Coolant Leak

Hey guys! I've got a coolant leak issue that I would love some insight on... For reference I have a 1998 4Runner SR5, 3.4L V6 with 430,000 miles. Original engine, transmission and head gaskets. Timing belt, water pump and T-stat were done in 2020 and I've never had any coolant leaks or issues before this.

A few weeks ago I took a little road trip (about 300 miles RT). Truck ran great, absolutely no issues on the drive up but the following morning I noticed a baseball-sized coolant leak coming from near the front passenger side wheel well. On my way to go pick up some more coolant (I had been driving for maybe 7-10 minutes) my heater core valve totally busted, spraying hot coolant everywhere. I pushed my truck off to the side of the street, walked to the nearest gas station and got enough coolant to refill my empty radiator. There was an O'Reilly's 5 minutes away so I limped it over there, having to pull over twice to avoid overheating. They had one heater core valve in stock and I replaced it in the parking lot. (I should mention that the failed HCV was the original and it was totally rotted out. The hoses that connect to it were in good shape.) Drove back home with the A/C on (it was hot outside, about 95F), no overheating, truck ran fine. After getting back I noticed that I still had a coolant leak, however it's now coming from near the thermostat housing/oil filter/oil pressure sensor area. I replaced the thermostat a few days ago, but no change and I monitor it constantly while driving to make sure that it doesn't overheat (which it has started to 3 or 4 times but I pull over before it gets above 220F). Oil's clean, no coolant. I'm praying it's the water pump, which still sucks but it's better than head gaskets. I'd really appreciate any input!

Thanks again!

 

Doubtful a head gasket. Probably the oil cooler for the engine. Sounds like it's time to replace ALL your coolant hoses throughout.

 

That's good to hear! Thank you, I will definitely start in on replacing the hoses. I'm almost positive they are all stock. I ordered a new Aisin water pump today just in case, so if I end up not needing it I can always return it or keep it as a back up. Unfortunately the WP that's in there now is an Import Direct from O'Reilly's which I know isn't ideal, but I had limited options at the time and that was the quickest and easiest way to get my truck back on the road.

 

A bad head gasket will generally not simply leak outside the engine. Usually it will cause overheating. The leak tends to be to the cylinder because of the high forces in that area.

 

Well it turns out the coolant leak was indeed the water pump. However I'm still overheating. It runs at normal operating temp until I start driving up the mountain to my house (about 3 miles uphill at 40-50mph) by the time that I get to the top to turn down my road the temp is at 220-230 degrees. Too hot. What's odd to me is that it didn't start overheating until the heater core valve blew. New heater core valve, new OEM water pump, new thermostat... Maybe something simple like my radiator cap? I'm thinking I should maybe start with a coolant flush... Any ideas or suggestions? Again, never had any overheating issues before this. Thanks in advance!

 

I should add that my radiator is not stock but I've never had any issues with it. Radiator fan and fan clutch seem to be working fine. I do remember when my water pump went out in 2020 I had to replace the radiator cap. I don't know if that's relevant or not.

 

Pressure test the system don't guess.

 

Thanks, I will do that next.

 

That and test for exhaust gasses in the coolant. If you've overheated the engine, even just a little, you may be looking at a bad head gasket.

 

That's it. Pressure test it and be ready to do all the hoses - cracks are sometimes difficult to spot. Good luck.

 

Just wanted to give you guys an update and say thanks for all the advice! Turns out it was the radiator. Installed a new one and it doesn't get over 192 degrees coming up the mountain now. What a relief! Really interesting chain of events though. Heater core valve literally blows apart, then the water pump starts leaking and finally the radiator. It was a learning experience. I definitely know a lot more about my cooling system now! Haha.

Thanks again gentlemen!

 

mogie... Thank you for the follow-up on the resolution of your overheating problem. Many people ask for advice, get useful replies, and then never come back to say what the problem was or even say "Thank You".

I had something similar with an Alfa Romeo Spider that always ran hot. I tried a new thermostat, electric fans, hoses, and flushing the original radiator. I finally replaced the radiator and now it never overheats.

 

You're very welcome!

 

cool deal mogie... i was fearing the worst - head gasket.... one incident on old aluminum heads is sometimes all it takes. PS, I have a reman VZ ready for the 4rnr I am restoring - the current VZ becomes a 'nipoon steamer' when it warms up, spewing prodigious amounts of steam thru the exhaust. Head gasket or cracked head. 287,000 miles is all.

KEEP ON TRUCKIN ! as was said many moons ago......

 

I was cautiously optimistic throughout the whole process but the possibility of it being a head gasket was always in the back of my mind. One evening when I was burping the coolant system a family friend stopped by on his way to my cousin's house and he took one look at it and immediately said "no way it's a head gasket." He's a bit of a redneck, drives semi-trucks for a living and knows enough about engines for me to respect his opinion, but one thing I've learned in the short 6 years that I've spent wrenching on my 4Runner is to not assume anyone's right just because they know about cars! In the end I always do some online research and then ultimately go with my intuition. Glad he was right though! I swear this truck is never gonna die. I love it. People think I'm crazy for keeping it alive but it's basically part of my identity at this point. Good luck and have fun with your restoration!