Is this a bad head gasket?

[BoosTT]

On my 97 ranger 4.0L 4x4 auto, the temp gauge gets really hot then the normal in cycles... like overheating for 10 secconds then normal 10 secconds later. I'm pretty sure its the t-stat, but just want to double check. Does a bad head gasket change temps so quickly?

When I bought the car, I knew it was low on coolant this is why I am suspecting the bad head gasket. No other signs.

[Windsors 03 Cobra]

You got it, thermostat is fine.
Heat should go in and out like the temp gauges too, I thinks that air and coolant hitting the sender, the sender does not read steam or air.

[JaMichaels]

Is it smoking leaking? Sounds like a sticking therm stat. I've had that before on a 4.0 jeep.

[BoosTT]

Not really any smoke. I don't see any leaks either. I think it's a very very small head gasket issue. I did the ghetto fix of stop leak and I haven't lost any coolant yet (about 100 miles).

[Al]

Check the coolant level.

[BR3W CITY]

does it change when accerlating or revving? I have had a water pump with a damaged impeller, and when sitting or at low rev's it would heat up, but on the road it would maintain normal temp.

Air in the system is my second guess.

[BoosTT]

RPM, speed, idle time do not make a difference. It's random. I ordered the t-stat. It was only $15... worth a try.

I've been watching for air in the lines... nothing so far though. Is there a technique to blead the system?

[sloLs1]

rangers have knowen headgasket problems on the driver side front of the head... it starts out as a very small leak and it usually doesnt drip.... check to see if theres any "dryed" up coolant there. but it does kinda sound like a thermostat issue or low coolant issue.

[Coops Brother]

I've replaced many T-stats in 4.0L fords for the same erratic temp readings....

[84hurst]

My old '93 with the 4.0 did the same thing. Once it got up to temp (middle of the guage) it would cool down by about half and just kinda bounce around in that range. Never had a problem with the heat either.

[theavenger333]

other easy way to check is check the oil. even if its a little bit of coolant it'll still separate from the oil. could also be a bad temp sensor?

[lordairgtar]

Maybe you have an air pocket? Do you get heat all the time or are there times during your drive when the heat seems cold?

[FoxStang]

Does the top of the inside of the oil cap have any white, foamy residue?

[BoosTT]

I just changed the oil and the old oil was fine. Heat does blow cold some times.

[sloLs1]

other easy way to check is check the oil. even if its a little bit of coolant it'll still separate from the oil. could also be a bad temp sensor?

not always does a headgasket leak into the oil... on these particular motors they usually leak externally....


still sounds like you have an air pocket in the system... is it using any coolant??

[BoosTT]

Coolant level hasn't changed since I had it (100 miles). I'll replace the t-stat as soon as it arrives. That'll give me another place to look for an air pocket too.

Thanks for the help guys! I'll let you know how it goes.

[sloLs1]

Coolant level hasn't changed since I had it (100 miles). I'll replace the t-stat as soon as it arrives. That'll give me another place to look for an air pocket too.

Thanks for the help guys! I'll let you know how it goes.

ooo i must have misread... i thought you already replaced the t stat. thats prolly your only problem.

goodluck

[BoosTT]

I'm pretty sure it was the t-stat. I need to put on more miles to verify though. Thanks!!!!!!!!!!!!!!!!!!!!!