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2001 Subaru outback, 280,000 miles. I believe the water pump and timiming belt have been replaced at least once along the way, but do not know for sure. We've only owned it for the last 35K, about 2 years. It's not an everyday driver, but we do get a lot of use out of it, and I keep up with basic preventive maintenance. I flushed the cooling system and replaced the thermostat and upper and lower hoses about 20,000 miles and 18 months ago. Not sure how old the radiator cap is. Can't recall if I replaced it at that time.
Yesterday, I drove about an hour and a half on a freeway, and then pulled off and entered a local street network. The temperature was around 80 degrees. As I slowed down for a red light, the temperature gauge immediatey began to climb rapidly toward the red zone - within seconds, it was already approaching the red line. I immediately turned the heater on full blast, and as I stopped at the light, shut the engine off and left the heater running.
The light turned green, and I restarted the car. The needle was a little lower just from sitting for a minute, and I went through the light and pulled into a parking lot. As I puled away from the light, the needle dropped, but as I slowed into the lot, it quickly began to climb again.
As soon I stopped in the lot, I popped the hood and checked to see if the radiator fan was running. It was. I shut the car off, ran the heater for another minute or two until it stopped blowing hot air, then shut if off and let it sit for 20 minutes. Meanwhile, I checked the hoses and looked for leaks. There were none, nor could I smell antifreeze. The engine did smell hot, though.
I restarted the car and quickly learned that as long as the RPMs are over 2000 or so, the temperature was completely normal. As soon as it dropped down to around 1000, the needle began climbing again. Using this trick to manage the temperature, I quickly completed 2 more errands, then parked it for an hour and had some Thai food. The temperature of the Thai food was on the high side, but not quite in the red zone.
After the break, the car ran much better, and I was able to finish all of my errands. However, it continued to be a problem - although on a much lesser scale.
Finished my errands, picked up a gallon of anti-freeze and a gallon of distilled water, and drove back home. 100 miles on the freeway/highway, about an hour and a half. Temperature solidly in the normal range the whole way. Needle never quivered.
Now - the first sign of this happened last week, on another road trip. After an hour at highway speed we pulled into a small town, and as we approached a red light the needle began to climb quickly. The light turned green before we hit it, and as I sped up the needle dropped again. It happened so quickly I barely had time to react, and it did not repeat. Since then I've driven about 50 miles around town, and watched the gauge like a hawk the entire time. Needle has never twitched, even on 90 degree days at full operating temperature.
So it only happens after extended operation at high RPMs, and as soon as I rev the engine back up over 2000, it stops. If I continue to drive for some period of time at low speeds, it is a constant problem until I let the engone cool down. If I am starting off with a cold engine, I can run at low speeds on local streets indefinitely without a problem.
I'm thinking most likely water pump, but if I'm going to do then "diagnosis by replacing parts one at a time" thing, I'd rather not use the water pump as my starting point. It doesn't "feel" like the thermostat, but I'm not ruling it out. As I said, when I checked the radiator fan it was running but I cant be sure it was running at the times the needle spiked. I'm kind of wondering if it might be an intermittent fan problem. Would the neede spike that fast if it were?
Coolant level seems OK. No sweet, smoky exhaust, so I'm hoping it's not a head gasket. The hose was too hot for me to properly squeeze while it was happening, but the little squeeze i gave it seemed normal. Not sure what else to check here. Any ideas?
Bad radiator cap or air bubble. Most likely the bad radiator cap overflowed coolant while driving and it sucked the tenant verflow back in the cooling system and created a air bubble.
I would get a new radiator pressure cap. They do go bad
with the ae and mileage on the car, i am thinking radiator. often times the first sign is in fact heating up at low speeds where the coolant flow is rather low. get the engine rpms up though where coolant flow is higher and temps come down. i think part of the core is clogged.
1. wash radiator. Or, blow it with compressed air. Do NOT pressure wash fins. HD engine cleaner and lots of strong water stream
2. radiator is under performing. Partially clogged or something
3. do hoses collapse after car cooled down? If not, do they feel spongy? Like hollow inside? Do you hear girgling noise when squeezing hose? Air bubble
4. HOW IS THE BELT? Loose belt will cause under-performing pump.
5. Pump is very simple mechanical device. it either works or not and if not - it starts with leak of screeching noise. Unless it's partially or completely has fins covered in build up - I don't think it's pump.
6. t-stat. The obvious.
unfortunately, this scenario is but one of the classic symptom sets of blown head gaskets in this engine.
