economycar

Hi, I want to start by saying that I have spent quite a bit of time searching this as well as other forums and I have learned a great deal. I have reached a point though where I felt the need to directly ask for help. I appreciate any help that can be offered. I recently purchased a 95 4runner SR5/auto. Soon after I found a situation where the coolant would boil over but not overheat. I was concerned and figured that the system wasn't sealed. After flushing the coolant and doing some maintenance, I still had a similar issue however it also began to overheat as well as have a hard time starting when hot. The truck has ~140k miles and I did a compression check which was surprisingly good with 195 psi on all six cylinders. It doesn't burn oil, no coolant in oil, it does leak oil, seemingly from the cam covers/seals and possibly oil cooler. The coolant gets a little dirty but not like a milkshake like by any means, it might be getting some contamination from somewhere. ATF looks ok on the dipstick but I didn't drop the pan or drain it, tranny functions with no problems.

This is what I have done thus far...
- flushed cooling system multiple times with distilled water
- used zerex "Asian Red" coolant
- new thermostat (gates)
- new upper and lower rad hoses (gates) with new constant tension clamps
- new OEM toyota radiator cap
- new OEM distributor cap/rotor, ngk wires, ngk plugs, oil change, atf top off, air filter, etc

Sometimes the truck runs fine, idles quietly at 750 rpm and other times it sounds/feels like a tractor (no offense to tractors). I feel like it correlates to the coolant situation but I could be imagining it. I did a pressure check of the coolant system and I corrected any visible leaks, the pressure does steadily drop but slowly and so I suspect that it is a very small leak. The boiling coolant/overheating is either the same problem as the hard start or separate, I'm not sure. The hard starting happens when the truck has been running and then sits, so if I drive it for an hour and then let it sit for half and hour and come back, it cranks but stumbles and doesn't want to start, almost feels like a fueling issue (like when carbs get heat soaked) however if I drive for an hour and shut it off and then immediately start it again, it usually starts so it seems like it takes a little while for the problem to develop. Right now I am thinking about bench pressure testing the radiator, my concern is that there is an internal leak with the tranny cooler portion but I really don't know. I want to know if this sounds like a situation that others have dealt with. I have also read many posts about the CSI, TPS and some other sensors, I do need to test those and I am resisting the desire to throw parts at the problem. Sorry for the very long post and thanks for any help.
Mike

millball

Test for combustion gasses in the coolant. Some auto parts stores will loan the testing kit.

It is likely that you have incipient head gasket failure.

scope103

I think millball is on the right track; while you describe "boiling over" it could be a lot of exhaust gases venting through the coolant.

A combustion gas tester just has a container with a chemical (bromothymol blue) that turns from blue (duh!) to yellow when mixed with CO2. CO2 shouldn't be in your coolant, unless being injected with combustion gases.

But you might have an extreme case anyway, in which a quicker/cheaper test is demonstrated in the first 90 seconds of this video:

economycar

Thanks for the replies. I actually did a block test today and it showed no problems, the fluid did not change color at all. Also, all cylinder seem to be firing, the plugs looked good after changing them and also after the last compression test which also came up with 195 across all cylinders. It's very strange. I ordered a new toyota thermostat and will probably get a new radiator (possibly from napa). I was thinking about doing a blue devil head gasket sealant just in case there is a small/intermittent leak that I am not picking up. Any other suggestions would be appreciated. Thanks.

millball

A clean block test is a good sign, but not absolute proof that a headgasket is sound.

A leakdown test is also in order, using the highest pressures that can be safely achieved. 200 PSI would not be to much, if it could be handled safely.

It's your truck and you can use any kind of sealants in it you want, but there's a special place in hell reserved for people who dope an engine with it and then sell it to an unsuspecting victim.without warning them.

Those sealants are near impossible to subsequently remove from any cooling system components.