v745ti

Hey all long time lurker, haven't posted in a few years but I wanted to pass on my gratitude and hopeful good news regarding my newly acquired '98 4Runner Limited 4x4 w/171k mi. I'm not sure if this post belongs in Off Topic or here, mods feel free to wield your banhammer / mod powers and move it wherever it belongs.

BLUF: replaced radiator cap and thermostat w/Toyota parts, jiggle valve at 6 o'clock, burped system, temp via scangauge II a solid 190-193 with A/C on under load.

Narrative:
The wife wanted an SUV (big surprise there) and I suggested a 3rd gen 4Runner. She said yes so I was off to the internets to score something in the $5000 - 10000 bracket.

Lady luck smiled on me and someone 4 houses down had a desert dune '98 Limited that she was at wits end with. In the past 4,000 miles and 12 months she had spent $6500 at some mechanic to diagnose her overheating problem.

New radiator, thermostat, water pump, fan clutch, A/C condenser, t-belt, all new hoses upper and lower, new soft lines to rear heater, coolant flushed, leakdown test, coolant analyzed for hydrocarbons... all with no fix. (Thanks to enapa I also checked for the "L" on the driver's side head gasket on the back corner of the engine... its there).

A mere $1500 later I was driving this beast back to my house with the heater (front and rear) on blast and staring intently at the temp needle and my Autel.

After that it was off to the internets once again (primarily yotatech and t4r) looking for possibles.

This past week I replaced the radiator cap, which despite the brand new radiator was the original Toyota unit and the cap portion had actually separated from the lower spring/rubber gasket part, and the thermostat which again despite being "brand new" actually looked like it had been there for a while (and the jiggle valve was clocked incorrectly).

I refilled coolant with the front end jacked, spilled coolant all over the carport after I unhooked the heater hose at the back of the engine bay (whoops). After not really cleaning up my mess and pissing off the neighbors, I started filling the radiator up instead, and once at the top I cranked the front and rear heat and started the vehicle.

At idle the temp needle slowly went up to just under 1/2 way while I burped the cooling system. At this time I never saw any constant bubbling, just a few occasional burps. I did this 3 or 4 times, started, let it get to operating temp, burped, shut down and let cool. Each time I'd add about 3/4 of a cup of water/coolant to the radiator and some to the overflow to let it suck it in when its cooling. I kept an eye on the exhaust and having blown many a head gasket in my time know what burning coolant looks and smells like... didn't see/smell anything out of the ordinary.

Fast forward to this morning, I was confident enough to take it for a 15 - 20 mile drive after a few 5-10mi neighborhood jaunts to get my dander up... and so far so good! We went up into the mountains, took Mulholland from Malibu to Beverly Glen, beat on it, went easy on it, all the while the A/C was blasting on cold. Really wanted to stress test this thing before I signed off on it. I took the scangauge from my other car and brought it along on this ride and saw nothing over 193f on the entire trip (wife driving, me staring intently at the coolant needle and scangauge).

So fingers crossed, I'd say we're in the green here! I'm still once-bitten-twice-shy on this thing, and noooo waaaay the wife will be driving it full time before I am 100% comfortable nothing is amiss but I think we're in the clear, all thanks in large part to Yotatech and the folks who have gone through this before and shared their experiences.

I'll keep this thread updated as the weather starts to get warmer, or if anything breaks but again wanted to express my gratitude for people sharing their expertise and experience.

Again, sorry if this is in the wrong forum,

-Ryan

v745ti

For reference, I pulled the thermostat that was in there and tested it. It started opening at a constant of 181f and was fully opened at a constant 195f (+/-0.3f).

The Toyota thermostat started opening at 176f and was fully open at 195f constant (+/-0.3f).

Test environment: one medium pot full of 3/4 gallon of tap water, one Thermoworks Chef-Alarm digital thermometer and probe mounted on the side of the pot with probe end submerged 1" and adjacent to thermostat body in the middle of the pot, on a gas kitchen stove, one Toyota thermostat and one Motorad branded thermostat labeled "82c" suspended with wire clothes hanger in the middle of the pot not touching any portion of the metal of the pot. Ambient temp 72.1f. Both thermostats had their gaskets on, its what I used to suspend the unit in the water from the hanger.

I found I was able to regulate the temperature of the water to within .3 degrees by switching the burner to "2" once a temperature 2f below the desired temperature was reached. The temperature would continue climbing slowly until it hovered around the desired temperature. This gave the thermostat time to heat soak and do its thing.

I understand this is hardly scientific (small sample size, environment overflowing with uncontrolled variables, etc) but its how I typically test thermostats. YMMV.

Bottom line is that in my case, the off-branded thermostat opened at roughly 5f hotter than the Toyota unit, however both were fully open at roughly the same temperature.

This probably isn't news to anyone, and probably doesn't make a lick of difference, but I thought I'd post it here anyways in case someone was curious, or if anyone out there is compiling data.

Jomoka

We've had a similar experience with my wife's '96 4Runner, and the radiator cap. Such a seemingly insignificant item, but that little center spring loaded valve is very important to keeping the system pressurized properly.

I've messed around with cars a fair amount in my life, and none of them (mostly older things) never really cared *that* much if the cooling system was pressurized or not. But on year, out on a road trip in Colorado, it started to burp coolant, at stoplights you'd see a bit of steam coming out from under the hood, the overflow bottle was spitting coolant, and when it would cool down it was low (and thus more prone to overheating unless it was refilled). I'd have sworn it was a headgasket the way it was acting. Then when I took off the original Toyota radiator cap, the center section had broken off and stayed put. Ah-hah! It was in a small town, late on a Saturday, the best we could do was an aftermarket cap from Autozone. I honestly didn't think it would help much (based on my past experiences), but it 100% cured the overheating, instantly. We went on into Utah and spent a week driving around in 105+ degree heat with the A/C blasting with no issues at all.

Then on the next year's trip (why does it do this on road trips?) it developed the exact same symptoms. Driven hard in hot weather, it would burp coolant out. I took off the cheap aftermarket radiator cap and found that it had failed - the center spring loaded thing was still attached, just no longer spring loaded. This time we were able to find a Toyota dealership still open and got an OEM replacement, which should hopefully last the same 16 years as the first one, instead of the 1 year the cheap-o replacement did. This second time, the new cap also completely cured the overheating/coolant burps.

v745ti

Wanted to do an update 1 week on. So far so good. No news to report, other than I got it up to 194 today for the first time in stop-n-go on the 405 with 85f ambient (IAT read 117f) and the A/C on full blast.

Checked the coolant level after the drive, rock solid where it needs to be. I think the problem is in fact fixed... by a radiator cap (oh and I bypassed the rear heater core - that was leaking, too).

vital22re

iTrader: (2)

Its been noticed that just installing the thermostat correctly (6 o'clock jiggle valve) can show a variance of 5-10 degrees. Sounds like you got it figured out.

v745ti

Another week, another 300 trouble free miles, most of which had the A/C on hauling people and gear between San Diego and Los Angeles.

Thanks again Yotatech!