Hello all, I am trying to figure out my next plan of action and thought I would ask the pros here because I am stumped.
First off, my truck runs great and is my daily driver. It has 125,000 miles on it and has been maintained fairly well, nothing sounds bad coming from the motor. So, I was driving and noticed that the heater was blowing cold air even when it was heated up. I kept the heater on and the temp gage slowly went up to the high section and soon after showing a check gage light it went back down to normal temps and the heater started working again. I figured it was the thermostat and I know the coolant hadn't been changed in a while so after doing the same scenario a couple more times I finally had a chance to get a new thermostat and fluids. I figured I would change the oil as well (which was clean and had no water or coolant in it). So I drained all the coolant and blew it out and changed the thermostat. Easy job. I test drove it and the thermostat seemed to open and function properly. After about a 3 days it started doing the same thing again only worse. I thought it might be the thermostat again but didn't know for sure. The weird thing is it doesn't overheat and drop down to normal temps when the heater is completely off...? And one day I thought I would try the heater again and after starting it up one morning and driving it 3 miles the temp gage shot up again but this time I heard a popping noise and smelt the coolant from the heater. This hadn't happened before. I pulled over and popped the hood to find coolant had been sprayed everywhere. The coolant overflow bottle cap had popped off and the fluid level in the reservoir was near the top of the tank. I drove it another mile to get it home and no problems with it on the way. No overheating issues or anything.
So, my question is, Is the coolant not circulating right? Is it the thermostat? What are the odds of the new thermostat reacting with the same problems as the old one? I was thinking an air bubble too but why would I have the initial problem before I changed the thermostat or fluids? I made sure when I put new coolant in I squeezed the hoses while it was running and made sure to get as much air out as I could. Could it be the water-pump is shot? I am just getting an idea of what to check given my situation so I am not out of a truck for getting to work and school.
Any help would be appreciated.
Thanks!
Josh

 

The water pump could be bad but that shouldn't cause that much extra pressure the system has to be clogged somewhere or a slight head gasket leak fishing exhaust gas back into the system I'm pretty sure that is the only things that would cause pressure buildup like that but seeing as the heater is not functioning take a look at the heater control valve and unhook the hoses at the heater core and use a hose to force water through it and see what comes out.

 

Unfortunately you have a cylinder/cooling system leak, also known as a blown head gasket or cracked head.

These can start small, air from cylinder is pushed into the cooling system which forms an air block in the high side of engine which will block heater flow and raise temp, changes in RPM will often clear the block and the air is purged thru rad cap, heater comes back and temp comes back down.

Leak gets worse over time until cylinder pressure(600+psi) will start pushing coolant out the rad cap at startup, with the extra air in the cooling system coolant steams and pressure builds even more filling overflow tank and bubbling out.

Simple test is to fill cooling system cold, use water not coolant because it will be lost if it is a cylinder pressure leak.
Leave rad cap off
Start engine
If coolant comes bubbling out then............thats what you have.
A cooling system has no internal pressure when cold, pressure comes from coolant being heated above 180degF so it would take about 5 -10minutes of engine running for that.
Only other source of pressure are the cylinders, 150psi cranking, 600+psi firing.
Water pumps circulate coolant, no pressure is involved.

If you want to find the leaking cylinder or just confirm it is a leaking cylinder then do the Glove test.

The Glove test
Cold engine
Remove coil wire or connector, we want a "no start"
Remove rad cap, coolant should be at least an inch below top of rad, lower is fine but drain some out if it is at the top.
Remove overflow hose and block its opening in rad, vacuum cap from engine can work.

Place latex glove over rad cap opening seal it with rubber band.
Balloon or condom will work as well, yes condom, seen it work, lol.

Crank engine
Glove will pulse up and down if there is a pressure leak from a cylinder.

If you want to find which cylinder is leaking remove 1 spark plug at a time and crank engine, when glove stops "dancing" the last plug pulled was the leaking cylinder, reinstall it to confirm.

 

Thanks for the replies. I hope it's not a head gasket or cracked head that would be very bad....From what you are saying RonD I need to get it tested. I'm thinking about just taking it in somewhere that has a leak down test or compression test readily available. I really hope it's not the head that's the last thing I want to repair....
Why wouldn't there be coolant in the oil? Is it only leaking out the exhaust or something?...

 

If you ever look at a head gasket you will see the cylinder rings are surrounded by holes, these are coolant holes, where coolant circulates from block to head and head to block.
This is where all the heat in an engine comes from, the cylinders, so they are surrounded by a coolant jacket.

Most heads only have 2 or 3 holes that allow oil, that is pump up through the push rods to the valve train, to drain back to the pan, these are far away from the cylinders.
Over head cam heads, and some OHV, will have oil passages, but there just are not that many compared to coolant holes/passages.

So when a head gasket goes, it is always to a coolant jacket first, that's how you know there is a problem, over heating as "air" is pumped into cooling passages.

On older engines heads would warp and open a passage from cylinder to cooling system then if left long enough to an oil drain.
So it was maybe 7 out of 10 head gasket issues had coolant in the oil.

Newer designs and gaskets usually only show coolant in the oil maybe 4 out of 10 times.
So not unusual for oil to be clean, the ol' "water in the oil" thing is from another time, it still happens just not as much.

