please diagnose my cooling prob.

My Sidekick is driving me crazy. The temperature is jumping all over the place. Here's the full history:

When my in-laws still had the truck, they had problems w/it overheating. After taking it to the local redneck mechanic several times unsuccesfully, they finally changed the radiator cap at my suggestion & it supposedly had been running fine.

They hadn't driven it much before they handed it over to me, and I had it in the garage for about 6-weeks fixing all the rust before I started driving it. In that time span, the right brake caliper siezed up, so I suppose(in theory, anyway)it's possible something went flakey with the cooling system also.

When I started driving it, the temp gauge would just barely move off "C" and would move up & down. The air out the heater was cold also.

I replaced the t-stat(I checked it in a pot of water before I installed it). I let it run to burp the air out of the system, but the lower hose never felt like it warmed up. Immediately after replacement, the gauge would come up a bit higher, about 1/3rd the way up & the heat was a bit warmer, but the gauge would still move around quite a bit, sometimes dropping almost all the way to "C", and sometimes climbing 2/3rds up the gauge.

Driving it the other night, the gauge climbed all the way to "H", and just as I came to a place to pull over, it dropped back down to 1/3rd. I kept going & it was fine for another 10min, then it happend again several times. I turned around and drove another 20mi home, but it didn't do it again the whole way back.

What the hell could be causing this? I suppose some type of blockage could cause the intermittent overheating, but to jump between hot & cold has me baffled. FWIW, my in-laws had the system pressure tested & everything is OK.

I had similiar issues after I bought my Miata. I went through the whole system piece by piece. Rad cap, T-stat, water pump, even flushed the system then finally radiator itself. That fixed it. Apparently the core was partially restricted.

Your description, particularly the paragraph where you describe it climbing to H and then dropping back down to 1/3 sounds a great deal like air trapping around the thermostat.

I do not know the Sidekick, and normally discount air stories and a bunch of hoey, but there are individual engines and chassis that are remarkably difficult to bleed. If, per chance this vehicle is one of them, do the oem proper drill to bleed it.

I agree. I've had plenty of VW's that were hard to bleed(the h2o cars... ), and the symptoms are very similar. On dubs, there's often some part of the system higher than the rad cap, but on the Kick the cap is the highest part of the system.

I suppose if there's a blockage, that could cause the bubbles. I hope it warms up enough this weekend to flush out the system.

foxtrapper is dead on the money. An air pocket will do exactly what you describe.

You might try this: get one of those inline flush fittings like this: Install it in the HIGHEST POINT! of the heater hoses and preferably above the top of the radiator, then fill in the normal way with the cap removed, wait for coolant to run out of the fitting then quickly install the flush fitting cap and the radiator cap.

Bubbles are Baaad, M'kay?

My LT1 Camaro had a bleeder built in. I imagine it was for this reason..

You still have air in the system. It may be trapped or it maybe from something like a cracked head, but you definitely have air.

Go to a good parts store get a blue tablet you drop in the rad if exhaust gases are mixed with the coolant it will turn the antifreeze blue. if no gases it will stay green. Sounds like you might have a hairline crack in an exhaust seat, that just weeping a bit of exhaust in to the system.

44

Also, as an aside, has the cooling system been flushed?

You can remove certain lines if you know that a product like the radiator is good but personally start fresh and be happy.

• Go to parts store

• Get a gallon of antifreeze

• Get two bottles of Prestone radiator flush

• Get a bottle of Blue Devil

• Get a water pump

• Get a thermostat gasket

• Get a replacement radiator

• Go to supermarket

• Get 10 gallons of distilled water

• Go to truck

• Remove heater hoses from heater core and using your garden hose flush forward and backward until no debris flows free

• Drain all old antifreeze from system, occasionally add distilled water and run through until water runs clear

• Remove thermostat

• Add one bottle of Prestone cleaner and top off with distilled water and run 10 minutes

• Drain all cleaner from system, occasionally add distilled water and run through until water runs clear

• Add one bottle of Prestone cleaner and top off with distilled water and follow directions on Prestone bottle

• Flush system until clear

• Install Blue Devil per directions

• Replace water pump

• Replace thermostat

• Replace radiator

• Add proper mix of coolant and distilled water

• Burp system accordingly

Drive forever

Are you sure the gauge is working properly ?

Although it does sound like a gummed up cooling system.

The heater temp goes up/down with the gauge, so I think it's reasonably functional.

I'm leaning toward a blockage, or small headgasket leak, as I noticed when I was warming it up w/the rad cap off coolant was getting pumped out the filler neck. That would also explain why the lower hose never got hot. The system was pressure tested OK, but that was before I got it.

I guess I'll start w/a flush & fill, and try the dye. Then go from there.

Thanks everyone!