I have an L03, pretty much stock. I have the stock thermostat (no idea how old). My fan works, and i have it setup with a toggle switch so i know it's on when that switch is turned on.

Now, the problem i'm having is, is that sometimes my coolant temp will rise >260, sometimes it will stay around 200, sometimes it will stay at around 200 then pop down to 180 real quick, then slowly climb to 200 again and do it again. The fan is on the entire time this is occuring. The engine doesn't seem to change it's sound or behave differently. When the temp rises uncontrollably, turning the defrost on full brings it back down.

Now, none of that happens all the time, it's sort of random with the majority of the time it just sits at around the middle straight up.

I'm thinking it's a stuck/clogged/crapped out thermostat. But i was wondering if anyone else had any experience with this behavior and what they did to fix it. Rust is no stranger to my coolant system.


ps. What the hell is the temp sensor reading when it's showing a temp > 260? I have likely a slightly high ratio of antifreeze to water in my coolant, but i didn't think it would still have a boiling temp > 260 degrees.

 

Sounds like a blown head gasket. Is coolant disappearing with no apparent leaks? Does your car puff a little white smoke when you first start it? Steam pockets can form from the pulsations caused by the compression leaking into the water jacket. This makes the temp gauge say unbelievable things.

 

I'm not sure really if the coolant is leaking into the engine. I should see evidence of it in the oil and I never have before, (and this problem has been going on for a long while now). I'll check again today. My coolant gets dirty looking, but like i said, my coolant system is rusted to crap. It doesn't really look like there is oil in it though. It's been a couple months since i flushed the coolant and put new in and filled it up. It's still pretty full. I'm not exactly sure what level i filled it to though, my resevoir bottle is dirty as hell inside it and i can't get it clean. (time for a new one i guess).

I dont really get any exhaust smoke at all, white,black or otherwise. I havn't driven the car in over a month, so i'll pay more attention when i get off work today and see what it does when i start it up.

Steam pockets seem like i would get periods of high temp then it would go down on it's own when the steam pocket passed. The behavior i'm seeing seems almost like the something is periodically blocking my thermostat.

Also, when i flushed my coolant, i noticed that even when i was up to temp, my coolant flow would just stop for a bit, then continue. RPM and engine noise didn't change, the coolant would be flowing strong out of the radiator and then suddenly just stop for about 10-15 seconds or so and then start back up again.

edit: also the temp during normal running is at the middle mark (when it's actually working like it should). A year or two ago it would always sit a decent amount to the left of the middle mark. Now it seems like it never gets that cool.

I'd just take the water neck off and check the thermostat today, but i'm not so sure my apartment complex will appreciate coolant all over the place.

 

You won't necessarily get water in the oil or oil into the water. There can be a leak between the cylinder and water jacket passage thru the gasket. The engine will run fine, but it will slowly lose coolant.

 

is it the stock temp guage? i have little to no faith in the stock gauges, especially with the description of "erratic changes." i would say that the coolent temp shouldnt be erratic or move really quickly unless you have some serious issues (head gasket, etc.)

i would do a compression test on all cylinders, if you see two consecutive cylinders with significantly lower psi, it is likely a headgasket or cracked head.

is it smoking at all? losing coolent?

to see if the coolent is mixing with the oil, i would pick up a test for the coolent that determines the amount of hydrocarbons (or another component of oil, i cant remember which for sure), if it shows that there are some traces of oil, then you know you have issues somewhere.

at least head gaskets are easy on third gens. i did one on my 4.6L mustang and man it sucked, compared to the SBC's.

 

Well, i'm likely going to replace the thermostat first, since it costs basically nothing. If that doesn't solve the issue, then i'll have to look into replacing the head gasket. How much does replacing the head gasket usually cost if nothing else is really damaged? Basically, how many hours does it take a mechanic to replace it?

I crossing my fingers on the thermostat being rusted to crap. I had chunks of crap coming out when i flushed the system, I would not be surprised if big pieces of rust got clogged in the thermostat.

 

Something tells me that the sporadic flow stopping when i was flushing the coolant is important to this problem. Basically, the flow was not consistent out of the radiator. It would be flowing really strong (water pump working good) then it would seem restricted, then it would either nearly stop altogether or go back to being strong again. I was using the normal flushing kit you find at autozone/pepboys/etc. I've got no idea if it bypasses the thermostat, but i would think that it would have to since after a while the coolant temp goes extremely low when flushing. If it does bypass the T-stat, then what could be causing this change in flow-rate? Something stuck in the radiator itself? The temp responds well to turning the defrost on, i'm not sure how that changes the coolant flow path other than diverting some to the heater core, but whatever it does seems to get around my problem. The fans are on and this happens even at speed.

I'm not going to rule out headgasket, it wouldn't surprise me, since everything that can go wrong with this damn car does. But, this has been happening for a long time now, and i'm not sure how the flow issue during flushing fits in with a head gasket problem.

 

The change in flow while flushing is normal. It is a result of the t-stat opening and closing-the flow can't bypass it, the hose from the top of the rad must go thru the t-stat.

Erratic action of the temp guage is usually the result of a bad temp guage. The best way to check is to borrow a scan tool and compare your dash guage readings to the scan tool readings.

I would think it highly unlikely that a blown headgasket would cause this problem WITHOUT any other obvious symptoms. There are many other possible causes I'd investigate before even doing a compression test-which is a must before assuming a head gasket. I've even seen EST problems affecting spark timing and cause random overheating problems.

 

"""Erratic action of the temp guage is usually the result of a bad temp guage. The best way to check is to borrow a scan tool and compare your dash guage readings to the scan tool readings.""


i totally agree (i stated that earlier if i remember correctly). honestly i would look at it when the gauge said 260* and if you can touch the hose at all, the gauge is probably bad. i still have a hard time thinking it could really be 260* i think you would be having some major issues if it was.

definitely pick up a t-stat go for Stant (even if you dont need it immediately they are a good thing to replace periodically), and feel the hose when it is reading really high. i bet it is the gauge or sending unit.

 

Well, i changed out the thermostat. As i suspected, the old one was caked with orange crap from when I had dexcool in it. Plus, it seemed rusted as it was quite hard to compress the spring. I put a new 180 degree thermostat in and it was keeping cool like a champ. Better than it's ever done before. I waited until the temp got up to 220 and then turned my fan on. The temp went right down to ~180.

So, it looks like i dodged a bullet.

 

The same thing happend to me. I flushed out the dexcool until I got it out and the water came out cloudy. Then i popped in a Stant 180 Therm. Filled up the car with Prestone and water. There was good flow at the ratiador once the thermostat opened up but then the temp guage showed 260. I too turned on the A/C which kicked the fan on and brought the temp back to 180. I'm guessing, the dexcool ruined the temp sensors.