Small overheating problem

[asavage]

Alternate scenario: a leak elsewhere in the system allows air to enter when a vacuum tries to form during cooldown, that air isn't at the radiator yet. Engine warms up, thermostat opens, the air "appears" at the radiator.

Lots of variables.

[philip]

Alternate scenario: a leak elsewhere in the system allows air to enter when a vacuum tries to form during cooldown, that air isn't at the radiator yet. Engine warms up, thermostat opens, the air "appears" at the radiator.

Lots of variables.

And how come air only builds up when the engine runs instead of the engine cooling down?

Hmmmm.

[kassim503]

Outcome based public education not withstanding, physics holds that pressure always moves from higher to lower. So new air/gasses introduced to a pressurized cooling system must come from a higher pressure source. Now WHERE would that be?

NOOOOOO!
Head gasket dosent leak, I had the coolant sniffed for hydrocarbons.

I like al's theory, I didnt really think about something liek that happening. I have yet to check the freeze plugs but I think something along the lines of that is leaking or something is leaking in a area where it would boil off before I notice it. Anybody know if auto stores rent the coolant system pressurizer tools? I was going to buy one at napa but it costed something like 100+ dollars.

Car still overheats when u idle in traffic or at lights, but now its not when it just hits operating temp, its after its been at operating temp. I guess the radiator is either clogged partially or isnt big enough, or both. I want to run one of those fancy aluminum griffin radiators, ebay it or something, unless I have proof that the factory unit is good enough in the most extreme conditions. I see them on ebay for around 150, or I could buy the factory one for 175.

[philip]

Outcome based public education not withstanding, physics holds that pressure always moves from higher to lower. So new air/gasses introduced to a pressurized cooling system must come from a higher pressure source. Now WHERE would that be?

NOOOOOO!
Head gasket dosent leak, I had the coolant sniffed for hydrocarbons.

Sorry. Using an infrared exhaust gas sniffer is not nearly as accurate as the liquid blue dye gas test. I have used both. The liquid test uses a liquid that turns from blue to clear in the presence of any significant CO.

Here's something for you to do.

From cold, let the engine idle until you are sure the thermostat has opened for the first time.

Shut off the engine.

Run the palm of your hand all over the radiator core. You are looking for perceptable variances in surface temperature. If or when you notice some areas of the core are hot while other areas are noticably cooler if not still cold, you have just discovered your cooling problem.

[kassim503]

Yup I had it tested with some kind of blue liquid inside a tuned up turkey baster. They sniff the gasses coming off the coolant and dont suck the coolant up right?

Yeah I did the feeling around the radiator for heat test, and all of it was mighty hot all around. I know the radiator is probably not operating at full efficency but not completley clogged. Has anybody ever had overheating problems with these cars before? It could just be me, becuase my daily commute usually deals with standstill traffic and I like my air conditiong.

I think I want to try to get ahold of one of these coolant pressure testers and keep it pressurized for a few hours, then my leak would probably show up then.

[asavage]

As I mentioned upthread, Salvy got an OEM-style radiator for $103 (shipped).

As an outside possibility, since your coolant had been so neglected: I have seen the WP's impeller fins rotted away. Very difficult to diagnose. However, you said you'd replaced yours recently.

If you're going to throw parts at it, the radiator is cheap for this rig, as Salvy proved. Are you certain you have good idle airflow when it's overheating?

[kassim503]

Wow its only 103! I thought it was 150 or so, but I guess I had a brain fart or something. Mabye ill order one from them, but I want to make sure the radiator is the main source of the overheating- I dont want to cover up the symptoms with a new rad when whatever was helping the problem gets worse, and I have to deal with the overheating twice.