Just did a 4.0l with blown head gasket, didn't even change the oil.

Do the Glove test(free), or a Block test if you want to spend the money.
Leak down or compression test will just leave you in the same place you are now, wondering, neither is definitive for head gasket or cracked head issue.

Google: block test
It is a way to test for hydro-carbons in coolant, i.e. exhaust in the coolant
DIY kit is about $50

 

RonD,
Thanks for your help I can tell you know what you are talking about so I trust what you are saying. And looking at it now I think you are exactly right so I will do the glove test and if that shows probability then should I do the block test to make sure? I guess better safe than sorry that way....
How long does it take to break down the motor and pull the heads off usually? Should I do both while I have the chance or is it worth it?
Thanks again you've been a big help.

 

Glove test is definitive if positive, if glove bounces you have a leak from cylinder to cooling system, 0 doubt

If glove doesn't bounce then do a block test to be sure, glove test assumes closed cooling system with no leaks to relieve pressure.

If glove does bounce then start removing spark plugs to find which cylinder is leaking, it could be two cylinder so watch the glove.

Once you ID the cylinder it will make it easier for you to see where the leak is once head is off, if head gasket looks OK then inspect that cylinders head area, usually crack is between valve seats.

If you work straight thru 6-8 hours is easily doable.

I often drop by a local muffler shop, if engine still runs, and have them remove exhaust manifold bolts and header nuts, then reinstall snug but not tight.
Usually under $40 + cost on new bolts or nuts that were stripped or broken.
You might spend 2 hours and $50 on special tools to get out ONE stuck or stripped bolt/nut, these guys do this for a living so have the tools and know how, fast and painless for them

 

OK awesome. I'm pretty sure it's a leaking head gasket because now it overheats and acts weird even if the heater stays off. I hope it's not cracked that would be bad. I can weld so it's not terrible but it's also about decking the head after it's been welded that would either take a while or cost a lot.
I'm not too worried about the exhaust although they do suck. I wish they would just use stainless bolts and nuts. That would make life so much easier for everyone!
Do I need new head bolts you think?...

 

Yes, you need new head bolts.
They use "torque to yield" head bolts on most engines now.
These are torqued down to a specific ft/lb, .........THEN you turn the bolt 90 degrees as the final tightening, this stretches the bolt almost to the point of "yielding"(failing).
Once stretched like this, when loosened they don't return to original length and strength.
So you can reuse them, you just shouldn't.
What could happen?
Well best case would be a bolt would break when you were tightening it, that's the BEST case, worst case would be bolt "yields" when you are 100 miles away from home.

Most head cracks will be between valve seats in cylinder dome, that's a very weak point in almost all head castings, so while you could try to weld it, the work grinding and installing new seats(that will hold) might be in vain, kinda like the heads bolts in that regard, BEST case would be for you to decide the weld won't work and get a new head, worst case....break down 100 miles from home.

If you can ID the leaking cylinder with the glove test, it will make it much cheaper and easier, you will know where to look for fail gasket or a crack.


EDIT:
Was just looking at the 1999 Ranger 3.0l specs
They didn't use torque to yield head bolts, so you should be able to use them again, although it would be best to use new bolts.

Also if engine has not been overheat too much or too many times, and you can ID the cylinder that is leaking, you could just fix that one head gasket.
I have done this many times.
Get one head gasket, and bolts if you want
Since intake and exhaust gaskets are under 20ft/lb of torque I don't replace them, seal the water pass thru with silicone or other gasket sealer, and a light coat on the rest.
Exhaust gasket should be fine as is, it can be reused a few times.

I know some people will cringe at this but to each his own.
Heck when its not my money I always replace everything.
But the simple fact of the matter is when you start talking about the best way to fix something, until you say "buy a new vehicle" you are always wrong so it is a moot point in my opinion.
Buying a new vehicle is the top end of the "best way" to get a working vehicle, doing anything less is wrong, unarguably wrong, lol.

 

Thanks RonD.
OK so today is the day I will be doing the test and starting to fix the problem.
Is there anything else I need to replace while the motor is torn down? I was looking at the kits they have, I might just do both head gaskets while I have the chance. If the head is cracked, which I hope not, where can you get new heads and how much are they?
Thanks

 

I would first check with a couple of local Machine Shops, they often can get better deals on heads, so you end up paying the same locally than from buying on-line(with shipping costs), and then if there is a problem it can be dealt with locally.

Set of heads complete with valves should run under $350
Single head with valves under $200

Also since valves are not your issue a bare head(no valves), if available might be cheaper from machine shop even after they swap your valves to the new head, costs nothing to ask.

Getting a "used" head locally and taking it to machine shop for cleaning and testing might be the least expensive option, usually about $75 to have one head cleaned surfaced and pressure tested.

There were a couple of changes to the 3.0l heads over the years so make sure you get correct one for '98.
Also head bolts changed in '98, they got longer, since your engine could be a late '97 or early '98 you need to make sure on that as well.
When you get one head off look at the head bolt threads in the block, if all have recessed threads then you need the longer bolts, if threads are at the block surface then, '97, and shorter bolts

 

Have you checked the coolant level ?

If ok once the truck is heated up remove the radiator cap very slowly, it is hot and there will be blow back, see if there are any bubbles in the radiator.

Not saying Ron is wrong! no way! just do some checking before hand.