ie=UTF8&psc=1

 

Anyone ever had a bad temperature sensor and can speak to the symptoms? Found a thread on NICOclub where a guy was having similar hard starting issues where the motor would run fine once it did. That would also explain why when my engine "overheated" it didn't feel particularly hot in the engine bay and the gauge would start rising while cruising at a constant speed and then be fine again with no change in behavior.

The sensor is $6 for a Stant sensor so I'm going to just throw one at it for PM this weekend along with new t-stat, upper and lower coolant hoses (not that they have a problem, but I don't wanna have any cooling system problems because of a burst $5 hose).

Thoughts on changing the water pump/tensioner at 14 years old and 130k miles on a well maintained cooling system? Waste of time/money?

 

Personally when I have cooling issues I replace everything, water pump, radiator, hoses, thermostat. Especially if I was doing the repair on a 130k mile engine, if those are the stock components then they are definitely worn. Maybe not to the point of FAILURE but definitely getting near the end of the expected life of the component and I tend to replace an entire system when it fails.

 

Tensioner? I wouldn't change the water pump unless it's broken. If it ain't broke...unless of coarse it's something close to something you're repairing that was difficult to get to and now said 1st something is exposed, a typical future type repair and easy to replace due to replacing said 2nd something. Get it?

 

Hm, I just ordered new hoses, a coolant temperature sensor, and a new T-stat. Hopefully that deals with the problems. I'll probably replace my water pump as PM at some point but not this weekend when my car still has bare metal exposed on the quarter panels from the half done rust repair.

At least my parents let me leave it in the garage this time unlike when it's painted :P

 

Coolant temperature sensor would make sense. Only reason I think that is because of the hard start after you got the car home. Sensor might think the engine is hot or cold and giving a lean fuel/air mixture. Not something you hear about often
Since it's a sensor though shouldn't it throw a code?

 

I agree they don't go bad often and theoretically it should throw a code, but that's the ONE single component which COULD be responsible for both my "overheating" and the hard starting when cold other than the head gasket.... and it's $6 and sits right on top of the engine.

It could be two separate unrelated problems, but doesn't seem very likely that they'd both show up at exactly the same time with no warning beforehand for either issue. But just in case I'm also throwing a $15 Chinese aftermarket crankshaft sensor with good amazon reviews at it since that's the only engine sensor I haven't replaced preventatively.

I'll be keeping the functioning used OEM one in the trunk with my working used OE cam sensors, coil packs, and drive belt though just in case I get unlucky with the aftermarket parts roulette.

I'm still on my original O2 sensors, should I clean those while the Bondo is drying to make them last longer, or is it not worth the effort and I should just replace them when they throw codes?

 

UPDATE: Car is fixed, my hunch was correct!

Started the car when I got home, it took a few seconds to start and would change idle speeds just like before. Still no codes pending or otherwise. This time I noticed the temperature gauge would jump up and down slightly even seconds after the car started, reinforcing the idea the sensor was the problem.

Turned off engine, replaced coolant temperature sensor with a $6 Beck-Arnley part off RockAuto. Started right up and idled perfectly. Looks like it was never overheating in the first place, just a little confused!

Looks like this is a good cheap PM part to throw at the Gs as they age.

 

 

Great idea, I think I'm still on the OEM one so I'll add it to my dwindling list of components to change when I'm tearing into stuff next.

Glad everything worked out and it ended up being a simple and CHEAP fix.