My 97 4.0 v8 with 175k automatic when in park or neutral will idle very high, anywhere from 1600-2000 rpms. it seems like it’s partially the vehicle warming itself up because it starts higher and lowers itself after getting up to temp. But then randomly at Times the rpms will spike upwards of 2000 rpms and my temps will reach 230 ish. then the rpms will settle back to 1600 ish and the temp will drop back down. The temp will do exactly the same if I’m in gear but he rpms will not spike in correlation. Each time it happens it seems to quickly lower itself to around 185.

so far I have changed the following.
thermostat to 185
water pump
fan clutch to HD
Drained and refilled coolant multiple times
made sure all coolant lines are serviceable

I have tried looking for a vacuum leak using carb cleaner while the engine is running and spraying it to find a leak but I haven’t found anything that intakes at all. The odd thing to me is that when the rpms spike up the throttle body doesn’t move at all. So my TPS isn’t faulty or it would be opening the valve. Maybe I just need to bleed it better, but I’ve tried everything to bleed it as much as possible.

my ideas: due for a new battery but I doubt that would cause this
very very tiny leak between water pump housing and engine. Less than a drop a day but maybe it could effect it.

hopefully someone can give me some advice! Thanks guys

 

Temp spikes up to 230 makes me think there may be pockets of steam in the cooling system.

What oil are you running? Last oil change?

 

Right now I’m running valvoline full synthetic high mileage 10w-30, las oil change was probably 2k miles ago

 

Have you looked into RobertF's app/program to reset your adaptive values?

 

I haven’t. Honestly all the computer app stuff is a little beyond my knowledge. I just drove it around again and I could still hear some bubbling behind the dash, I think my miniscule leak at the water pump housing may be pulling some air in. I’m going to try and seal it up with some heat resistant RTV. I’m also putting in a new battery and I’m going to change the engine oil just to cover my bases. I have an engine temp sensor on the way as well so hopefully all of these things will solve my problem. I’d like to learn more about the adaptive value resets as well though

 

Hang in there, this forum has excellent people who can help keep your truck on the road.

If you hear bubbling you have air in the cooling system and it needs to come out. I used some gasket making RTV to help prevent any leaks around the thermostat. Get the front passenger side up as high as possible for another coolant bleed.

 

When you bleed which caps do you leave off/on? When I’ve been doing it I leave the reservoir cap on and put a funnel in the radiator plug and try to get all the air out of the hoses

 

As for the bleeding your almost there. Here is how I do it.
Get the front end up high if you can.

1. Leave both caps off.
2. Keep coolant to the proper reservoir level.
3. Start the truck with heater on Max, but have the blower at #1 position.
4. Look for air bubbles coming to the surface of the radiator as the thermostat will eventually open.
Put a bucket/pan under car to catch any coolant.
5. Keep coolant to the proper reservoir level.
6. When you feel heat coming from the inside heater vents that is a good thing.
7. Close up the radiator, and put the cap on the reservoir.

A couple of hours later return to car and fill reservoir to proper level.
Remember to be patient with step#4 as the truck will need to heat up to get the thermostat to open.

 

Thanks for the help man, it seemed to have worked pretty well. Hopefully all that random spiking didn’t fry or break something in the engine, can’t tell if I’m hearing noises or just paranoid lol.

 

Your welcome.
This forum is all about learning and sharing so we can keep our trucks safely on the road with confidence.
Are you using an UltraGauge to measure your engine specs?