So three years ago I was driving over Loveland Pass in Colorado, and right as I approached the summit, the engine temp flew up to the red and all my coolant poured onto the ground. I had to get it towed to a shop, and they informed me the cause was the radiator cap failing because the seal had gone bad. They replaced the cap, and all has been well for three years.

Until yesterday. I was on my way home from climbing a mountain and then suddenly, (after a pretty aggressive maneuver I will say), I saw my engine temperature go up close to the red. I gave the throttle a rest and turned on the heat, and fortunately I was going down a big hill so I left it in 4th gear and let engine braking do its thing and the temperature cooled back down to normal. I turned off the heat just because I was cooking, and everything was fine continuing down the hill. Then, I started ascending the next hill on the highway, and the engine temperature gauge started rising again. I turned the heat back on and it was only blowing cold air. The temp kept rising to red so I pulled off the road and shut it off, and subsequently steam came pouring out of the radiator cap. My car also gave me a low oil light and check engine light.

Opened up the hood, witnessed steam continuing to pour out the radiator cap, checked the oil and saw that it was low. There was still oil on the dipstick, but it was down below that bottom level marker. I guess this makes sense to me as my car has burned oil in the past and led to a low oil level. I haven't checked the oil level in a month so it probably burned down to that low level over time. I don't know if the level was low enough to cause increased heat in the engine... if there was still oil showing up on the dipstick and it was of good color, do you think it was low enough to cause additional heat stress?

Regardless, there was no coolant in the tank after it finally stopped steaming and I had to get my car towed AGAIN. There was also visible green coolant sprayed on the engine.

So what I'm assuming is that the radiator cap failed AGAIN. The heat not blowing hot air right at the end, in conjunction with the temperature gauge blowing up, I assume was due to a loss of coolant through the radiator cap seal. Then I guess the coolant boiled and steamed out as the engine got hotter when I pulled over. When I first noticed the engine temperature rising yesterday, my guess is that was the official break in the seal of the radiator cap, but there must have still been coolant in it, and then with going down the long hill with engine braking and having the heat on, maybe that kept the cooling system working even with the faulty cap. But then once I hit the gas again on the next hill, only minutes later, that faulty seal led to overheating once again, coolant blowing out of the cap, the heat not working and the steam. The check engine light I imagine is related to the cooling system, and I wonder if perhaps the oil light came on right before I turned off the car because the sensor was triggered by those other issues?

The only other thing that confuses me a bit is that it seemed like right before I turned the car off, while I was pulling over, that the engine was dying. The RPMs started dropping really low like down to 400rpm. This was in conjunction with the oil pressure light and the steam blowing out of the radiator cap. The temperature gauge at that time had just touched red, it never went higher than touching the red before I turned it off. Could it be that the engine was too hot and somehow that was causing it to die right there at the end? Like I said, I turned it off so I didn't really get to evaluate what was going on in that regard.

Is this all related to the radiator cap failing once again? I know I need to add oil, and it has no oil leaks but like I said, that's been going on for a while. Let me know what you think. If it's a different cooling system issue, or a different issue entirely, could that cause the radiator cap to leak? Or do you think the CAUSE is the radiator cap leak? Thank you all. My truck has been towed to a local shop and they told me they can't even look at it until next week so I'm trying to figure this out on my own.

BTW: 1999, manual transmission, 3.4, 240,000k.

As long as there was oil visible on the dipstick, it is unlikely that low oil damaged the engine. Obviously top up to the full mark and try to keep it between the high and low marks in the future...

As for the coolant - it can be a number of things. If a cheap aftermarket radiator cap was used, that could be the reason it failed. It could also be as bad as a blown head gasket... Or stuck thermostat, bad water pump, broken radiator, etc.

-Charlie

I suspect a bad head gasket as well. The coolant doesn't always go into the oil, sometimes the oil goes in the coolant. That would explain your mystery oil loss as 5VZ-FE's don't burn oil. The oil does absorb and retain some heat so a loss of oil could cause certain parts to get warmer than normal but not enough to boil off the coolant I don't think.

I believe that after the first overheat and you said it started blowing cold air, all of your coolant was gone at that point and not entering the heater core and a breakdown was inevitable. A new radiator and a head gasket test/leakdown test would be in order.

The "low oil light" is actually a low oil pressure light. There is a decent chance that it wouldn't build enough oil pressure in the 0-400 rpm range for the sensor to register it as enough pressure. As long as you didn't run it for an extended period of time like that AND it did not have that light on while you were at high revs, your bearings are probably fine. Go and put some oil in it and see if it will start up for 20-30 seconds if the shop you took it to will let you.

I would suggest having the shop test the compression of all of the cylinders before you throw any money at fixing it. As the others have said, there is a fair chance of you having a blown head gasket. The other problem with overheating these things is that the middle cylinder of either side head can crack the head between the exhaust valves with warpage.

If your compression checks out, do whatever your preferred method of head gasket testing is. A simple way to see if any coolant was getting into the oil is checking for milky residue sitting inside the cup of the oil cap. The head gasket test I'd suggest is this one that you can rent at the auto parts store and buy the fluid with it. How to Test a Blown Head Gasket in Your Car - YouTube

Update us with results and we will help point you in what direction to go in.

I would start by doing a compression test and testing the radiator for combustion gasses. Attention Required! | Cloudflare
I would also get an oem radiator cap, assuming you are running an aftermarket. Sankei is an oem supplier for Toyota and you can get them through Napa, might save a buck over the dealer?Attention Required! | Cloudflare

Good luck

(Edit) I don't know why my links are showing up like that, they where links to Napa?

I suggest you do a leak down test and forget all of the other methods. A leak down test is the gold standard for testing for a bad HG among other things. I have one of those dye test kits and it never once even remotely changed colors even though I had a blown head gasket (granted it was a minor leak).

Once I did a leak down test and pressurized cylinder #3, air bubbles came out of the radiator. This is how I 100% confirmed I did in fact have a blown head gasket. Either pay to have one done or if you have an air compressor, you can buy a leak down test kit for around $60.

I agree with Mike but I would first do a compression test of all the cylinders and would then follow that up with a leak down test of any cylinder with a low value to find out where you're losing the compression.

I did a compressoin check, a leak down and one of those chemical dye things for the radiator. All tested good, but I was still loosing pressure and a slight amount of fluid. Replaced cap OEM and the hose from radiator to expansion tank. All seemed good, but would still lose pressure....top hose would collapse. Thought....darn,...I have a bad head gasket. Ended up I had a block heater that was leaking a bit.
while yours had excessive pressure...and mine was oppoiste....just saying dont rule anything out.

one side note: When I was going to do my compression check ( and new plugs and wires) 2 of the boots that go from the coil to the plugs were stuck to plugs, they were a major pain in the arse to get out. Some coils have them perm connected, some dont....mine did not....and it was a major pain to get them out

A borescope for your cellphone is another good way to look in the cylinders for any antifreeze.


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