CrazyCutty72

I wasn't sure wether to put this in engine or electrical but I just wanted an opinion here. A couple months ago I was going for a ride on a hot day when I noticed my gauge spiked. I pulled over and noticed I blew my upper coolant hose. I had someone come bring me a new hose and more coolant. Ever since then I've had some issues. My aftermarket Bosch gauge will go up to my normal temperature of 190 for a little while and then spike up to 230 then drop back down within a couple seconds. It'll consistently do that over the course of a couple miles. Sometimes it'll go up to 250 and then back down. So I'm wonder if you guys think it's a faulty gauge or a more serious issue like a head gasket? It'll stay at 190 at idle. The thermostat was changed shortly before this issue and the 50/50 coolant is at the correct level. I believe I have all the air out of the system. It's a mechanical gauge and the sensor is in the intake right next to the thermostat which I know isn't a very accurate spot but it just worries me because I don't believe it did that before. Would it just be from the thermostat opening and closing? I believe I put a 185 in. I don't remember completely. I'm just perplexed because I didn't change anything else. Thanks for any input

jaunty75

A couple of comments.

First you "believe" you have all the are out of the system? How firmly do you believe this because it sure sounds like you have an air pocket that occasionally passes over the sensor, momentarily rendering it not in contact with the coolant. I recently replaced the radiator and coolant in my '67 Delta, and it did this temperature spike thing for a short while after I finished the job. I presumed it was an air pocket that resulted when I poured the coolant back in, and after a few short drives allowing the car to reach operating temperature, the problem went away.

I don't understand what you mean when you say that the sensor being next to the thermostat is not very accurate. Isn't that the factory location? Where else would you put it?

Tedd Thompson

I usually don't reply on the newer A body cars but if me I would check out the thermostat and also make sure all the air is out of the system. A sticky thermostat will act like that and new doesn't necessarily mean it's good. Air bubbles trapped in the block will also give those systems. If you hit 250 degrees or about your radiator cap should have opened up. Are you sure the gauge is working correctly?.... Tedd

oldcutlass

Rapid swings of the temp gauge means you have an air pocket as explained above. I usually run the engine to temp with the radiator cap off, put the nozzle of a water hose in the radiator neck at a slow flow and force the air out.

joe_padavano

^^^THIS! First, be REALLY sure you have all the air out. Second, if you believe there's a head gasket problem, run a leakdown test. Cast iron motors are much less likely to blow a head gasket when overheated than are aluminum motors.

CrazyCutty72

Well I let it run a couple times with the cap off and the radiator towards an uphill slope so I just assumed it's all out. And I was always told the best place for a temp gauge is the head like a Chevy because you'll get a more accurate reading than by the thermostat

CrazyCutty72

I just wasn't sure if this is vindictive of a head gasket problem. I was just worried to drive it because I didn't want to hurt anything. I'll try to get all the air out again and hope it fixes it. I just wanted to see if you guys thought it was air or any other suggestions. Two heads are better than one

joe_padavano

Likely you were told that by people who only ever worked on Chevys...

FYI, the Chevy temp sender location in the head is in the middle of the head and only "sees" the coolant part way through the motor. The Olds location at the coolant crossover in the front of the intake manifold is arguably the hottest location, since it is right before the coolant exits the motor to the radiator.

CrazyCutty72

The gauge worked before the hose so I figured it's working now. It did open a couple times when I first filled it but that's because I filled it to the cap and it spit out whatever it didn't want. I was just confused because the thermostat worked when I first put it in so I assume it should be fine yet. It seems like the general consensus is air so I'll go that route first before I fiddle with my chewed up thermostat housing on the intake. I had a heck of a time getting it to seal right

CrazyCutty72

Thanks for clearing that up.

Tedd Thompson

Just another thought, are you sure your radiator cap isn't leaking? the loss of pressure will cause a high temp spike. Very common for some reason in Miatas with ill fitting new caps..... Tedd

oldcutlass

The sender can be in each head (between 1 and 3 or 6 and 8 cylinders) or the intake manifold, the head usually reads 10-15* hotter than the manifold and will fluctuate more under load.