You can verify the presence of combustion products in the cooling system by using a "blok check" tester on the radiator, which uses a chemical solution to change color in the presence of combustion gases. Or, as I do, use an old 2-gas exhaust gas analyzer to sniff the radiator bubbles. But for the most part, the reported symptoms are enough to tell me that the head gaskets are done ... and if the heads have been overheated at all, the heads are susceptible to warping beyond Subie spec AND the block is susceptible to cracks in the cylinders near the head gasket joint. I've seen this scenario a couple hundred times and friends in the biz who specialize in Subies have told me the same scenario many times.
neither the radiator or water pump will be the fault here. FWIW, the WP is driven by the timing belt, not an accessory belt. (Ukrkoz ... are you listening?) WP failures in this series of engine are virtually unknown. I've replaced many as part of the 100K timing belt/idler/WP/tensioner service and have never seen one that wasn't working perfectly ... even those that have been neglected for a timing belt interval. OE Subie t-stats are virtually bulletproof ... I've never seen one fail, even with 300,000 miles on it. If the radiator was underperforming, the car would be overheating almost immediately upon driving at normal speeds.
It might seem simplistic but you might want to replace the fan switch. Most engines have them located on the rear of the block, maybe near the oil filter. It's a low cost item that screws into the block to read water temp and is simply an on/off switch. It may have an intermittent 'going bad' problem. You wouldn't know the switch is bad while driving because the air passing through the radiator keeps the water temp below 'fan on' temp.
You could do a lot of speculating, or you could just start with a new $10 thermostat and a $7 radiator cap.
That might just fix it!
My guess is a stuck thermostat.
+1 or as the next poster notes an air bubble. Fill the radiator with the front of the car jacked up. Crud could accumulate in some cooling channels. I had this issue on two cars.
getting a laugh out of the "general" automotive knowledge posts on this thread.
this is a very specific situation that the layout of the Subie engine/cooling system ... and head gasket failures ... present.
OP, you've already replaced the t-stat and related items, and already filled the cooling system. There's no "loose belt" slipping on the water pump like can present on many OTHER CARS. If the cooling system on your Subie shows full at the radiator when cold, then the flow will have "burped" the air out of any pockets when you were driving. You've already verified that the fan temp sensor and fan system is working.
Seriously, if you don't have the means to properly diagnose this problem, you need to get this car to a shop that has SUBARU experience with the head gasket failures. Just for grins, you can do an online search about the head gasket problem in these cars. The early 2000's series cars, despite having the newer SOHC head (after the prior DOHC series engine) ... still had problems with these. A Seattle area Subie indie shop with a guy by the name of Stoob has many pages of posts about the head gasket failure symptoms and the repairs that his shop does to assure proper results ... worth looking at his posts.
On a personal note, every one of my 2000 and 2001 Subie's has had the head gasket failure problems, as well as all of my neighbors with these cars from 2000 through 2005. The dealership that I buy most of my Subies from in Fort Collins ... who specializes in Subie resales ... ALWAYS puts new head gaskets in EVERY ONE of the cars of this series before putting it out on the lot. Their techs have gotten it down to a half-day of work to R&R the heads, clean them up, check for straightness, check the block for cracks by the cylinders, and install new head gaskets. It's that common a problem on these cars, especially on the higher mileage engines. These cars routinely eat head gaskets. I consider it a maintenance item to be replaced at the first signs of distress ... some cars will get 200,000 miles on the gaskets, some only 50-75,000. For a DIY'er, it's not a big expensive deal to take care of if the engine has not been overheated. But put off replacing these in a timely manner and the heads get expensive when warped more than a couple thou.
Worth getting the "full kit" when doing the head gasket replacement, which includes all the gaskets/seals and NEW head bolts ... there's only 6 per side torque-to-yield and a very specific head bolt rotation pattern after an initial very low torque lbs/ft setting. IMO, very important to use a "degree rotation" reading torque wrench ... I bought a "Gear Wrench" brand 1/2" drive electronic torque wrench specifically for the Subie engine work I do and it's been a lifesaver on achieving specific degrees of rotation on the head bolts of these cars when doing the head bolts on the engine in the car on those models that have the room to do so.
PS: you don't need to "fill the radiator with the front of the car jacked up". The top of the radiator is well above the top of the engine. If you'll give a Subie a few moments to allow the coolant to flow by gravity up through the t-stat weep hole, it will eliminate most all of the air. You can promote this by "burping" the lower radiator hose. Running the engine for a few moments to circulate the coolant will bring the air to the top of the radiator, especially if you drive the car with what appeared to be a full radiator and then let it cool down for 20-30 minutes after driving to check the coolant level.
PPS: essential on this car that you replace the t-stat only with the OE thermostat. It's quite different than the standard aftermarket t-stats which don't give comparable performance. The wax pellet area of the OE t-stat is significantly larger than all other brands. It's a bit more expensive than those "cheapie" t-stats, but you'll not have any problems with the OE t-stat. In over 30 years of working on Subies, I have yet to see a failed OE t-stat. Suppliers such as Rock Auto will only sell the OE t-stat and not a stant or other cheapie brands that don't work as well in these cars.
Last edited by sunsprit; 08-07-2017 at 04:22 AM..
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