ddwyer

yayfortrees,

I checked the cap off the truck. The pressure test adapter has an annular ring that seals against the smaller, inner, spring-loaded region of the cap. The adapter then locks against the locking lip of the cap. In the side of the adapter there is a small hole that allows the released air pressure to escape. When I tested the cap, air escaped from this hole as soon as any pressure was applied. It seems to me that this indicates that the pressure holding portion of the cap is not working, or the seal with that portion is poor.

ddwyer

Yayfortrees,

Let's say the cap is bad. Wouldn't that have dumped coolant into my overfill reservoir when it overheated? My reservoir is virtually empty.

yayfortrees

Yes, it appears that your radiator cap is not holding pressure. A cap that doesn't hold pressure = a cooling system that doesn't hold pressure. If a cooling system can't hold pressure, the coolant will boil. When your coolant boils, you have all kinds of problems such as overheating, etc. It will also allow a lot of coolant to blow past the radiator cap, which then goes to your overflow coolant reservoir.

Definately replace the cap, and then see how it drives. About the compression test: I wouldn't worry too much about it at this point. It is really easy to get a faulty reading with a rubber-tipped compression gauge. I only use the type that threads into the spark plug hole.

I can tell you really want a problem with your head / HG to exist, but try fixing the easy and affordable things first. After replacing the cap, and IF it still overheats and/or loses coolant, then you can pull the head. But if a $5 or less cap fixes the problem, why bother with it?

Let us know what you find out. I'm really anxious to see if this takes care of the problem. I'm wishing for the best for you.

ddwyer

I will buy a cap tomorrow and drive the truck tomorrow night.

Maybe the "fix" won't work and I'll get to do the head/HG!

yayfortrees

Usually, yes, it would have forced coolant into the reservoir. But, wierd things can happen.

Try not to look at other data. As a former mechanic, the most revealing data at this time is the cap only holding 2-3 PSI. What else did or didn't happen is a result of a ton of variables. Variables that may or may not mean anything. But, what does mean a LOT to me, is the cap test result.

yayfortrees

Ahhh, you can't get a cap tonight? I don't know if I can stand the suspense!

ddwyer

I bought a new radiator cap, aftermarket 13 psi, local dealer had no caps in stock. Tested the cap as I did the original, it failed even worse. Clearly, the test fitting that "fits" my cap does not fit so well.

I put the new cap on and took it for a drive. It started to overheat (3/4 gauge) after I warmed it up and brought it up a hill at 35-40 miles per hour. I stayed off the freeway since I didn't need to experience full overheating again.

I pulled it back into the garage and shut it off. The overflow tank had a pint more than when I started and was clearly full of steam/exhaust? above the fluid.

Next steps?

leakdown on cyl #2? If so, how do I do the test?

ddwyer

I appear to have violated two axioms that I try to live by:

"KISS (Keep It Simple, Stupid)"
"It's not what you don't know that gets you, it's what you do know"

I *knew* it wasn't the t-stat and kept envisioning the complicated problems.

It appears to have been the thermostat. I bought a new one, took the old one out of the truck and plunked them both in boiling water. The new one popped open and the old one ...... nothing. I put the new one in the truck, drove it for 20 minutes, including an interstate run, and the gauge never got above 1/2.

As an added piece of data, I ran a block test (test tube with fluid, inserted into radiator filler, that changes color if exhaust gas runs through it) that showed no exhaust gas leakage into the cooling system.

Tomorrow I will run another compression test using threaded extenders that will allow me to use the thread-in compression gauge instead of the rubber-tipped gauge.

Hopefully, the data continues to support the t-stat problem and fix.

Kiroshu

Always start small and work you way up. Pressurize system which you did. If it held it for a half hour it was waay good and sealed even ten mins if it held it exact it was good. A faulty thermo stat can really throw off everything if not diagnosed correctly. IF the truck was over heating steam devlops from the water boiling that you put in it its going to get out somewhere, It was prob slowly steaming out a hose somewhere or the coolant tank hose..... and being to hot for a luquid state to hit the ground. If you suspect HG trouble check oil first. Second thing i would have done is if i could get a shop somewhere to pressuize each cyl with air and look for bubbles out the rad cap. If so then theres a sure sign of hg, cracked head, cracked block. Oh and a few things, water dripping out the tail pipe is indeed a biproduct of combustion. Theoretically speaking water out the tail pipe for emissions is considered perfect combustion.... theoretically... the water vapor(steam) would travel down the hot pipe till it met cool air at the end and turn back to water thus water out te tail pipe. Water does not leave the cyl in liquid form, it can't. It leaves in vapor. Oh and generally oil does not mix into the coolant system... infact hardly ever its vis versa.