For now im going to pull the thermostat just to keep the temps at a minimum, weather isnt cooling down and the traffic is certainly not going to go away.

i suspect the thermostat as my source of problems, its one of those fancy new stant super-stat styles, and the hole for it is so little, I have no clue how coolant is supposed to flow thru it. I think this was covered by a thread somewhere else- and the conclusion was that the superstat style is sufficent, but Im not positive on it.
Later im going to ebay myself a coolant system pressurizer, and hook it up to the car and find my leak.

Well at only $103 that radiator is a raging bargain, and I may want to call them up in the near future.

Also btw, when I removed my old water pump, the impellers where in horrible shape, real horrible shape. Actually the reason why I replaced it was because of failed bearings.

[kassim503]

Mabye the fan clutch is having trouble engaging at low speed. I hear the fan whine when it is over 1500 rpm, and not below. Im not too sure what rpm the fan actually has to turn to make a whine, but just by looking at the fan at idle I do notice a little difference between the clutch rpm and the water pump rpm. Is it possible my fan clutch is not making good lockup until it hits the higher rpms? I think it might be because fan clutches operate by the centrifigual force of the clutch turning.
Mabye ill dig around the JY for a clutch off a z car or a maxima, mabye I can pull one cheap to test it.

Also I won a ebay auction for a coolant system pressure tester. I guess its worth it, and it should be here in 3-4 days, so ill just live with the problem until then.

[redmondjp]

Wow its only 103! I thought it was 150 or so, but I guess I had a brain fart or something. Mabye ill order one from them, but I want to make sure the radiator is the main source of the overheating- I dont want to cover up the symptoms with a new rad when whatever was helping the problem gets worse, and I have to deal with the overheating twice.

For now im going to pull the thermostat just to keep the temps at a minimum, weather isnt cooling down and the traffic is certainly not going to go away. [snip]

If it's your radiator (any 25-year-old car with over 150K miles on it has a mostly-clogged radiator--word), removing the thermostat won't help any, as it's wide open anyway if the coolant is too hot as yours is. And as already been noted, with certain thermostat designs, the engine will actually run hotter with the thermostat completely removed! I still think you need to replace your radiator. If you want to have a car as old as yours be a reliable daily driver, sometimes you have to bite the bullet and fork over some $ (it's cheap when compared to a new car, with a shiny-new radiator in it that's not filled up with crud ).

Besides checking for external coolant leaks, you can also use your coolant system pressure tester to check for a head gasket leak, but not how you think (and this applies to gas as well as to diesel engines): with the engine cold and not running, you use the gauge portion of the tester to monitor your cooling system pressure while you pressurize one cylinder at a time, with that cylinder at TDC (so both valves closed), introducing compressed air to the cylinder via a compression gauge adapter or a leak-down tester (assuming that you have access to compressed air). The crankshaft may rotate a bit from the compressed air, but as long as the exhaust valve stays closed on the cylinder under test you're OK. If you notice any increase in cooling system pressure during this test over a several minute time period, you have a leak between cooling system and that cylinder (head gasket, crack in block, crack in head, etc). This method will detect a slow leak very successfully.

If you have a gross leak between any cylinder and cooling system, you don't need the fancy setup listed above--with the engine cold, start the engine and start squeezing one of the cooling system hoses to check for pressure buildup--if you get pressure very quicky, say in a minute or less, you most likely have a head gasket leak (this is a great thing to check when you are buying a used car and can't take it somewhere to get checked out). I read this on a diesel truck forum before going to look at a 6.5 GM diesel and sure enough, it definitely had a head gasket leak (or worse, possibly a cracked block--can you say $5K for new engine )--I passed on that one!

And as far as where the air keeps coming from inside your cooling system, if you have a closed system with an overflow bottle, you have a pinhole air leak somewhere in your system. In a perfect world with this type of system, your cooling system is 100% filled with liquid coolant at all times. As the coolant expands when the engine warms up, a small amount of it passes the radiator cap seal (due to increasing pressure in the system) and goes into the overflow bottle. As the system cools down, the coolant contracts, and this causes a vacuum inside the system which then draws coolant from the overflow bottle back into the system, via the small metal disk (one-way check valve) inside the radiator cap. My 1969 Cadillac had this type of system which worked perfectly (only old car out of about 15 I have ever owned on which this actually worked the way it's supposed to).

