Carnut68

For the past six months my 1994 22RE 5 speed pickup (170k miles but engine was rebuilt about 20k ago by prior owner) has had a surging idle and coolant issue that I can't figure out. I have owned the truck for almost five years and it ran fine previously. I replaced the idle air control valve under the throttle body before I realized the surging idle is really caused by the low coolant issue. I will describe the symptoms as best I can. After the truck is running for a few minutes but before the thermostat opens the idle starts climbing and the coolant level will start rising. If the cap is on will get pushed out the overflow but I am using a coolant funnel in the open radiator neck. Eventually this triggers the notorious surging idle. I know burping these engines can be an issue so I am doing this on ramps with the cap off. If I squeeze the upper radiator hose a bunch of times eventually air bubbles come up and/or the thermostat will finally open and the coolant will all drain back into the radiator. Then the surging idles stops and the RPM goes back to normal range of 900 from about 2000. However after another few minutes the whole cycle starts over again. I feel like I have done everything I could to burp this so I think an air pocket seems unlikely. I know people will question the head gasket but I have used a block tester and it doesn't show any combustion gases in the coolant. Nor is there any white smoke or sign of coolant in the oil or the other way around. Any coolant losses seem to be out the overflow. Could it be a blockage somewhere or a stuck thermostat? I replaced the thermostat about a year or so ago and I didn't have these issues after the replacement. In full disclosure, I also have an EGR fault..which I have had for a long time...and the exhaust has some holes some of which may be around the 02 sensor. I am replacing that whole system. I don't believe the EGR or exhaust is related but I thought I would mention them. This truck is in really nice condition body and frame wise, I just need to sort out the mechanicals. Appreciate any guidance.

Co_94_PU

iTrader: (-1)

With the vehicle level the high spot is located at the heater control valve in the firewall. You can disconnect the engine hose at the valve and it will purge the system of air when you fill the radiator.

It's worth checking your radiator and the cap. Caps fail and doesn't hold pressure, there is a tester for this. Also if it's a new style plastic radiator any molding ridges on the sealing surface can impead the seal..

900rpm seems a little high.

Carnut68

Thanks but since I have the front wheels on ramps, I thought the high point is now the radiator neck and any air trapped in the heater core should work it's way out. Is that not, correct? Also, I think the radiator cap is newer, but regardless with the cap off I don't think it should push coolant out the radiator neck. 900rpm may not be the correct idle but until I get the coolant and associated rising and surging idle issues resolved, I don't know where to set the idle screw.

millball

I have seen radiators that have a 'DAM' built into the upper hose outlet that make it appear that the radiator is full to the top when the truth is far from that.

I found that a 'standpipe' installed at the radiator cap was necessary to get the system filled.

Co_94_PU

iTrader: (-1)

Assuming lots here..

Radiator cap is properly sealing with the radiator.
You're using something like the "lisel bucket funnel", and the bubbles eventually stop when attempting to burp the system.
You never moved the idle screw or altered the throttle linkage.

..
There are uh three(?) Ways air can enter the system.

Your over flow tank lines aren't sealing properly so instead of coolant it sucks in air when the system heat cycles to cold. (Put new lines and or clamps on them)

Inspect the coolant lines, you want to look for protruding and or wet cords which indicate a failure of the hose. (You should replace any hoses with wet cords exposed on the cut ends, as they have failed internally. Or any hoses that buldge. These both can also suck air into the system on heat cycles.)

There is also a case where the water pump seal starts to suck air in via the weep hole, you might notice some weaping from the pumps weep hole which is located at the lower side of the shaft area.

And finally your HC test of the cooling system lied to you for what ever reason. (For example during combustion the breach seals itself due to the super high pressure but is not sealed during the compression stroke.. It pushes in some air and a bit a fuel into the coolant passage, then the ignition fires and the high-pressure wave seals the failing gasket)

snippits

Low coolant will definitely cause surging idle. A bad idle air control valve caused a random surging idle on my 92 22RE.

Coolant is going out the tail pipe as steam, or you are not getting the system purged all the way. If the thermostat was stuck closed, it would run hot. If it's stuck open, the heater output would be low.


Pull the hoses off the idle air control from both ends, and check to see if they are clogged up causing the idle air valve control to not get the right amount of coolant flow.

Sonman33

Did you ever figure out the problem? I have the same issue going on. I have just had an engine rebuild and have replaced almost everything you can. My coolant keeps going out the overflow and i can hear it bubbling. Replaced thermostat and that helped the surging idle but after 40 miles the coolant overflow is back. The thermostat stays in the middle and does not overheat. Any help is appreciated.

Carnut68

Yes, it turned out to be the head gasket unfortunately. Been running great ever since that was replaced.