How do these plugs look to you? (image)
 

I'm diagnosing a cooling problem I've had for a while. I keep losing coolant, and I can't find a leak. Obviously, my first thought based on that is that I have a blown head gasket, or possibly a cracked head and the coolant is getting into the combustion chamber. I have no evidence of coolant in my oil, or oil in my coolant. So today I pulled my plugs to see what they looked like. I took a pic. They look pretty much the same to me, though there is some slight variation (as expected). The plugs are all almost the same color, however, the two rear plugs on the driver's side are darker than the rest (bottom middle and right in picture). The middle one on the driver's side (bottom middle) is slightly glazed. The passenger side rear plug was a bit lighter than the rest (upper right).

All, in all though, I think they show no sign of any problems. However, I can't understand why the threads on all of them would be rusty.

http://www.yippee38.net/images/Boxster/plugs.png

What do you guys think?

Plugs look fine. To track down the coolant, leak,pressure test the system with the spark plugs out. Listen for air at each plug, at the intake and at the tailpipe. If the headgasket is blown or if there is a crack in the head, you should be able to hear it.

If everything checks out,then put dye in the coolant and check for leaks in all the hoses with a UV light.

If you suspect a coolant leak, warm the engine and then run a proper leak down test on each cylinder. If you have a head or head gasket issue, it will show up in the numbers. I would also follow san rensho's lead and consider adding UV dye to the cooling system, it will leave a trace where ever the coolant is going.

Thanks guys. I'm glad to plugs look good.

Unfortunately, I don't have the equipment to do a leak down test, or a pressure test.

Ran compression. Got ~155 psi on the drivers side, and on the rear plug on the passenger side. Got 120-125 on the front two on that side.

The car's going in to the shop next week. Gonna have them diagnose it. I'm sick of dealing with it (been dealing with this problem for two years now).

I don't know how much coolant you're losing but my car has been losing about a 1-2 cups of coolant every month or so. Not a lot, but certainly enough to notice on the coolant tank and require topping it up to the max level before heading out to the track every few weeks.

My local indy says that the water pump has a leak/seep and the coolant evaporates rather than dripping on the ground (I never see any drips under the car). I have been holding off doing the repair until a after the holidays (and when I can get a break in my track schedule).

Since receiving this diagnosis, I will admit that I've been too lazy to get under the car and inspect the water pump for myself to see if there is any evidence to substantiate the claim of a leak/seep. I am planning to replace all 6 coil packs this weekend (12 yrs old, visible cracks, seem to be working ok but replacing to avoid any CEL's/problems) so I'll take a look at the water pump then.

Mike, when I took out my spark plugs they looked exactly the same, sans the fact they were BERU brand plugs. What thstone said can be very likely be a cause. If you can't find a leak you may want to check the radiators- it is very hard to diagnose unless you take the bumper/wheel well off. I had a small leak remedied by tightening a radiator clamp. Check the area where the coolant hose connects to the plastic radiator inlets and see if you can see any coolant around the area. What happens is that coolant leaks out slowly, but you will never see it, because it drips into the bumper/wheel well.

Like I said, I've been trying to diagnose this problem for two years. I started by replacing the coolant cap, then I replaced the reservoir. I noticed a small leak in the water pump (saw a drip coming from under the pulley), so I replaced that. Then I had a small "Y" hose blow out on me on the way to work. Replaced that and all hose clamps besides the ones on the reservoir since they're really tough to reach. When I was changing that "Y" hose, I noticed that my two main hoses looked swelled, so I replaced them. Somewhere along the way, I removed the bumper and checked the radiators for leaks, and found none. I cleaned them out though.

Yesterday, while under the car, I noticed a small drip of coolant on the engine end of the main hose on the driver side. That hose also looks swollen again, though the passenger side looks fine.

On the 29th, I got in the car to go by my parents' house. Backed it out and got about 4 houses away before I got a flashing CEL. I put the clutch in to stop, and the engine died. I started it again, turned around and drove the 4 houses back to my garage. It ran rough. The CEL code was a misfire on #5. This moring I tried to drive it again, and the same thing happened. I haven't checked the code, but if it is #5 again, I'm going to swap out coil packs and run it again to see if the misfire moves. If it does, I have to order some new coil packs. I called the local stealerships. They want between $118 and $175 EACH! PelicanParts is charging $35 each. I'll update if I have time to work on it today (working on my wife's truck today <sigh>).

Mike, the fact that you have low pressure on two adjacent cylinders indicates a bad headgasket or a (?) crack in the head. I would double check the compression and confirm with a leakdown test.

Yeah. That's what I was thinking San Rensho.