rp1947

First post here. Used this site many times over the years and see several users that appear to be very knowledgeable. Here's my problem.

Have 1994 4runner v6 auto with 323k and a potential head gasket problem, but shop tests say otherwise. This all begins last April when my 4runner approached a stop light and died. Next thing I notice is the temp gauge is past red with no prior warning. Got it started long enough to get it out of intersection, parked it safely, called 2 repair shops that I've had experience with to find an opening and then a tow service. With 320k, I was concerned about other damage before beginning repairs, but the water pump housing was destroyed and losing water faster than they could pour it in. At 280k, I had the timing belt renewed as scheduled and the original Toyota water pump was replaced with a Gates water pump and other parts. Totally came apart after 40k. Thus a leak down test couldn't be performed until after $1300 plus of parts and labor, all genuine Toyota this time, not risking Gates again. It passed the leak down test.

I've been adding coolant regularly since. Found a bypass hose that leaked and needed replaced and had it tested afterward by another shop using a coolant exhaust gas tester and they concluded no head gasket problem, but noted pin hole leaks in radiator. Purchased and installed new radiator and hoses. The place I park at work and in my garage have absolutely no signs of coolant on them, but coolant loss is increasing. I can only conclude a head or head gasket problem. Spark plug #6 is wet and I have a miss when idling.

How can it pass two different tests for head gasket failure? It appears that I have a unidirectional coolant breach in which coolant is going into the combustion chamber, but gases aren't making it into the coolant. My initial thought is that I have a cracked head instead of a head gasket problem, I certainly let it get hot enough. Before I spend the thousands this will cost, is there something I'm missing?

dropzone

iTrader: (6)

had to play with your font color to make it show up as your post appeared to be blank

1stgen88t4r

My 88 had a coolant leak from the bypass hose that comes out of the throttle body into the front of the motor. It never hit the ground. It evaporated on the hot motor. See this post

https://www.yotatech.com/forums/f116...0-3vze-289568/

rp1947

Don't know why it showed up in red, but used the edit function and changed font color to Automatic and seems to have fixed it.

Some minor leakage from the intake manifold gasket noted when water pump was replaced. Minor dried up red coolant around #1 cylinder, but nothing significant. My coolant loss is in the vicinity of a gallon of coolant every 100 miles or less. Have to monitor it constantly. Think I would see more under the circumstances, but no harm in taking a more thorough look with a flashlight. My main curiosity is if it's possible to have a unidirectional coolant breach and what does it indicate about the cause?

rp1947

Haven't had any replies in a while and haven't done anything but add coolant, change #6 spark plug a couple of times and try to think this problem through. As noted originally, the engine has passed leak down test and coolant gas test. Thus, first premise is there is no crack inside the combustion chamber. Without detailed information about water jacket route inside head, I can only conclude that it is more likely that the breach is before the cylinder head and in the intake manifold or intake manifold gasket, but haven't much knowledge of the coolant route in the intake manifold. As noted in the first post, the problem is unique to cylinder #6 requiring regular spark plug replacement on that cylinder. The spark plug gets very black and wet, all others remain gray and dry.

Have a little time today and plan on finding a shop to look at it. I'm over 70 and just not ready to attempt this myself. The local Toyota agency is about 20 miles away, but not convinced that they would have any more knowledge of this vintage of 4 Runner than a good general shop.

dbittle

You might get a compression test done and have them pressure test the cooling system. Number 6 is often the problem child for the head gasket, but I would expect its plug to be steam cleaned, not black and fouled. I don’t think you have the smoking gun yet.

akwheeler

I agree here, what I would suggest is to ask the shop to pressure test the cooling system, pressure it up and let the truck sit like that for a while and start looking for where the coolant is going.
check the carpet on the passenger side under the heater (possible heater core leak)
pull the spark plugs and see if one or more cylinders are filling with coolant (rotate the engine with a wrench and see if coolant comes out).
I have seen some funny things happen with coolant leaks that will only leak when hot (or cold) and I have seen times that a head gasket leak or cracked head would not show up on a cooling system exhaust gas test.

rp1947

Thanks for your replies. Checked around heater before and not found anything. Likewise, nothing under the 4 Runner when parked and nothing noticeable on top of the intake manifold, in the engine bay or anywhere on the undercarriage. Exhaust definitely smells sweet and convinced that it is burning away. Depending on the air temperature, I get very little steam, and only for a short period after startup in very cold weather. In warm weather, there is no steam, but noticeable sweet smell at all times. Pressure testing the radiator is a good idea, especially since the radiator and several hoses are new, but if it loses pressure over time with no noticeable outlet, what does that conclude? I suppose a pressure test with plugs removed and slow rotation might pinpoint the affected cylinder, but I already have that from the spark plugs.

Taking it back to the shop that replaced the water pump and doing another leak down test to see if they get the same result, but couldn't schedule it before the end of the week. One interesting reply when calling around about having it looked at. One shop that advertises as "Toyota specialists" said they would be glad to test it, but would not work on a Toyota engine this old if they found a head gasket or manifold gasket problem. The shop I'm going to said they would do the head gaskets if needed with no problem (course they didn't mention $$$).

2ToyGuy

I would guess that if it's burning off coolant, and has a pressure leak problem, it's a head gasket.

Just my guess.
Pat☺

akwheeler

If you are losing coolant it is going somewhere. either into a cylinder (likely since you now told us you smell burning coolant when it's running) or into the oil pan, or through the intake into a cylinder.
if you pressure up the cooling system with the appropriate pressure test tool and the pressure drops you will be able to find it somewhere!
it's just a matter of looking in the right place.

Jimkola

Have you used a block test yet? Those tests are easy to do, and pretty conclusive.
Your local chain parts store might have a loaner kit, you just have to buy the fluid. If not, kits are fairly inexpensive on Amazon

akwheeler

The block test kits will only tell you if combustion gases are getting into the cooling system.
if you have already determined that you are losing coolant do a pressure test and see where it's going.
Intake leaks don't show up on a block test, I have also seen head gaskets leak to the oil pan without showing up on a block test.

Jimkola

Passing a block test will at least remove the head gasket from the list, or at least move it to the back while you focus on other possibilities. You’d hate to address a bunch of minor seepages, only to discover a head gasket issue last. But each person has their own methodologies. I think block test and pressure test go hand in hand when addressing coolant loss. Well, after you look under your vehicle for dripping. That’s always first😀