Toyota troubles

[ftpiercecracker1]

So my brother's pickup blew the top radiator hose to smithereens a few days ago. Immediately after replacing the hose the truck started to overheat and run rough, significantly more so as the truck gets hotter.

 

The truck has over 250k on the clock, but has been 100% issue free since bought (70k miles ago)

 

It is a 98 2.7L 4cyl manual toyota pickup, don't think they had started calling them tacomas yet.

 

 

Done thus far:

 

Replaced the t-stat with a verified good one (boiling pot of water and a thermometer trick)

 

Flushed and rebled system several times. Original coolant was very rusty.

 

Compression test, front 120, 120, 150, 150, back.

 

Spark plugs have good color. Aren't blackened/gas soaked nor do they have white ash from burning coolant. No smoke out tail pipe either, minimal water.

 

Pulled WP to check fins, perfectly intact.

 

 

I suspected the radiator because when it's hot, the top is to hat to touch while the bottom remains ice cold even as it boils over into the overflow tank. HOWEVER, after removing said radiator I used a garden hose to check it's flow and it appears to have no restrictions. Water flows out the bottom as fast as I pump it in.

 

I have a new rad coming in tomorrow, going to see if it makes a difference, other than that I am at a loss as to why it continues to overheat.

 

Thoughts?

[Minuit]

Oops. Didn't read.

 

(although making sure the cooling system is free of air might be worth trying anyway)

 

Was it overheating when the upper hose blew? If not that strongly suggests something happened in the process of replacing the hose, although radiator hoses usually don't just explode for no reason.

[1987Comanche]

Are you sure the head gasket is ok?  The low compression readings on 2 adjacent cylinders make me wonder.  You can pick up a cooling system pressure tester at O'reilly's (loaner tool) and see if the system holds pressure. Might be worth getting a few test strips to check the coolant for exhaust gas as well.

[ftpiercecracker1]

Are you sure the head gasket is ok? The low compression readings on 2 adjacent cylinders make me wonder. You can pick up a cooling system pressure tester at O'reilly's (loaner tool) and see if the system holds pressure. Might be worth getting a few test strips to check the coolant for exhaust gas as well.

 

Good advice sir.

 

Well I thought the high numbers ment the HG was fine but that is apparently not the case.

 

Using the shop air I pressurized the cyliders (TDC, of course). Cylinder #1 immediately started bubbling water/air out of the radiator.

 

Cylinder #2 was pushing air out the tailpipe ever so slightly.

 

I haven't even bothered with 3&4 because it seems blatantly obvious now that the HG is indeed blown.

[1987Comanche]

Glad I was able to point you in the right direction :thumbsup:

[ftpiercecracker1]

Now the only trouble is if the head needs to be decked. We found a low spot and it correlates to where the HG blew. The depression is about the size of quarter, maybe a little smaller and is about 5k of an inch at its deepest. The rest of the head surface seems uniformly flat.

 

We used a straight edge and a dollar bill to check.

[1987Comanche]

0.005" is asking a lot of the HG.  I'd drop it off at the machine shop for a pressure test and a skim cut to clean it up.  Have them pull vacuum on the valves too to make sure they're sealing.  I'm not a big Toyota guy but, in general 0.002-0.0025" is about as much warpage as you can handle with an AL cyl head.

[ftpiercecracker1]

Thanks a lot for all the info 1987comanche. I will definitely pass along the advice to my brother, he felt it needed to be decked as well.