replaced headgaskets.now slight idle surge and running cool with temp fluctuation

[91rangerdanger]

So I just replaced the heads and head gaskets on my 91 4.0 ranger. Started fine properly bled the cooling system now the idle surges slightly a few hundred rpm at most and temp gauge doesn't go past the o on the normal on the temp gauge. It got up to m once and went back down. Normally rests on n with a slight fluctuation up to r then back to n I put a new thermostat in as well. No air in the cooling system heat it great upper and lower rad hoses are hot along with heater core hoses.

Any ideas?

 

[doorgunner]

So......you DID turn on the heater for about 10 minutes.....air can be hard to get out of the system sometimes.......

New coolant will affect things/gauges....

NO coolant/just water will affect things also.....

New heads flow better causing lower gauge temperature readings...

keep a close watch on temp gauge while you "break-in" the heads....

 

[91rangerdanger]

Yes. Before I started the truck I made sure the rad was full of.coolant started the truck and.turned on the heater. Ran for more then ten minutes before driving. Rad cap was off with my rad full kit.on basically a rad cap with a funnel attached to it. I watch all the air come out. Waited till there was no bubbles at all for at least five minutes.

What do you mean breaking the heads in? I've always just slapped em on and went. Unlike a fresh bottom end there isn't really any moving parts that need to be mated together.

Truck runs fine other then the slight idle surge and running cooler then IM used too

 

[Andy D]

Maybe something is loose, There is always something that needs a little more fixing after such jobs. Vacuum leak? The temp gauge on the Rat doesnt inspire confidence, It could be a painted needle. I would try for a more accurate temp reading before I started throwing parts at it. Is the engine running rich? The neat thing about cool runnings is that th only thing you need worry about is gassing the oil. My personal preference is a 195' thermostat as a baseline. The Rat idles at 1200 rpm until it warms up. After 10 minutes it settles down to a 700 rpm idle. My BMWs idle at 600 with a turn of a key, so I'm spoiled. But, it is a problem that isn't worth fixing. It reminds me of my old carbatated Grand Wags.

 

[91rangerdanger]

All vacuum lines seem to be hooked up properly except one. Can't figure out where it goes so it's plugged. From a cold start truck Idles about 1200 then drops to between 600 and 700 with a slight idle surge. Truck doesn't seem to be running rich. I'm getting about 16-17 mpgs Turning 33x12.50 mud terrains.

 

[doorgunner]

What do you mean breaking the heads in?

Sorry.....I was thinking about Harley Davidson heads (aircooled & require a couple days of short trips to seat everything)

 

[Kadams87]

I just did heads on my 4.0. As for the coolant, My truck runs right on the O and the heater works and all. I think you are fine there. The surging Idle though, I replaced my IAC and that solved my issue, I could have probably cleaned it up and it would have worked fine. What are your plugs gapped at and did you replace them. I put good ol Motorcrafts in mine.

 

[wildbill23c]

My grandfather's 93 Ford Ranger 4.0L's temp gauge was always all over the place, I think the gauges are just junk to begin with, they're really only an idiot light they don't really measure the temperature in any sort of accurate mannor that would mean anything by looking at the gauge. The gauge cluster in my 84 B2 doesn't work, so I installed the 3 gauge kit from Autozone and I find it pretty accurate, which is something I would personally look into rather than the dash gauge. The aftermarket temp gauge actually gives you a pretty accurate temperature readout. I know my 84 B2 will work its way up to about 200-210 degrees if I am pushing it hard, but it will drop right back down to around 190 degrees pretty quickly.

 

[Kadams87]

I just did heads on my 4.0. As for the coolant, My truck runs right on the O and the heater works and all. I think you are fine there. The surging Idle though, I replaced my IAC and that solved my issue, I could have probably cleaned it up and it would have worked fine. What are your plugs gapped at and did you replace them. I put good ol Motorcrafts in mine.

I forgot to mention, Mine would surge up to the M once or twice every morning on my way to work and then level out on the O, I couldn't get it to stop, I bled it and did everything I could think of. But after a long drive to Austin in 80 degree weather with the A/C on and Fway speeds it hasn't done it since. Only thing I can think of was a mystery air pocket that only showed it's face when it was cold.

Also did you get the grounds back on correctly after you did the heads? I remember helping someone out with wild gauges after they did a motor in their Ex and it ended up being bad grounds.

 

[RonD]

Surging idle can also be loose intake bolt, re-torque upper and lower


My '94 4.0l had a partially blocked heater core, still blew hot, but it caused temp to vary, never hot just above the "O" and then back, and very random, no engine load or outside temp relationship.

Replaced a few parts but it didn't change, read a thread here about the heater core, changed it and all is well, gauge doesn't do the dance any more.

 

[91rangerdanger]

Wow guys thanks for the replies. My temp guage has since leveled itself out and sits steady on the O. very rarely will it go up any higher. Was even out pushing her hard in the mud today and ran like a champ. Idle surge seems to come and go. Sometimes it idles nice and smooth and other time it surges a bit. I think im gonna pull the IAC and either replace or clean it.

 

[Kadams87]

Wow guys thanks for the replies. My temp guage has since leveled itself out and sits steady on the O. very rarely will it go up any higher. Was even out pushing her hard in the mud today and ran like a champ. Idle surge seems to come and go. Sometimes it idles nice and smooth and other time it surges a bit. I think im gonna pull the IAC and either replace or clean it.

Sounds you had the same mystery air pocket I had. Hopefully the IAC fixes it, if not then the TPS could be at fault also. Is the surge temp related?

 

[91rangerdanger]

The surge does not seem to be temp related. It's random. When I first got the truck running after I replaced everything it was more frequent. Now it's not as frequent

 

[Kadams87]

The surge does not seem to be temp related. It's random. When I first got the truck running after I replaced everything it was more frequent. Now it's not as frequent

Taken a can of MAF cleaner to the ol MAF Sensor lately?

 

[91rangerdanger]

No i havent lol. That actually may not be a horrible idea seeing as how i havent cleaned the MAF yet. and since ive had the truck ive been through some hellish mudholes and had an airfilter that was 99% blocked/worthless