4runnermt

Just reading this thread my first suspect was the thermostat! I'm glad you figured it out. Once I bought the fancy stainless thermostat for my truck, and it crapped out in a couple of days. Also I have had a bad radiator cap that allowed the coolant to steam out of the radiator.

swampfox

you can take a used spark that fits your truck ,break everything off and keep the part that screws into the head. weld a air fitting to it that will connect to a air hose. when you pump compressed air into the cylinder it will indicate different problems. if air come out the intake it could be a intake valve.out the tail pipe, exhaust valve. bubbles in the radiator ,head gasket. a piece of paper will help detect the air escaping. I saw this on a auto repair show. this is just suggestion to hunt down any future problems that the readers might have.

ddwyer

swampfox,

Thanks. Great tip.

ddwyer

update:

I fashioned an adapter for the thread-on compression gauge from two spark plug anti-foul extenders. I obtained the following readings with a hot engine with WOT (dry/wet):

1: 140/140
2: 140/150
3: 140/140
4: 135/xxx

Clearly, they are all very consistent. I am not concerned about the wet/dry differences since I had a hard time getting oil in the cylinders. I am also not concerned that they are on the low end since I have four leak paths in the compression gauge, one of which is a hand-tight connection.

I ran the block test again; it came up negative for exhaust gas.

I did notice the classic light brown froth in the underside of the oil filler cap. Is this from normal water vapor that rises to the top of the engine, or is this a sign of coolant in the crankcase/valvetrain? When I ccked the oil and pulled the valve cover, there was no evidence of the frothy stuff.

I am guessing that the t-stat caused the overheating. I am not sure where all the coolant went, but I watch the temp gauge and coolant level closely over the next several days.

yayfortrees

When supplying compressed air to a cylinder, you have to hold that cylinder at true top dead center compression (TTDCC). Best way to do that is to get a long breaker bar and socket, and use the nut on the crank pulley to spin the motor. You should only spin the motor in the normal direction, never backwards. This is essentially a leak-down test, except not using a gauge to determine the exact percentage of leakage. IIRC, a good leakdown is less than 10%.

BE VERY CAREFUL WHEN ATTEMPTING THIS!!! If you can manage to find TTDCC on a given cylinder, and then apply 100+ PSI, the piston is going to want to travel down. All it takes is less than 1 degree either side of TTDCC, and the crank will spin. It will normally only travel half a revolution, but it will do it quickly and violently. If your breaker bar is still on the crank pulley nut, it will spin with the crank. This can smash fingers, hands, and other accessories under the hood. If possible, use a valve between the air hose and the attachment screwed into the spark plug hole. This will allow you to slowly bring up the pressure. If the piston doesn't move, open it the rest of the way, giving full air pressure. To be absolutely safe, disconnect the negative terminal of battery.

If the piston is not at TTDCC when air pressure is applied, it will simply travel to near bottom dead center (BDC). Near BDC, your cam is going to start opening valves, releasing the pressure, and not giving any valuable information for diagnosis. If the piston is at TDC on the exhaust stroke, the air will simply escape through both the intake and exhaust valves.

REMEMBER: BE VERY CAUTIOUS WHEN PERFORMING THIS TEST!

ddwyer

yayfortrees,

Excellent info and warning.

Hopefully, I will not burn/consume coolant and I will not need to run this test.

yayfortrees

I hope everything is good to go for you! Keep us posted.

ddwyer

Update:

I re-filled the cooling system with 50/50 mix, burped it on an incline with heater valve open to get air out. I put in new oil and filter.

I drove around doing errands for about an hour. It never overheated; the gauge stayed at the half-way point. I saw no whitish exhaust. I smelled coolant a few times, usually when stopped at a light, but when stopped, saw no evidence of leaks. After returning home and letting it cool for two hours, the coolant was down below the fins. I added about two pints to get it full.

If you read previous posts, I noticed the following over the last several days:

+/- no evidence of coolant in oil (at least no white-ish froth. Oil was dark, but I figured it was dirty since I was due for an oil change).
+ no visible leaks onto the ground.
+ no evidence of exhaust gas in radiator (sniff test with chemical block tester)
+ similar compression in all four cylinders (140 to 150)
+ no sign of whitish exhaust
- whitish frothy stuff on inside, underside of filler cap

I am really puzzled as to where the coolant is going. Maybe I missed a big air bubble after refilling, but I think the smell of coolant is just too coincidental.

Is there a chance that I have coolant leaking into the intake manifold?

Any other suggestions?

yayfortrees

I guess there's always a chance of that, but I think it would be very noticeable in the driveability, and I'm sure it would show up on the spark plugs.

This last time you filled it, did you fill the reservoir up to the top mark? Have your drove it more since topping it off? If so, is it still losing coolant?

If you haven't already done so, I would top it off one last time, make sure the reservoir is filled up to the cool mark (assuming the motor is cold), drive it some more, then re-check the level.

For the first drive after filling the coolant, all it would take is one splash of coolant that didn't make it into the radiator/reservoir, and splashed onto something on the truck. When things start heating up under the hood, you would smell some coolant, mainly when stopped. Now if you continue to smell it, and it doesn't go away, then you've got a leak somewhere.

swampfox

you might check to see if the carpet, or under the floor mat it wet.the heater core might be leaking .

yayfortrees

Great suggestion swampfox. I hadn't thought of that.