2006 Suzuki Forenza with (GM/Daewoo) 2.0 I-4
~150,000 mi - always maintained well - have owned since new.
Timing Belt broke last year (Fall 2014)
I installed new Timing Belt Kit, Water Pump, Idlers, Oil Pump, FelPro Head Gasket, Alternator (noisy bearing), serpentine belt, front exhaust pipe & gaskets, new exhaust and intake manifold gaskets, new valve cover gasket, rebuilt head, using NEW casting, thermostat, DexCool coolant. Have been working on cars for 35 years - did the work myself. Followed all procedure, and everything went together well, and parts all seemed fine at the time.
Has been running great for about 9 months and does NOT overheat ever around town. However, when I take it out on the highway, it starts to overheat after about 5 miles at 60mph or above. If I slow down slightly, or pull over, temp drops right down and it runs at normal temp for another 4-5 miles and then starts to creep up again. I then need to slow down or pull over for a minute, and repeat the process. The car will run all day long at 50mph without budging from normal temp, however, soon as I get above 60 for 5 miles straight, the problems start.
Sometimes it heats up to the 3/4 mark and stays there for a few minutes. If I drive a little farther, it will go back to “normal temp” “1/2 mark” on it’s own, with the gauge behaving just like a “stuck thermostat” that just opened and allowed engine to cool. Sometimes it doesn’t and creeps up higher, close to the red line. . . . then I need to pull over or slow down to perhaps 40mph to allow it to cool. When I watch the gauge, I am convinced it’s a stuck thermostat by the way it behaves. . . . . but there was a brand new thermostat installed when I replaced the head. This highway behavior started right after I installed the timing belt, new head, and new thermostat, etc, but lived with it the last 9 months, since I really haven’t done any highway driving with this car.
Today, tried installing a new pressure cap on the overflow tank to see of that was the problem. Did not affect problem - still overheats after 5 miles on hwy.
Just pulled the thermostat today and did a coolant flush with a garden hose. Coolant looked good (and looked clean in tank), and I didn’t see any obvious sediment come out. Flushed from radiator hoses, backflushed through the thermostat opening, and flushed through the overflow tank. Ran car today with a bottle of Prestone Radiator Cleaner/Flush and plain water. Still overheating after 5 miles on highway.
After I dump the radiator cleaner on Sunday or Monday, I am going to install another new thermostat, and see if that solves the problem.
Hoses look OK (they are still original hoses), but don’t seem to collapse when you rev the engine when warm. Perhaps I should replace these. . . . but it’s not obvious they are the problem.
One of the first times the car overheated on the highway (got close to the red mark), I pulled over and popped the hood to see what was going on. Both upper & lower hoses were rock hard and I could hear the coolant boiling in the overflow tank. I cracked the cap to relieve the pressure, screwed it back on, and turned around and drove home. Soon as I started off again, temp was back to “normal”, but crept back up after 5 miles or so on highway.
I haven’t popped the hood on the side of the highway since that day, and don’t ever hear coolant boiling when I pull over. . . . but just thought that incident might help with diagnosis.
I have also sprayed the radiator fins from both sides to clean out any debris that might impede airflow. Externally, radiator looks to be in good shape - fins are good, not bent, and no corrosion. Don’t see any external coolant leaks in radiator, hoses, engine, etc.
Both radiator fans work and come on as intended - however, even if fans weren’t working, it shouldn’t cause an issue at highways speeds anyway. If they weren’t working, I would have issues at idle, etc, when air wasn’t being forced through radiator core.
Since everything is “new” except radiator and radiator hoses. . . . any thoughts on what might be causing this issue? Any thoughts on what to look at or test?
I have NOT done a compression test to date.
Car never overheated before the broken timing belt issue. Could I have a faulty (new) head? Bad “new” water pump? Pump seems to circulate fine - when engine is warm and you rev engine, can see good flow in overflow tank.
Don’t see any obvious oil in coolant, and don’t see any coolant in oil.
Any suggestions anyone can provide would be GREATLY appreciated. Have been driving this car for 9-10 months, but can’t take it on any long trips and just use it around town because of the overheating issue. Let me know if you need any additional information.