2nd gen 4.0 Overheating

Hi everyone. First time posting on this forum!

I have a 2005 4.0 Tacoma and so far absolutely love having it. However, there is an issue I have been having with losing coolant and the truck slightly overheating over the last 3 months. There are no visible coolant drips onto the ground/skip plate, it more seems like it boils out of the reservoir.

I have put in a new thermostat and I just replaced the water pump per mechanic's advice. I have also used an combustion gas tester to test for a head gasket leak and that test says there is not a combustion leak. It runs good for roughly two weeks, but then while driving it after a highway drive the trucks temp gauge starts to climb. In the past when this happens I just use a spill proof funnel to top off the coolant and burp the system. But, then in about 2 weeks or so the same overheating happens again. There is evidence of coolant getting sprayed up around the radiator cap/reservoir and even on the underside of the hood (see pictures).

Any one have any ideas of where/what the leak may be? Or is it possible I never truly get all of the air pockets out of the system and end up getting hot spots that cause the coolant to boil over?

Thank you guys for your time and advice in advance!

 

Sure sounds like a head gasket, especially after just replacing the water pump and thermostat. Possibly spraying out of the tank and blowing back while driving.

 

How long have you owned the truck?
How many miles on the truck?
Has the coolant been changed at recommended intervals (100K and then every 50K)?

I suspect that the radiator may be compromised.

 

@eherlihy, I bought it from private party last December. 140k miles and I have done a full coolant flush will the correct coolant type.
@six5crèéd would the combustion gas tester kit not pick that up?

 

I've never heard of a "combustion gas tester" until now, so I don't know.

 

@six5crèéd It is just a little bottle that goes where the radiator cap is. It has a blue fluid in it and with the car running it will change color if it detects exhaust gases. I don't know how good of a test it is, but reading online it seems like it should catch the problem.

 

Unfortunately it does sound pretty likely to be a head gasket issue and those early year models were subject to the head gasket problem. The testers that detect combustion gasses in the coolant are not 100% accurate

 

Pulling the spark plugs and scoping the bores will tell you if you have an internal leak - sure sounds like it is, unfortunately.

As a last ditch in case it isn't, pick up a UV dye kit and spike the coolant, then look for leaks next time you top it up. Dye is a lot easier to see than coolant especially if you have a leak in an odd place.

 

Man, looks like I may be replacing a head gasket. :/

 

The combustion gas tester isnt always accurate, there can still be a blown head gasket but just not enough gases in the cooling system to change the fluid color. You'll never get a a false positive with that test but false negatives are common.

Does it run rough on cold startup in the morning for a few seconds? And then smooth out? If yes that could be liquid coolant getting into the cylinders overnight when it sits

The slow loss of coolant with no external leaks is a big sign of a bad HG

Like mentioned above pulling the spark plugs, pressurizing the radiator and scoping the cylinders for coolant is the best way to confirm a HG leak. But you'll need some tools..

Maybe try a new radiator cap first since they're cheap? If the cap is defective it can let pressure out of the radiator too easily and it'll spray around the engine bay.. but similarly a leaking headgasket will allow combustion pressure into the cooling system and that will push coolant past the rad cap too.

Good luck

 

@b_r_o I do not notice it running rough in the morning. I will try scoping the cylinders to see the inside. I have already replaced the radiator cap with a new one so that shouldn't be an issue.
It could be a leak in the radiator but I doubt that given that I do not see anything visually.

 

A compression (leak down) test would be another way to check for a head gasket leak.

 

Try this first. We used it in my son's old Subaru (very prone to HG leaks) and it fixed the problem over the next 50k miles and 3 years before he sold it.
$ 15 is worth a try. Can't be more broken than broken so try to save yourself some real grief.

K-Seal® ULTIMATE - Best Head Gasket Leak Repair | K-Seal®

 

This stuff gunks up all of your coolant passages and will just lead to more headaches down the road. If it really is a head gasket you're better off just fixing it properly instead of jeopardizing your entire cooling system.

 

A HG leak won't show up on a compression test unless it's just completely blown out in which case you would already know it.

A leak down test might show it as bubbles in the radiator if it's bad enough but again isn't really a great test for a HG leak.

The best and most definitive test I've found is pressurizing the cooling system and looking into each cylinder with a borescope for coolant dripping in. Like the gas detection fluid it's not always a definitive test but if you see coolant in one or more cylinders you 100% have a leak.

Some HG leaks are easier to confirm than others, just depends on how bad the leak is, some leak more coolant into the cylinder than combustion gases into the cooling system and some leak more gases into the cooling system but coolant doesn't leak much back into the cylinder.