Head Gasket? Water Pump?
 

So this week I noticed a slight rattle in the front of my 1990 eliminator. Upon investigation I found the idler pulley bearing was shot. During my snooping around I noticed some bubbling in my coolant overflow tank at idle and a little had been leaking from the cap. I revved the engine a bit and the bubbling gets worse. I have been noticing temp running about 160 continuously, but that may be attributed to the 5-25 degree weather we have been having as well. I have the belt off and the water pump pulley has no play in it. I started the engine with the belt off and did not notice the bubbles in the overflow tank, and didn't notice any when revving either. Did not run the engine for long since the belt is off and didn't wanna get too hot. Any ideas? I was thinking it was head gasket at first, but the lack of bubbles when running without the belt has me second guessing that idea.

This is on a 1990 Comanche Eliminator with a 4.0L all stock.

Thanks in advance!
Mike

First off 160° seems too cold, granted it's cold outside, my 4.0 runs 200 - 210 whether it's 0° or 90° outside. Has it always run this cool? Does it take a long time to warm up? Sounds like maybe it could use a thermostat, maybe the one that is in it failed open and is not allowing the engine to warm up completely. As for the bubbling that only time I recall seeing bubbles in the overflow is if the engine overheated or I recently did work on the cooling system and it's working out the air. If you're concerned about a head or head gasket and think you may be getting exhaust into the coolant there are test kits that test for the presence of exhaust in the coolant that will tell you if you have a problem. I'm not surprised you didn't see anything with the belt off and engine running since there is no coolant circulation. Some others on here may have some more insight.

You need a 195* thermostat. Sounds like you don't even have one, or it's stuck open.

Also, if you've got the original expansion bottle, put a 703-1396 cap on it from Napa.

Thanks guys, I'm gonna go pick up a stat and the cap. Ill install the idler pulley and belt and run it again afterward. Will update when I can.

I just recently got the truck and worked through a fuel problem that was related to the pressure regulator and it has been running 160 since I got it. but I've only driven it longer than 20 minutes 3 times since the fuel issue has been resolved.

Excellent plan.

So quick update. Stopped in at NAPA before work and picked up the 195 degree stat, and had them order in the Volvo expansion tank cap(will get that in the morning). I removed the old stat, it was a functioning 180F stat. Installed my idler pulley and belt, topped off the coolant and started the truck. I idled for around 5-7 minutes and allowed the system to work the air to the top then installed the stock cap. Temperature climbed to right at the 210 degree mark. I noticed the upper hose has a constant flow into the expansion tank, I do not know this cooling system so I'm unsure if this is normal. Drove the truck for about 10 minutes and brought it back to the garage, did not have any leakage around the cap after this.

The truck smoked white on startup for a few minutes with average condensation coming from the exhaust pipe. I smelled the exhaust and didn't notice anything out of the ordinary.

The rattling that I assumed was only related to the idler pulley is also still there. It was not there when starting the engine without the belt however.

Hopefully the white smoke is just normal water vapor and not coolant, sounds like you know what you're looking for there but I would just keep an eye on it. As far as the rattling noise. A trick I learned for tracking down that type of thing is while the engine is running take something like a long screwdriver and place it on the different components you think might be making the noise and place the other end to your ear. You will hear the noise conducted through the screwdriver. This helped me track down a noise that I thought was in the valves, turned out to be the distributor. Obviously be very careful while doing this so you don't damage anything or yourself.

Check the harmonic balancer and all other pulleys.

Received the cap for the tank today, found the balancer is also starting to fail so I ordered that and the block tester kit from NAPA this morning, they will be in tomorrow morning. I figure the block tester will answer my questions about the head gasket since I am up in the air on it still. I will reply again once the test has been done on the cooling system. As for the balancer if I test positive for exhaust in the cooling system ill wait until I have the head tore off before I install it, incase I were to for some reason find catastrophic damage. Which I doubt I will but would potentially save a few bucks if that were the case. Thanks again for the tips and help Cruiser and GreenMan!

Balancer was roasted, as well as alternator shaft. I have replaced both components. I also used the napa block tester to check the cooling system for exhaust gases and it came back negative. Truck is running like a top with the new balancer and alternator. Will have to keep an eye on the expansion tank cap for leakage. The new cap appears to be doing the trick

Don't ya love simple?

definitely! and cheap!

Simple AND cheap can't be beat.