All it takes for this system to get air inside is (of course) a tiny leak--it can be just an air leak which is so small that it won't even leak coolant--this leak won't let any coolant out when the system is pressurized, but it will let in air when the system cools down. So instead of sucking coolant from the overflow bottle back into the radiator, the system will suck in air through the pinhole leak instead, and this air will eventually make its way to the highest point in the system (top tank of the radiator). Does the coolant level in your overflow bottle get higher and higher over time, or is it going down? If it's going down, then you have a leak big enough for liquid to leak through somewhere in your system, but as has been noted, it may not be big enough to actually see drops from as the coolant could be evaporating on the hot engine. Or it could be burned up in the engine, if leaking into a cylinder.

You know, if you wait a couple more months, the weather's going to cool down and you won't have to worry about this for another 8 months

[kassim503]

100% positive the fan clutch works, Also I doubt the thermostat is the source of my overheating, someday I will get around to pulling the T-stat, but for now revving it when stopped is working pretty well. Mabye the overheating has been with the car all along, mabye the fan running at the idle rpm isnt moving enough air. Last summer my temp gauge was a little iffy b/c the gauge sender was on its way out.

[philip]

100% positive the fan clutch works, Also I doubt the thermostat is the source of my overheating, someday I will get around to pulling the T-stat, but for now revving it when stopped is working pretty well. Mabye the overheating has been with the car all along, mabye the fan running at the idle rpm isnt moving enough air. Last summer my temp gauge was a little iffy b/c the gauge sender was on its way out.

I'm waiting for your wife and/or kids to weigh in.

[asavage]

(any 25-year-old car with over 150K miles on it has a mostly-clogged radiator--word)

Not if distilled water is used for top-up, and the coolant is changed regularly: every two years for silicate-containing green coolants. However, almost nobody performs a coolant change until a hose breaks or a water pump fails.

You know, if you wait a couple more months, the weather's going to cool down and you won't have to worry about this for another 8 months

Naw, the weather's never going to cool down -- haven't you heard of global warming?

[kassim503]

Well, I my overflow bottle leaks down, but verry slowly. Probably at a rate of one week a tank. Im going to wait for my coolant pressurizer to come in the mail and then continue testing. For now im just going to wait it out and keep filling coolant in every morning (its not alot). Still want that radiator though, but im not too sure if I want a new factory one- or just go high perf and do a aluminum rad.

But for now im just living with it, and ill pull the T-stat. According to the newspaper the heat wave would linger for a few more days, that means rotting on the interstate for a few more days (my new fancy job lets me commute).

Also I found there is a "ceiling" to my overheating, it only goes up to the 3/4 mark and around there it levels off, what temperature that exactly is, I dont know. Sure hope its around 200F and not around 240F.

[asavage]

Well, I my overflow bottle leaks down, but verry slowly. Probably at a rate of one week a tank.

That's a lot. I consider losing more than a quart per 3k miles to be excessive.

[Carimbo]

I wonder if the same problem that causes the over-optimistic fuel gauge can also cause a higher-reading temp gauge. Kassim have you tested the water temp in a different fashion? Infrared thermometer pointed at t-stat outlet housing, for example. Would the housing need to be painted black, or black tape applied?

My diesel Maxima was losing water, at a slower rate than yours, but the rad was always full to the brim. When I recently cleaned the engine compartment I noticed some green liquid in the depression of the top rad tank-to-fin body seam. Turns out the overflow hose had a tiny leak where it connected to the small brass tube coming out of the fill neck. Apparently it allowed coolant to leak OUT, but not air to leak IN. Normally the leaked coolant was hidden from view by the plastic fan shroud covering the seam depression, then it would rapidly evaporate off the hot radiator.